UK damp &
decay control

This is an edited version of an articled entitled-Wall base damp: Is one horizontal damp-proof course sufficient dampness protection? written by Ralph Burkinshaw

Over the past 40 or more years, it has been common practice for some in the property industry to label nearly every patch of damp just above a ground floor skirting board as ‘rising damp’. That ‘diagnosis’ has been made usually from visual evidence and moisture meter checks alone.

Standard treatment of ‘rising damp’ has usually been the insertion of a chemical-injected damp-proof course (DPC) together with the application of protective solid plasters as a final defence to mask the dampness. This might well be termed ‘damming the damp’. This kind of remedy may not target the root cause of the dampness, but merely mask the symptoms and eventually the dampness may resurface. Money spent on chemical injection DPCs and the associated protective replastering in many cases might be more usefully spent on a remedy more targeted to the root cause.It could also be argued, however, that there are some occasions when such damming of the damp might be the only realistic alternative—for example, when a dry wall surface suitable for decoration is needed quickly. There is sometimes not the time or the resources to follow through a more thorough building examination and long-term cure. .

During the 1990s a number of surveyors and researchers strongly challenged quick-fix solutions to dampness problems, with one or two even claiming rising damp to be a myth. But the debate was to a certain extent groundless, as, to my knowledge, there was never a workable definition of ‘rising damp’ until the following was published (Burkinshaw and Parrett, 2004):‘Where moisture travels upwards through the pore structure, or via small fissures or cracks, or as water vapour, against the forces of gravity, typically up a wall or through a floor from a source below the ground.’ .

Certainly, many low-level dampness problems have resulted from low-level dampness penetration or plumbing leaks. In such cases, dampness does indeed rise or soak upwards, but usually from around ground level. For the purpose of this paper, any dampness found at a low level in house walls is termed ‘wall base damp’.Whether or not such problems should be described as ‘rising damp’ is not really the most important issue. When dampness is found, and it is causing a problem for the building or users of the building, more than anything else the cause needs to be found together with a solution to put the problem right. It is less of an issue whether the damp should be labelled ‘rising damp’, ‘penetrating damp’ or any other ‘damp’, and there should be no automatic remedy for any cause of dampness. .

Most houses built since 1877 actually possess a horizontal DPC and, if this is intact, dampness from below the ground only would be a real threat on a very wet site. Unsuitable changes in and around the building, however— such as the raising of external ground levels — increase the risk of low level damp penetration, but it is the height of external ground in relation to vulnerable floor timbers or easily reachable plasters and decorations that is the key factor. Whatever the height of the horizontal physical DPC it would not prevent lateral damp penetration. Timber will now be less high up in relation to external ground level, floor ventilation will be compromised,routes for damp penetration through the wall base will be created via air vents and poorly maintained masonry and the floor oversite level or ‘solum’ now will be lower compared to the external ground level, making it more likely to become a water collection zone. Water splashing and pooling from rain is free water in significant quantities and free water can soak and trickle into porous low-level masonry at will. In a traditional masonry house, dampness may be prevented from causing problems by subtle combinations of wall base detailing. The first line of defence may be the dual protection of a horizontal damp proof course and a vertical wall base plinth. This in effect creates protective ‘L’shaped damp protection. In addition to these two ‘barriers’, moisture may evaporate out on both sides of the wall base, i.e. within the floor void and externally. Wall base finishes and the amount of sub-floor ventilation will influence the amount of that evaporation. The way in which the wall base takes in and gives out moisture needs to be carefully balanced to keep damp at acceptable levels. .

Rainwater splashing and collecting at the intersection of a wall and the ground should not be allowed to soak too readily into the wall base around ground level, and an effective plinth (or perhaps dense low level masonry), coupled with good surface water drainage, is the key. .

The intersection of a wall base and the ground creates a ‘ledge effect’ where lateral water penetration can be a problem. This effect can be seen at all heights of a building, e.g. just above a decorative cornice, near the top of an abutting boundary wall, or even where builders’ rubble is piled up against a wall. The way moisture may be managed by drainage, evaporation or barriers was well described and illustrated by Peter Bannister at the Aston University Conference on 3 November, 2004:‘Dampness and Decay in Buildings – The Whole Solution’. .

The Building Research Establishment (BRE) has over the years largely ignored low-level lateral dampness penetration, choosing to emphasise the threat of dampness from the ground or dampness penetration into the building at a higher level, for example, on exposed south-west elevations or via poor detailing of openings, or poorly installed cavity fill insulation.Low-level dampness penetration at the wall base is usually only referred to in the context of frost damage, where less durable bricks could become wet below a DPC and be damaged by the expansion forces from freezing. In the author’s view, the BRE usually over-emphasises and misconstrues ‘bridging’. It is always assumed that a huge store of water is ready and available — waiting in ambush from a below-ground source — to track, i.e. ‘bridge’, around a DPC via porous renders and plinths to cause damp havoc above it. It may be more likely that this moisture was mainly soaking into and collecting in masonry near ground level from the vast volume of water splashing, pooling and soaking into the wall base every time it rains. Again, in this case, the position of the horizontal DPC may be less of an issue. .

SUMMARY POINTS.

A physical horizontal wall DPC on its own may not provide adequate dampness protection to the wall base and adjacent timber floor members. .

A horizontal wall DPC controls movement of moisture from above and below. .

Installing multiple horizontal DPCs may still not prevent low-level lateral damp penetration. .

A horizontal wall DPC controls upward movement of moisture that has penetrated the wall base between the ground and the DPC, as well as controlling or sometimes stopping moisture originating from below ground. It should not be forgotten that much of this localised belowground moisture can result from inadequate rainwater disposal arrangements around the building. Just consider the amount of rainfall per square metre over the whole site compared to the sheer concentration of rainfall load at the bottom of each downpipe. .

In traditional houses built with solid walls, a vertical DPC may be needed below the horizontal DPC. Traditionally, this has been by way of a cementitious plinth or sometimes vertical slatework or asphalt. .

Even simple damp problems can be a mystery and a challenge at the early stages of investigation on site until all the pieces of the jigsaw finally piece together. Once diagnosed, all the symptoms presented can seem as clear as day. .

Pro-active surveying is the order of the day. Always lift floorboards, take measurements, pour water, make observations and analyse findings. .

A methodical manner should be adopted on site. Explain what is planned and how it might help to drive the investigation. Most occupiers will allow the surveying to be taken further than previously thought possible. Stained wallpapers and salt-laden plaster is already defective and became defective months or years before a surveyor arrived on site to scrape or drill it. .

Dampness investigation is not just checking with a moisture meter just above the skirtings near the end of a building survey, it is integral to the survey from chimney pot down to foundations. Dampness is always cited as the commonest cause of building defects. .

Diagnosing damp is time-consuming and sometimes invasive. But spending hundreds of pounds on further investigation of dampness may save thousands. Many homeowners, facing a ‘nightmare damp’ scenario from flood, mould, rot, or salt-damaged plaster, now wish they had invested in a fuller investigation of dampness prior to purchase. .

Drawing a sectional sketch enables one to understand the construction technology of the wallbase, which will help diagnose the cause of the dampness and formulate a remedy. It is useful to compare the detailing as found with current building regulations or with examples of more traditional construction that has proved satisfactory over the years. .

Few chartered surveyors possess the resources in terms of time, equipment or expertise to carry out intensive laboratory-style investigation such as ‘the sampling method’ offered in BRE Digest of1986 on rising damp, so practical site investigation methods are needed. .

For more information about the accurate diagnosis and effective treatment of rising dampness from the ground please contact UK DAMP & DECAY CONTROL on 0800 028 1903 or email enquiries@ukdamp.co.uk

INTRODUCTION

There is a lot of discussion in the media and on the internet about rising damp – what it is, misdiagnosis and whether it even exists.
Rising damp is simply water from the ground that enters a structure by capillary action – the tendency of water to be drawn upwards in porous materials. Building materials are porous, therefore moisture from the ground can rise into the structure of a building – much as water is drawn into a piece of tissue paper or a sponge – unless there is a barrier, such as a damp proof course, to prevent it from doing so.
The problem causes discoloured wall coverings, often with a characteristic tide-mark due to salts dissolved in the ground moisture evaporating out towards the top of the profile.
Due to the fact that there are many other causes of dampness in buildings, such as rainwater ingress and condensation – as well as the high cost of remedial work for rising damp – it is vital that investigations into a suspected case are undertaken by a trained and competent surveyor, such as one who holds the CSRT (Certificated Surveyor in Remedial Treatment) qualification.

CHARACTERISTICS OF RISING DAMP
Rising damp is characterised by a descending moisture gradient within a wall from floor level up to a height of about 1.5 metres, although on rare occasions an impermeable covering on the face of a wall at lower levels, may cause the damp to rise higher than this.
A good indicator that a damp problem is being caused by rising damp is the presence of a salt deposition line. Ground salts migrate in solution with the moisture and will be deposited at the point where the water evaporates from the wall.
Sulphate salts will produce efflorescence on a plaster surface, whereas chloride and nitrate salts are hygroscopic, that is they attract moisture from the atmosphere and are seldom visible, although they can cause a line of increased dampness on the wall. While harmless to health, such salts can be responsible for damage to plasterwork and other wall coverings. Salts will continue to evaporate out long after a rising damp problem has been resolved unless the wall is resurfaced with salt resistant plaster or render.

RISING DAMP DIAGNOSIS TECHNIQUES
There are three phases to any investigation and diagnosis of damp in a building:
1. Visual inspection
2. On site measurement of the extent and severity of the problem
3. Laboratory analysis of samples

Visual Inspection
The first task when investigating a suspected case of rising damp is to carefully examine the property in order to fully understand the building, as well as the client’s requirements and expectations.
When determining the presence of any moisture in the fabric of a building it must be understood that no method of diagnosis can differentiate between water from one source or another, so all potential causes of dampness – including rainwater ingress and condensation – must be taken into consideration.
A visual inspection will therefore involve a thorough check of the common causes of dampness, such as faulty guttering, downpipes and flashing, as well as damaged pointing, cracked rendering and raised external ground levels. Rising damp can be caused by excess water pooling around foundations, such as might be caused by leaking water pipes.
If faults are found by a surveyor, the client should be advised to remedy them, allowing a period of time to elapse before further checks are made.
Only when all construction defects have been identified or eliminated from the investigation, should the effectiveness of the building’s damp proof course be assessed.

On Site Measurement
To support the findings of a visual inspection the surveyor will then begin the process of quantifying and developing a full understanding of the damp problem. There are two types of moisture meter commonly used by surveyors during site investigations.

Electric moisture meters are commonly available and used for on site testing and screening. The vast majority measure either the electrical resistance of the wall materials, or the capacitance in a sensor, both of which are influenced by moisture.

These meters are quick and easy to use, have the advantage of being small and portable, and are valuable tools if used properly. Being non-destructive they are particularly suitable for pre-purchase property surveys. However, there are limitations to their use which must be understood by the operator. Readings from electric moisture meters can be influenced by many factors, such as salt contamination, material density and the conductivity of different wall coverings. Reasonably accurate measurement can only be achieved on timber. If used on plaster or masonry, readings can be inconsistent and are not truly quantitative and readings from different situations should not be compared.

For this reason isolated readings from electric meters are generally of little value. However, electric meters can be used to take a number of readings very quickly, so they are particularly useful in establishing a pattern of relative readings over a surface.

Electrical meters are not suitable for checking the efficacy of a new damp proof course in a building that has previously been suffering from rising damp, as the presence of remaining salts can produce high readings.

A calcium carbide meter, often known as a ‘Speedy’ meter, can be used either on site, or as part of a laboratory-based analysis. Samples are obtained by drilling a hole in a wall and collecting some of the dust, a measured sample of which is placed within a pressurised container and mixed with calcium carbide. The calcium carbide reacts with any water present, producing acetylene gas, the volume produced determining the moisture content of the sample.

The calcium carbide meter is a very useful tool for assessing the exact moisture content of a sample, but training is necessary to in order to correctly interpret the results. The meter can only indicate the total volume of water in the sample tested and cannot differentiate between capillary and hygroscopic water.

Laboratory Analysis
In order to achieve precise quantitative results a laboratory analysis is vital. A variety of tests are available, giving more comprehensive results than on site testing. Analysis in a laboratory is also necessary to accurately determine the presence and concentration of ground salts.

Gravimetric, or oven-drying analysis is able to distinguish between moisture derived from the ground and that due to existence of hygroscopic salts. It involves removal of a drilled sample from the wall which is weighed and then left in a controlled environment – at 20 degrees centigrade with a relative humidity of 75 percent – to be allowed to reach its equilibrium weight before being weighed again. The sample is then oven-dried and reweighed. The difference in weights can be used to accurately determine the hygroscopic and capillary moisture content of the sample.

Although this test takes some time and will be more costly to undertake than on-site testing, it is the most accurate test currently available.

Moisture Profiling
Moisture profiling can be particularly useful when diagnosing rising damp. This involves taking a series of vertical samples in order to establish the distribution profile of salt and moisture within a structure. Although relatively expensive to carry out, the process can be useful in sensitive buildings, historic structures where there is doubt in the diagnosis, or as part of litigation.

Sampling
Due to the possible influence of hygroscopic salts, condensation and ambient humidity, the results of tests taken from surface plaster alone can be misleading. If doubt exists concerning a diagnosis or in case of dispute, indepth drilling and sampling below and at intervals above the damp proof course line may be necessary, with moisture content being assessed using either an oven drying or calcium carbide method.

Whilst the use of insulated probes with an electrical meter can help to eliminate interference from surface contaminants, the readings obtained can only be compared relative to each other and must therefore be interpreted with caution.

If samples are to be removed from site for laboratory testing, they must be stored in airtight containers to prevent any loss or gain of moisture in transit. In addition, an accurate record of the exact location for each sample is essential for correct interpretation of the results.

If an active electro-osmosis damp proof course is present within the wall under investigation, this must be switched off before tests are undertaken, to prevent erroneous results.

REMEDIAL ACTION ON DIAGNOSIS OF RISING DAMP
If the source of the dampness problem is identified as rising damp and it has been identified that this is due to the lack or failure of a damp proof barrier, a new damp proof course may be required. This can be in the form of a physical barrier, a chemically injected damp proof course, or in some circumstances an electro-osmosis system.

In most cases the deposition of ground salts will also necessitate the removal of areas of damp or salt-affected plasterwork. This will not in itself remove water and salt accumulation from the wall, which may continue to evaporate out over time. For this reason subsequent replastering must use materials resistant to the passage of residual moisture or salt in the drying wall.

Gypsum-based plasters are not usually recommended where walls have been affected by dampness or salt contamination.

Further information on the diagnosis and treatment of rising dampness in masonry walls please contact UK DAMP & DECAY CONTROL on 0800 028 1903

The recommendation of “Further Investigation” is frequently made by Surveyors and Valuers following surveys of domestic properties, often for mortgage valuation purposes. Unfortunately, the result of this recommendation is often to deliver the client into the hands of surveyors from remedial treatment companies, who usually have a sales commission incentive to specify as much remedial work as they can. The diagnostic evidence used to justify the various forms of remedial treatment is usually inadequate and much of the work carried out is, therefore, unnecessary.

Introduction to the Remedial Treatment Industry - Timber Treatment, Damp-Proofing and the 20-year Guarantee
The remedial treatment industry came into being in the UK in the period following the Second World War. At this time a number of companies established themselves to offer chemical pre-treatment of timber for use in the building industry, using preservation chemicals and techniques developed during the war. By the early 1950s, the industry had progressed to in-situ chemical treatment of timbers in buildings. The two major players at this stage were Protim and Rentokil, who both moved to embrace damp-proofing technology, within days of each other, in 1963. The gradual development of chemical injection technology, and the availability of a cheap, portable electric injection pump, brought a growing number of building contractors into the business in the late 1960s and early 70s.

There are currently estimated to be between 1700 and 2000 contractors offering remedial timber treatment and chemical damp-proofing in the UK, with an estimated turnover of between £200 million and £300 million. Around 200 companies, with some 300 branches, are members of the British Wood Preserving and Damp-Proofing Association (BWPDA), now incorporated into the Property Care Association (PCA).

The concept of the 20-year guarantee first arose, in respect of remedial timber treatments, in 1956, at the insistence of the building societies. This would appear to be a peculiarly British practice, brought about largely by the Caveat Emptor clause of the British legal process. In other European countries the buyer can demand rectification of hidden faults up to two years after purchasing a house. In Britain a guarantee is required. The 20-year length of such guarantees dates from that period, when 20 years was the usual mortgage term. The length of the guarantee was largely meaningless in 1956, however, since no company had anything like that length of experience in remedial timber treatment. When remedial damp-proofing was introduced in Britain in 1963, similarly 20-year guarantees were issued, although neither of the two companies concerned, Protim or Rentokil, had any length of experience in the field, and their respective damp-proofing systems - Protims Knapen tube and Rentokils Electro-osmosis - were unproven, and later discredited. The founder of Protim has expressed the opinion that, aided by the provision of local authority improvement grants, the whole success of the remedial treatment industry is due to the 20-year guarantee demanded by the building societies.

Prior to this period, problems with dampness and timber infestation were approached by attention to construction practice, ie. ventilation, isolation of vulnerable floor timbers from contact with masonry, use of porous lime plasters etc. A very real danger with the quick-fix chemical treatment approach is that it encourages householders and builders to think that poor construction practice can be rectified by chemical treatment. This is almost certainly not the case; timbers will only become affected by insect or fungal attack if they are damp; if you have damp timber and you drench it with chemicals then you end up with damp timber drenched with chemicals. In addition, timber treatment chemicals are toxic, and there are well-documented hazards associated with their use. Surveyors would be well advised to acquaint themselves with the potential dangers of timber treatment chemicals in case their recommendation should result in litigation.

Moisture Measurement in Masonry - the Myth of Rising Damp
The measurement of moisture content by electrical conductance methods has been widely used in various industrial processes, primarily those involving wood products and the storage of foodstuffs, particularly grain. Electrical conductance has also been widely used for the moisture measurements of soils, sand and aggregates. The earliest surviving documentation of the method dates from the 1930s, with much research material being published during the 1940s, 50s and 60s.

Nonetheless, before 1955 there does not seem to have been a portable moisture meter available specifically for use in buildings. In 1954 Protim, suppliers of chemicals for the pre-treatment of building timber, first became involved with the in situ treatment of timbers in buildings. In order to ascertain the presence and extent of dampness in the timbers one of the partners, Gerald Gobert, constructed a conductance meter using parts obtained from an RAF surplus shop. Some forty years later his brother, Ernest, told me that they always knew, from experience and visual inspection, when there was a dampness problem in a building being surveyed - the prime purpose of the meter was to impress the client, or local authority Sanitary Inspector, with the scientific nature of their equipment. This was the first Protimeter. In 1957 Protimeter Ltd was formed as separate company to manufacture and sell the meters.

Protimeter Ltd also began manufacturing meters for the measurement of moisture in agriculture and industry, but the current turnover in building surveying instruments alone is of the order of £600k - £750k p.a., representing several thousands of instruments being sold annually.

Since the 1970s, there has been a lively debate concerning the accuracy or otherwise of electrical conductance meters in the diagnosis of dampness problems in buildings, the main protagonists being Protimeter Ltd and the Building Research Establishment. Early BRS/BRE publications on dampness do not refer to the use of electrical moisture meters. However by 1975 it was being stated in BRE publications that ... the use of electrical conductivity meters in survey work does not allow for the correct diagnosis of rising damp, and that the only reliable way to measure moisture in a wall is by weighing and drying drilled samples. These sentiments found their way into the seminal Digest 245, in which it is stated.

The electrical meters commonly used by surveyors are responsive to both the amount of moisture present and to the salt concentration and are incapable of distinguishing between the two. Such meters quite commonly give high readings on the walls of old properties where some accumulation of salts inevitably occurs on internal surfaces. This does not mean, however, that the property necessarily has a dampness problem; high readings can be obtained from a wall where the concentration of salts is high, even if the wall is virtually dry.

A major source of confusion in the use of electrical conductance meters concerns their use on plaster and masonry materials, rather than timber. The meters are calibrated for use on timber, a material which does exhibit a certain direct proportionality between its moisture content and its electrical conductance. Timber, moreover, does not exist in buildings in a dry state - it has a certain cellular moisture content, ranging between approximately 5% and 25% depending upon species, use and environmental conditions. It is known that fungal decay does not occur in timber at a moisture content lower than 16% to 18%, measured by weight, so it was a fairly logical step to draw attention to this fact by accentuating this level of reading on the Protimeter dial, which is marked percentage moisture content. The problem arises when the Protimeter is used by a surveyor to test for dampness on the surface of a wall; the electrical conductance of the wall may well vary according to its moisture content, but the readings on the meter dial are not indicative of percentage moisture content, nor do they allow for the fact that they may be caused by surface condensation or the presence of salts.

Notwithstanding, the fact is that Protimeters are used by Chartered Surveyors and Remedial Treatment Surveyors almost exclusively in the diagnosis of dampness problems in buildings. Invariably the practice is to use the meter to test an internal wall surface - paint, plaster or wallpaper - and to interpret any reading near ground level as evidence of rising damp. The diagnosis of rising damp requires a much more detailed study, which Surveyors usually feel is beyond their remit. Unfortunately, the specialists whose services are subsequently called in are themselves no more knowledgeable, and are, moreover, concerned to gain commission by selling chemical damp-proofing.

Chemical damp-proofing
Chemical damp-proofing itself has an uncertain pedigree. Although it is theoretically possible to achieve a water-repellent barrier by the pressure injection of some of the variety of fluids on the market, research has shown that it may take injection times of up to 21 minutes per hole to achieve a satisfactory result. In that case it could take up to three weeks to pressure-inject a single house. In practice, the job is normally undertaken in a few hours.

Conclusion
Many Surveyors and Valuers assume that the subjects of moisture measurement and chemical damp-proofing are thoroughly researched and proven. In fact, these are both very inexact sciences, and the current dominance of electrical conductance-type moisture meters, and chemical injection damp-proofing, owe more to the marketing efforts of the damp-proofing companies than to independent scientific research.

There is no certainly no independent research that shows that large numbers of British houses are affected by ground water rising up into the walls by capillary action. Rising Damp is a myth.

For more information about impartial and independent damp surveys together with environmentally , chemical free, cost-effective solutions to rising damp please contact UK Damp & Decay Control on 0800 028 1903 or email enquiries@ukdamp.co.uk

Moisture meters are used frequently in surveys of buildings without professionals being specifically trained as to their capabilities or their limitations. It is therefore important to understand the limitations of the standard electric moisture meter to avoid misdiagnosis of rising damp:

The moisture meter is intended and calibrated for use on timbers, not masonry.
The percentage moisture meter readings in materials other than timber are not very meaningful
The temperature and relative humidity at the time of the inspection will strongly influence readings, and these can be highly variable.
The moisture meter cannot differentiate between moisture originating from capillary action, either rising or penetrating dampness, or from the presence of salts.
The readings are limited to surface readings.
The readings can easily be misinterpreted, as they can be affected by the presence of salts and/or past damp-proofing treatments.

Damp-proofing surveyors should exercise extreme care, particularly when interpreting meter readings on non-wood materials. An over reliance upon the results can lead to misdiagnosis and unnecessary damp-proofing work ;for this reason the interpretation of the readings needs to be based upon an understanding of the limitations of the equipment and of what is actually being measured. It is unwise to recommended damp-proofing treatment where the assessment has relied solely upon the results of a moisture meter; it should only be used as a tool to aid diagnosis, not as the sole arbiter that is unfortunately become.

The moisture meter can however be used to provide information and aid diagnosis in a positive manner that builds up a picture of the problems being investigated. For example:

Where no, or low, readings of dampness are found this can be a positive indication that the fabric is dry
Where high readings are found this indicates a problem that requires further in-depth investigation.
The moisture meter is calibrated to measure the wood moisture equivalent. This can be used to confirm the dampness of masonry by measuring the moisture content of timber in contact with the walls. This provides a more accurate picture of the level of dampness compared with relying solely on the moisture readings of masonry.
Plotting the moisture profile and distribution across the whole of a wall or areas identified as being at risk in a building will assist in identifying the potential sources of dampness and any timbers at risk of decay.

For more information regarding accurate, impartial and independent damp surveys please contact UK Damp & Decay Control on 0800 028 1903

Dry rot is the decay of wood caused by the fungus Serpula lacrymans, the effects of which in buildings can be truly dramatic. Diagnosis of dry rot in a building, like the diagnosis of cancer in a patient, has the ability to strike terror into the heart of the recipient of this dire news. However, all wood-rotting fungi require both food (wood or other cellulosic material) and water, and the dry rot fungus is no exception; deprived of either, it cannot survive.

Much of the mythology surrounding dry rot is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry areas and for the fungus to manufacture its own water. In reality, the delicate hyphae are the primary colonisers and the ability to conduct water is limited and can be negated by good ventilation. The process of wood decay itself produces water but in this respect dry rot is no different from any other wood-rotting fungus and, likewise, its ability to produce moisture in this manner can be negated by ventilation. Decay will cease if the moisture content of the wood is reduced to below about 20 per cent, and many extinct outbreaks of dry rot are discovered in buildings where the fungus has died out as a result of this happening, probably following maintenance which has eliminated a water source.

CONTROL STRATEGIES

Because of the total dependency of dry rot on moisture, the primary control strategy must be based on environmental considerations aiming to restore and maintain dry conditions. However, in many cases drying will take a long time, often measured in years, especially where some types of historic buildings are affected. Therefore, secondary measures will often be required to prevent further damage by the fungus before it is effectively arrested by the drying.

PRIMARY CONTROL MEASURES

A detailed survey should be carried out to identify and locate sources of moisture ingress. Particular attention should be paid to roofs and rainwater systems with emphasis on gutters and downpipes, parapet roofs and roof coverings. Rain penetration can also be through renderings and flashings or around windows and doors. Rising dampness through missing, bridged or otherwise defective damp-proof courses must be rectified. Any plumbing should also be inspected for leaks.

Rapid drying should be encouraged through the provision of heating and ventilation which may also require specific building work to prevent moisture ingress and transfer, and to encourage aeration. Dehumidifiers can remove moisture from the air but their effectiveness in aiding drying of walls depends on the rate of evaporation from the wall surfaces.

OTHER MEASURES
Assessing the outbreak
It is necessary to determine how far the dry rot has spread. All woodwork in the vicinity of any outbreaks should be inspected carefully to assess the extent of decay and the current moisture content of the timber. Extensive removal of plaster is necessary only if it is suspected that timber is embedded in the walls and is at risk.

Removing affected timber
Removal of all timber affected by dry rot is destructive but necessary in principle. Retaining affected timber presents problems for the structural integrity of the building and falling debris can be a hazard to occupants and others if decay continues. Timber already below 20 per cent moisture content presents little risk of further decay but, at higher moisture contents, the level of risk depends upon the speed with which drying can be induced and the ease of monitoring the reducing moisture content. Higher risks may be acceptable where timbers are of historic value or where their removal cannot be achieved without damage to important historic fabric - for example, where they support a fine plaster ceiling. In such cases the retention of some timbers may be essential or at least highly desirable.

If the wood can be removed, it can be sterilised in a kiln. The temperature throughout the wood must be maintained at just over 40°C for 15 minutes. Care is needed to prevent splitting and distortion and this method provides no protection to the wood after reinstatement.

Special building measures are necessary if timber is to be retained, including isolation from damp masonry.

Wood preservative treatments
Liquid preservatives can be applied to the surface of sound timbers left in situ to help prevent new infections developing during the drying process. However, they should not be used or regarded as an alternative to physical methods of protection.

If timber infected with dry rot has to be retained for special reasons and decay cannot be arrested in the short term by drying, preservative treatments that penetrate throughout the affected part of the timber can be used. For example:

• application of a preservative paste
• repeated addition of liquid preservative to sloping holes drilled into the wood or by pressure injection
• insertion of borate rods or tablets (these are only effective if the wood is wet).
Treatment of hardwoods must include an insecticide if there is a risk of infestation by death watch beetle.

All new timber used in repairs should be pre-treated with a wood preservative. Detailed guidance on the treatment required for various timber components is given in the British Standard BS 5268: Part 5, which deals specifically with structural timber, and BS 5589 which covers a wider range of uses. Guidance is also given on the use of naturally durable timbers (see also Digest 429 published by the Building Research Establishment Ltd).

MASONRY TREATMENTS

Although strands can grow through and across masonry, the dry rot fungus derives no nourishment from it. The concept of killing the fungus within masonry by wide-spread irrigation with a fungicide traditionally has provided a comfort factor, but it has to be questioned in each case whether this procedure can be justified. First, it is usually difficult to achieve a thorough treatment and, secondly, the treatments introduce large quantities of water which then need to be removed, increasing the risk of salt efflorescence and damage to the masonry, as well as prolonging the time it takes to dry the structure.

The most important role of chemical treatments of the masonry is to prevent the fungus from obtaining access to a fresh food supply in the form of timber in adjacent areas, or replacement timbers being introduced into the area. For this purpose, localised chemical treatments of the masonry can create a useful barrier between the fungus in the wall and the wood.

Examples of such treatments are:
• surface application of fungicidal fluid (which also helps prevent fruit-body formation during the drying phase)
• use of fungicidal renderings
• insertion of preservative plugs or pastes
• localised irrigation treatments.

Whilst these localised treatments play a role in the overall control strategy, they must not be regarded as a substitute for getting the building dry.

Heat sterilisation of masonry walls and timber in situ
In the past, the use of heat to sterilise walls was condemned because it was too difficult to apply effectively and provided no residual protection. In the search for chemical-free control measures, sterilisation with hot air is now increasingly being used, particularly in Denmark. However, the process needs to be carefully controlled so as to prevent damage to the building as well as to ensure that the necessary temperature has been achieved deep in the affected area.

MONITORING

The importance of monitoring the conditions in buildings cannot be over-emphasised. Dry rot develops very slowly, so early detection and curing of moisture ingress will prevent decay occurring in the longer term. Routine monitoring can be as simple as regular visual inspection to check the integrity of the building fabric against ingress of moisture, and taking measurements of moisture content of vulnerable timbers with a hand-held probe. However, sophisticated permanent monitoring systems are now increasingly used involving computer-based equipment linked to probes permanently installed in timbers or other parts of the building fabric. Specific sensors can also be installed in rainwater goods to indicate overflows.

Dry rot is potentially a cause of seriously damaging decay for timber in historic buildings, but it does not have to be devastating or outrageously expensive to cure if caught in time. A careful diagnostic approach is required to identify and cure dampness, to treat in a very selective and targeted way and to re-instate with appropriately pre-treated or naturally durable replacement timber. Installation of monitoring systems to facilitate routine maintenance checks can enable massive economies compared with destructive re-build approaches and will provide greater assurance for the future.

Recommended Reading
Building Research Establishment (BRE) Information Paper IP 19/88 House inspection for dampness British Standards Institution
BS 4072, Wood preservation by means of water-borne copper/chrome/arsenic compositions, 1987 (revised version to be published shortly) BS 5268 Code of practice for the structural use of timber Part 5: 1997 Preservative treatments for constructional timber
BS 5589 Code of practice for preservation of timber, 1989

BRE Digests
163 Drying out buildings
299 Dry rot: its recognition and control
304 Preventing decay in external joinery
307 Identifying damage by wood-boring insects
321 Timber for joinery
327 Insecticidal treatments against wood-boring insects
345 Wet rots: recognition and control
364 Design of timber floors to prevent decay
371 Remedial wood preservatives: use them safely
378 Wood preservatives: application methods
429 Timbers: their natural durability and resistance to preservative treatment

BRE Timberlab Papers
Dry Rot - Causes and Remedies, TP No: 44-1971 (Reprinted 1981)

Books
DH Jennings and AF Bravery (eds), Serpula Lacrymans: Fundamental Biology and Control Strategies, John Wiley & Sons Ltd, Chichester, 1991
For further information contact BRE, Garston, Watford WD2 7JR
Tel 01923 664000 Fax 01923 664010 E-mail GrantC@bre.co.uk

Overview
In spite of the recent media hype over the presence of mould in residences and the workplace, there is virtually no scientific or medical data that supports the level of fear and concern generated by misleading and sensationalized news reports.

All houses, offices, and workplaces have mould. All houses and workplaces contain the dreaded “toxic black mould” (a nonsensical term invented by the news media). Virtually every human, in virtually every location on earth inhales hundreds to hundreds of thousands of mould spores and mould fragments on a daily basis. And yet, contrary to common belief, there is currently no evidence that the presence of these moulds and the exposures to the same poses the threat to the health of members of the general public as suggested by irresponsible journalists, and dramatic news reports largely devoid of objective facts.

Ignoring for a moment that virtually all “mould tests” and all “mould samples” are completely invalid, and uninterpretable and cannot be used for decision making, indoor moulds almost always get the initial blame for complaints about indoor air quality. However, in the Summer of 2011, the US Department of Labor, OSHA published the guidelines “Indoor Air Quality in Commercial and Institutional Buildings”, wherein OSHA referenced the Indoor Air Quality Investigation protocol in its Technical Manual and points out that all microbial contaminants combined (including viruses, fungi, mould, bacteria, nematodes, amoeba, pollen, dander, and mites) were found to be the primary sources of indoor air quality problems only 5% of the time. The unwarranted fear is propagated by a variety of “mould remediators” and “mould inspectors” who usually have no legitimate knowledge in mould or mycology but prey off the public’s fear and perform nonsensical and invalid mould “testing.”

In July of 2009, the World Health Organization (WHO) published its position paper 2on indoor moulds and Indoor Air Quality. Contrary to what many people in the mould remediation business want to believe, the WHO guidelines reinforced the findings of the 2004 Institute of Medicine mould study group. In that study, the IOM stated there was insufficient evidence to find a causal association between the presence of moulds and any of the claimed adverse health effects. That is, after reviewing the global scientific and medical literature, the IOM could not find sufficient evidence to support the argument that the normal presence of mould in residences and workplaces caused any adverse health effects.

These findings are consistent with other notable organizations, such as the “Health Alert” published by University Health Publishing and John Hopkins Medicine who state: 3

Popular reports about the health effects of muold are likely to include the term “toxic mold.” But that term can be misleading, the experts say. They point out that only certain muold spores produce toxins, and only under certain circumstances. Just because a particular mould can produce toxins doesn’t mean it will. Even if the mould is producing toxins, a person must breathe in a sufficient dose to be affected. It is highly unlikely that you could inhale enough mould in your home or office to receive a toxic dose.

The WHO and the IOM, however, both concluded there was an association between damp living spaces and some adverse health effects. The unfounded assumption by those unfamiliar with the studies presume that mould was responsible for the association, however, this is not the case. Although it is well established that there exists an “association” between damp in buildings and a slight increase in observed adverse health effects, it is also well established that no one has been able to conclusively demonstrate that the association is exclusively due to the presence of mould. WHO and the IOM note that dust mites, Bacteria, termites, protozoans, endotoxins, VOCs, formaldehyde, pesticides, viral survival and generally poor ventilation are similarly associated with damp, and these factors, too, are considered to be part of the etiological backdrop. As such, in the remediation of water damage, the stress is placed on correcting “damp” and not on removing mould.

The common misconception is that when water damage occurs, and/or mould is found to be present, it is imperative to find and remove the mould. However, this position is promoted mostly by companies who make a living from removing mould (including “hidden” mould), and therefore, the more mould they remove, the more money they make! Otherwise, there is no compelling reason to do any remediation beyond correcting the water damage, and (as part of that correction), address any remaining visible mould. The notion that “hidden mould” presents a significant threat to human health or the quality of indoor air, is a myth. All studies performed to date have demonstrated that mould hidden in walls, do not adversely impact the air quality in the occupied space.

Indeed, leaving mould contaminated surfaces inside a property following a remediation is not only unavoidable, it actually constitutes part of the decision making process incorporated in such texts as the so-called “Green Book” 4 and the WHO study, wherein WHO states:

The main challenge of field investigations is to decide which contaminated materials should be removed and which can be left in building assemblies with a reasonably low risk of indoor climate problems.

Far too many homeowners and property managers spend needless thousands of dollars of wasted financial resources unnecessarily tracking down and eliminating mould under the misconception that such removal is standard practice and is necessary to ensure good indoor air quality. In general, the removal of mould is considered to be acceptable when it is limited to that which is visible and/or known to be present and constitutes a problem due to aesthetic considerations. In general: 5

However, removal based on the mere fact of its presence, or based on nonspecific symptoms that are not related to muold exposure, is often not appropriate.

Similarly, other notable researchers have also concluded the same: : 6

…it is reasonable to infer that small amounts of mould enclosed in walls, floors, or ceilings will not have a large impact on the indoor air quality.

Studies and investigations performed by this author (Connell), consistent with other researchers, have not observed a correlation between mould hidden in walls and a degradation of indoor air quality or a correlation between mould hidden in walls and an increase in spore counts in occupied spaces.

Finally, we have encountered several poorly trained remediators and “mould consultants” who claim they need to find the hidden mould to pass the “final clearance sampling tests” following a mould remediation project. However, in short, there is no such thing as “clearance testing” for moulds. No such tests, as commonly conducted, are scientifically valid, and none stand up to scientific scrutiny. The “Green-Book” for example, addresses “final clearance sampling” thusly:

18.5.2 Current mould remediation guidelines support the concept that project success depends on verification primarily through inspection that visible mould growth and associated debris and dust were appropriately removed. 7, 8, 9

The AIHA publication continues with:

The primary objective of mould remediation, based on based on guidelines published between 199310and 200411, 12 is to remove visible mould growth and return material surfaces to a satisfactory condition.

And the section concludes with:

A difficulty associated with using air sampling as the primary means of achieving final clearance is the absence of numerical guidelines for airborne fungi and for bioaerosols in general. 13, 14, 15 IOM16,concluded that, although there is an association between respiratory health effects and dampness, the exact causal agents of irritation and respiratory disease are obscure. Thus, from a health effects viewpoint it remains uncertain whether the EHS investigator should sample during final clearance for total spores, culturable spores, hyphal fragments, specific allergens, glucans, endotoxins, or other agents.

Dry rot is a destructive fungus whose history and name has left a legacy of confusion. Many still consider any brown, cuboidally cracked decay to be dry rot, and the inference from the name that dry rot needs less water than wet rots has had disastrous consequences for a number of buildings and the finances of their owners.

Dry rot is essentially a very efficient brown rot decay fungus with quite specific environmental requirements, but it has a reputation as a house-destroying superorganism. Much of the exaggeration and confusion concerning dry rot stems from the rather poor use of common names used to describe building fungi.

There are four terms in which building decay fungi are often described:

• Dry rot. In the UK this is a common name applied to one species of fungus only:Serpula lacrymans. It is sometimes applied to Meruliporia incrassata in North America.

• Wet rot. This is a catch-all term for every species of fungus that is not Serpula lacrymans.

• Brown rot. This term describes the mode of action of the fungus. In this respect, the term has some scientific relevance. Brown rots decay timber leaving the wood brown.

• White rot. In contrast, white rot fungi leave decayed wood white.

Dry rot (S. lacrymans) is a brown rot. Wet rots may use either mode of decay.

It is unfortunate the use of the terms dry and wet rot are so ingrained in the literature of building decay fungi as they are poor and misleading descriptors of these organisms. A brief overview of the history of building decay fungi in the UK reveals how we arrived at this unfortunate situation.

The origin of Serpula lacrymans in the British Isles remains obscure. The fungus does not occur outside of buildings over most of its range across the temperate regions of the world with the exception of a few colonies from the Himalayas, East Asia and the Czech Republic. Recent research has shown that two sub-groups of of the fungus exist, a wild type predominantly found in North America at high altitudes, and a more aggressive variety possibly of Asian origin.

It seems logical to suppose that dry rot reached these shores in infected timbers from Europe and the lack of genetic variation in the variety seems to support this. We know that the fungus attacked softwood on ships, and we also know that fungus had frequently to be scraped off cargoes of softwood when they were landed. Many cargoes of timber from the New World and from Europe had been largely destroyed in the ships holds before they reached port.

In 1759 shipbuilders along the Thames were asked to give an opinion on the comparative durability of English and French ships. They concluded that the English ship of war should long outlast the French. By the beginning of the nineteenth century, however, the situation had reversed. Matters came to a head in 1810 when the second HMS Queen Charlotte was launched at Deptford. Close examination revealed that all her upper-works (ends of the most of the beams, carlings, and ledges, the joinings of the planks etc.) were infected with the dry rot. The situation was investigated by A. Bowden of the Navy Office who published his conclusions in 1815 under the title -A Treatise on the Dry-Rot.

Two main forms of timber decay were recognized in Bowdens day, and these were common or wet rot and a relatively new phenomenon they called dry rot. We still use the same terms but our meaning is rather different, and it is important that we understand this difference.

In the eighteenth and early nineteenth centuries wet or common rot was seen as a form of decay which progressed inwards from the surface of the timber and was caused by the actions of wind, heat and water. The damage was thought to be chemical or mechanical. The resulting modified timber was considered particularly suitable as a substrate for fungus.

The connection between the dry rot and water was not made for a long time because the decay was seen as progressing from the inside of the timber outwards. The concept of water being absorbed and held within timber resulted in fungal decay was not grasped until later.

It is clear that what the earliest investigators termed ‘dry rot’ was in fact brown rot, and common or wet rot was white rot. The application of two different names is understandable when we consider that the two forms of decay do not look alike, and progress in a different fashion. The term was used because the damage was thought to be caused by internal ‘fermentations’ rather than water. It is also important to note that the term ‘dry rot’ was used for all brown rots, and would therefore have encompassed a wide variety of fungi which we would now consider to be wet rots (e.g. cellar rot).

The fact that fungi caused the decay rather than just living on it was not firmly established until work by the German botanist Robert Hartig was published in 1878, although the suggestion had been made as early as 1803. Considerable research into decay fungi ensued, not all of which was relevant to practical building situations. The conclusions reached, however, stay with us and have been woven into the mythology of dry rot.

Gradually throughout the nineteenth century the term became restricted to fungi which produced substantial mycelium, and even during the first half of the twentieth century there was a tendency to include the mine fungus Antrodia (Fibroporia) vaillantii as a dry rot. Eventually, however, the name referred to only one fungus Serpula lacrymans, and this became known as the ‘true dry rot’. All other decay fungi (brown and white rots) were lumped together as wet rots. The ‘true’ prefix was gradually dropped towards the end of the twentieth century, although some literature still cites it as such.

The term ‘dry rot’ has come a long way from describing the fermentations of sap in eighteenth century ships’ timbers. Work undertaken by the Forest Products Research Laboratory for the production of a British Standard in 1963 perceived the difference between wet rots and (‘true’) dry rot was that the strands of dry rot had the ability to grow through walls and over inert surfaces. In contrast, the strands of wet rots (those that produced them) did not. Dry rot could therefore spread through the building where conditions allowed, whilst wet rot decay remained localised.

This is not the case: many species of wet rot will grow over or through walls. However, the separation of S. lacrymans from other building decay fungi and from other brown rot fungi has resulted in its inadvertent and quite unfounded status as a unique organism capable of quite the most biologically impossible feats. Coupled with a commercial treatment industry that is only too happy to pander to this unabashed scare-mongering in order to sell fungicide it has come to be feared by homeowners up and down the country.

Water damage in buildings and the prospect of timber decay

Should timber decay be expected without question, and what can be done to minimise the risk?

The following popular, but quite erroneous, wisdom has arisen from investigators’ unquestioning but misinformed belief that the fungus has a name that accurately describes its biology, namely that:

• Dry rot produces enough water from the wood it is decaying to sustain it, so that the fungus continues to spread and cause damage even if the source of moisture that caused it is removed.

• Dry rot strands conduct water to make dry timber wet enough to attack.

• Buildings dry through a moisture zone where there is a risk of dry rot developing.

All of these ideas are nonsense, but widely believed and the consequence has been massive destruction. The treatment of dry rot has usually caused far more damage to our building heritage than the fungus. There are several archival cases where stately homes have been demolished due to financially prohibitive dry rot treatment quotations.

There is no doubt that dry rot, growing in a damp and neglected building, can cause considerable damage, but it will still be restricted by the local environment. A dry rot spore needs to land on timber with high moisture content (in excess of 28%) in order to germinate. Once growing, it will not spread to the dry parts of the house, a fact recently described by a German researcher, Tobias Huckfeldt, who also found its growth rate to be comparable to that of other building fungi. The fungus needs a substantial amount of fresh water to grow and thrive. Without that, it poses no threat to a building. Such potential sources of water should be considered before any suspended floor deemed insufficiently ventilated has the walls supporting it riddled with airbricks (with more loss of the building fabric).

‘Dry rot’ as a term to describe Serpula lacrymans is an unfortunate and inaccurate legacy of 200-year-old observations misapplied to an organism that does not warrant the infamy it has achieved.

The aims of this information sheet are to encourage the prevention and control of timber decay in old buildings by appropriate repair and regular maintenance by providing a step by step approach to timber defects. Many old buildings have been subjected to unnecessary, damaging chemical timber treatments. The most common reasons for this are:

The misdiagnosis of insect infestation and fungal decay.
The misunderstanding of the significance and structural implications of decay resulting in drastic remedies being used to deal with minor or extinct problems.
The carrying out of inappropriate or excessive treatments by timber and damp specialists as a condition of a mortgage.
The pressure to obtain instant and single solutions with guarantee backing ( as required as a condition of a mortgage)
Some remedial treatment companies having a tendency to recommend works in which they have a financial interest.
Some remedial treatment companies specifying more work than is necessary to minimise the risk of claims on guarantees.

The Step by step approach to avoiding unnecessary treatment

Step 1- Commission and inspection by someone with appropriate specialist knowledge.
Decisions about what, if any, timber treatment is appropriate should be informed ones, based on a careful inspection of the building. The assessment needs to be made by someone who understands the type of construction likely to be encountered, the timbers used in the construction, and the types of timber decay organisms that can attack the timbers.

Step 2- Careful assessment of the problem
This should include the following :
Detailed inspection of the timber defects-looking for signs of problems; probing accessible timbers to test their resistance; sounding timbers with a hammer for hollowness; testing with a moisture meter. The moisture meter is only a tool to aid diagnosis- its readings need to be interpreted by a person who understands the limitations of this equipment and what it is actually measuring- and must not be relied solely upon when deciding treatment. Identification of the causes and types of decay-dry timber is not vulnerable to attack by fungi or insects; they can only cause serious damage when there is damp. The first stage is to identify and eliminate the source of dampness otherwise the decay problem will continue.
The surveyor must understand the relationship between timber type, conditions within the building and decay organisms:-
The extent of damage and its structural significance.
The activity of the decay-decay that appears serious may be an extinct outbreak.
Is there a need for maintenance and/or further investigation? The more information available on the type and extent of the problem, makes possible the correct repairs and treatments. Thus the extra time and money of further investigation/monitoring is usually outweighed by the gains in avoiding necessary treatment.

Step 3- Implementing the repairs
Once the extent of damage and decay has been ascertained, appropriate repairs can be initiated. Achieved by :
Eliminating the sources of dampness
Controlled drying of the fabric.
Repairs to reinstate the structural strength of the timbers and the construction.
Providing support features-ventilation/isolation of the timbers.
Monitoring.

Step 4- Is timber treatment really necessary?
A sound basis to start from is the Health and Safety Executives recommendation that – we must always seek to solve timber problems by construction methods (such as repair and replacement) where economically viable, before considering the use of chemical treatments.
The understanding of the building gained in Step 2 provides the information fro making a positive, well-informed decision on the most appropriate action for the building; whether the problems identified can be resolved by traditional construction methods of repair or whether chemical timber treatments are really necessary.

Any chemical treatment must be justified, targeted and applied in accordance with controlling regulations and legislation (Control of Substances Hazardous to Health 1988 (COSHH), Health and Safety at Work Act 1974, Control of Pesticide 1986, Wildlife and Countryside Act 1981)

Step 5- Implement regular and appropriate maintenance- the key to preventing future problems with timber decay.

If there is any doubt or concern about the advice or recommendations made regarding the repair or treatment of an old building, seek independent specialist advice or contact the SPAB.

Article originally published in the RICS Building Conservation Journal (No. 13 Winter 1995).

In the following article Richard Oxley expresses his concern over the increasing levels of uncontrolled and unnecessary remedial damp and timber treatments that a large proportion of historic buildings are subjected to. He identifies the problems and attempts to provide some solutions.

Introduction
Two examples of uncontrolled and unnecessary remedial damp and timber treatment are reviewed below together with some of the issues they raise. It is hoped that within the limitations of this article that I can convey the seriousness of this problem together with some of the items that I strongly believe need to be addressed.

Examples
The examples provided are both Grade II listed and typical of many historic buildings, in that they are of a vernacular construction; they are vulnerable to the impact of uncontrolled and unnecessary remedial treatment; and they do not have access to any significant resources, either in the terms of expertise or financial support, to be able to implement appropriate and sympathetic repairs. For example, English Heritage grant aid is aimed at the important Grade I and 11* listed buildings. These are the buildings which, in most cases, are already well protected and controlled and also have access to funding. The lack of resources available to the majority of listed buildings, combined with other external pressures and influences (such as the demands of the purchasers/owners for instant solutions; the requirements of mortgage lenders; the vested financial interest of the remedial contractors) leads to a significant loss of historic fabric. Uncontrolled and unnecessary remedial treatment can be shown in the examples below, and have played a prominent role in causing irreversible damage to historic buildings.

Example 1
A report from a remedial damp and timber contractor was provided on a late 17th century timber framed Grade II listed cottage. The causes of dampness to the building were positively identified by the contractor as defective rain water goods and high external ground levels. The contractor, however, stated that rising damp appears to be due to the apparent absence of an effective damp­proof course. As a consequence the provision of an injection damp­proof course and the removal of the existing floor were carried out.

A chemical damp­proof course was injected into the timber sill beam which was a complete waste of time, effort and money. To add insult to injury the contractors recommendations included providing an internal barrier of sand/cement render ... to those areas at least up to the level of the newly installed damp ­proof course. This would result in a sand and cement render abutting the injected timber sill beam, consequently trapping moisture and leading to the accelerated deterioration and failure of a principal structural component.

The contractor recommended the replacement of the existing floor with a modern concrete floor incorporating a damp­proof membrane. This would actually lead to exacerbating the problems of dampness within the building. The provision of this modern floor would remove a means where moisture could currently escape through evaporation. The consequence of this is that moisture will seek to be released via the walls, the hydrostatic pressure and capillary action causing a new damp problem. The historic fabric suffered severe irreversible disruption to facilitate the provision of the concrete floor.

In this case there is sufficient evidence to indicate that the inspecting remedial surveyor/contractor did not even have a basic understanding of the constructional nature of the building in question. As a result, standard treatment and practices have been carried out to a non­standard building. The dampness could have been eliminated through other methods, such as reducing external ground levels and repairing rain water goods. In combination with a lack of appropriate knowledge there would also appear to be evidence of implementing the standard remedial works (eg injection damp­proof course and re­plastering) ­ as the contractor had the available in­house skills and materials to make this cost effective and assist in his achieving any financial targets. It can therefore be argued that the lack of knowledge and the vested financial interest of the contractor have resulted in works to a listed building which cannot be fully justified, are totally inappropriate, and have caused a vast amount of irreversible damage.

- Example 2
Prior to the sale of a Grade II thatched timber framed building the vendor commissioned a report from a remedial damp and timber contractor. The contractor stated that a survey for rising dampness and a timber inspection of accessible timbers had been carried out. A subsequent inspection by a chartered surveyor for mortgage purposes revealed that in this case the causes of dampness had not been positively identified by the contractor, such as poor detailing between the thatch and chimney stack resulting in water penetration at both ground and first floor levels. In addition the contractor gave no warning about the potential for rot to exist or develop behind timber panelling ­ even though the levels of dampness identified by the contractor justified the provision of a chemical injection damp­proof course, into what is mainly a single skin timber framed building. The contractors recommendations were based solely on tests with a moisture meter and no tests were taken for the presence of salts. This did not stop re­plastering being recommended due to dampness from hygroscopic salts which absorb atmospheric moisture.

As mentioned, the brief inspection for mortgage purposes revealed the failure of the contractor to identify severe rot to a timber wall plate and rafters, caused by the poor detailing at the junction of the stack and thatch covering. This is a serious omission by the contractor due to the structural nature of the timbers involved. The contractors inspection and resulting recommendations show a blatant disregard for the recommendations of the Health and Safety Executive in their guide: Remedial Timber Treatment in Buildings. This guide clearly recommends that any inspection should identify the location of the sources of moisture; ingress of moisture into buildings is the main cause of damp timber and therefore fun gal attack. The surveyor must examine the whole building rather than just those parts obviously affected by damp.

In this case the cause of the damp penetration was identified by the mortgage valuation surveyor. This lead to an investigation of the areas at risk internally which showed that the mortgage valuation surveyor had followed the trail. Even within the limitations of a mortgage valuation this serious fault was positively identified, whereas it had been completely missed by the remedial contractor who had reputably inspected all accessible timbers.

This re­emphasises the recommendations made by the Health and Safety Executive in their guide; serious timber problems can be caused by more subtle failures in the building fabric, detailed survey must only be carried out by a qualified surveyor who has had appropriate and professional training in identifying building faults. There is no definition of a qualified surveyor within the guide but it can be assumed that a chartered surveyor would meet this requirement. At the very least it should be ensured that the inspecting remedial contractor has the Certified Surveyors in Remedial Treatment (CSRT) qualification, and, where possible, a knowledge of the physical and philosophical demands and requirements of historic buildings.

In this example, timber treatment was recommended by the contractor as a precautionary measure. The contractor did not identify and report any active infestation, only that there was evidence of previous common furniture beetle infestation. No justification for the recommended treatment was provided, thereby clearly ignoring the guidance of the Health and Safety Executive; The single most important question that must be asked by a surveyor is, is there any need to use wood preservatives to control and stop timber decay? It is evident that the potential health and safety considerations of the occupiers/users of this building have been overruled by the short term commercial gains that can be made by the contractor following the practice of treatment.

As a result of the findings of the mortgage valuation surveyor, a subsequent inspection and report from another contractor was obtained. The results of which caused great concern because exactly the same errors and mistakes were made by the second contractor. Reiterating that many remedial damp and timber contractors are not geared up to propose appropriate remedial repairs and treatments to vernacular historic buildings.

These two examples, which from my experience are not isolated cases, illustrate that great care must be taken when relying or commenting upon reports and estimates from a remedial damp and timber contractor. It is essential to ensure that the recommendations made by the contractor are appropriate to the building in question. There is a tendency for surveyors to accept the recommendations made by the contractor as being automatically appropriate and justified. The examples clearly show that this is not always the case. It is important for surveyors to appreciate that their reputation as a property professional will diminish if there is a continued reliance in contractors who have a vested financial interest in their own recommendations. If chartered surveyors adopted this approach it would be considered unacceptable from an ethical point of view by the RICS yet this is accepted as standard practice for the remedial treatment of damp and timber decay in buildings.

Practice should be reviewed with the long term interests of historic buildings and the reputations of both the surveying profession and the remedial damp and timber treatment industry in mind.

The Effectiveness of Existing Controls
Remedial damp and timber treatment in historic buildings is mainly controlled on a discretionary basis. Whether listed building consent is required for remedial treatment is subject to variable levels of interpretation by different Local Authorities and their Conservation Officers. The political will of the individual Authority and the resources available to the Conservation Officer (in respect of available time and finance) may well influence whether or not listed building consent is actually required for such remedial treatment or not. As a result, a significant amount of treatment is carried out on an inconsistent, uncontrolled and unjustified basis. This results in a substantial amount of unnecessary damage to a significant number of historic buildings. For this very reason there is a strong argument for listed building consent being made a mandatory requirement where such remedial treatment is thought necessary. This would result in an increased level of consistency, control and justification over and above that which currently exists

On a strict interpretation of the guidance provided by PPG15 listed building consent should be required in the majority of cases where remedial treatment is proposed. There are sufficient examples to illustrate that there is a substantial amount of work undertaken during remedial repairs that would affect the character of listed buildings. If only the guidance contained within Annex C (C.3) of PPG15 was followed when remedial damp and timber treatment was being carried out then a significant amount of reversible damage would be avoided:

Alterations should be based on a proper understanding of the structure. Some listed buildings may suffer from structural defects arising from their age, methods of construction or past use, but they can still give adequate service provided they are not subject to major disturbance. Repairs should usually be low­key, re­instating or strengthening the structure where appropriate; such repairs may sometimes require listed building consent.

Conversely PPGI5, the principal guidance document concerning the protection of historic buildings, does not positively recognise the issue of uncontrolled and unnecessary damp and timber treatment. Annex C of PPG 15 addresses in great detail the external and internal constructional elements and how alterations to listed buildings should be approached. There is no mention whatsoever of remedial damp and timber treatment, arguably one of the most common as well as intrusive and destructive forces that can be inflicted upon historic buildings. This omission shows a complete disregard and a lack of recognition of a serious reoccurring problem.

The first example illustrated that inappropriate and uncontrolled treatment can lead to the structural integrity of the building being put at risk. This example is not an isolated case and as such this issue needs to be urgently addressed in a practical manner, so that the continued uncontrolled and unnecessary loss of historic fabric can be abated.

However, it seems highly unlikely that this issue will be adequately addressed as the current Government is attempting to introduce more democratic and relaxed controls within the imminent Green Paper. The buildin2s that are most likely to suffer from the implementation of such a proposal are those already susceptible and vulnerable to uncontrolled and unnecessary repairs and treatment, eg Grade II listed buildings of a vernacular construction; in fact there is a strong argument for tighter controls over the most basic of repairs such as re­pointing, the application of non­permeable paints and treatments, and re­rendering, in addition to remedial damp and timber treatment. In fact, it is these every day repairs and maintenance works that are contributing to the accelerated deterioration of the fabric of these buildings, probably at a faster rate than most of these buildings have suffered in their previous and long history. For this reason alone there is some justification for imposing stricter controls upon listed buildings as the current system is obviously failing the buildings that require the most protection.

Funds need to be made available to counter the lack of resources and also enable controls to be enforced. This could be achieved by allocating a pool of funds which could be made available from the Heritage Lottery Fund. Funds could be directed at the buildings that are currently the most susceptible to such uncontrolled and unnecessary treatment. Just a relatively small amount of money will enable Conservation Officers to exert greater control over the repair, maintenance and modernisation of these buildings and also provide owners with an increased incentive to repair their buildings in an appropriate and sympathetic manner. Thereby substantially reducing the vast amounts of historic fabric which are currently being lost through this uncontrolled practice.

The actual level of physical disturbance can be shown to be ineffectively controlled. This can be illustrated to best effect by using the chemical damp proof course, and the hard cement replastering that usually follows, as an example. The provision of a chemical injection damp proof course does not require any approval or consent and can be implemented at the whim of the contractor, who as we have seen may well have a vested interest In carrying Out the works. This makes the control of such work to historic buildings through the planning legislation (The Planning (Listed Buildings and Conservation Areas) Act 1990) even more important thereby vindicating the stricter control of damp and timber treatment by requiring such works to obtain listed building consent.

There is definite legislative control on the type of chemicals that can be used and how these chemicals can be used (Control of Pesticides Regulations 1986 (CPOR), the Health and Safety at Work etc. Act 1974, The Control of Substances Hazardous to Health Regulations 1988, the Wildlife and Countryside Act 1981. the Water Act 1989 and the Environmental Protection Act 1990). However, there is no express control that would actually reduce the levels of uncontrolled and unnecessary remedial treatment. The Health and Safety Executive guide provides enough ambiguity for the remedial contractor to justify treatment, as the guide recommends that wood preservatives should not be used unless it is judged necessary to halt an attack now or in the future The second example illustrated that the contractor made little or no effort to determine whether the infestation was active, yet the contractor still recommended treatment. From my experience it is not rare for the contractor to recommend treatment without having ever determined whether the infestation was actually active or not. This is in conflict with the Health and Safety Executive guidance; The surveyor must attempt to establish whether the attacks are extinct ­ and if they are, treatment is not necessary.

Unless the contractor is conservation and/or environmentally minded then it is highly likely that treatment will be justified on the basis that it will be required in the future. Commercial gain will take precedent over the correct use and general principle of the guidance, which is for treatment to be implemented only where necessary. This is a problem that will be difficult to address within the confines of current practices and procedures. Therefore remedial contractors must be given every encouragement to be included within the field of conservation so that historic buildings can benefit from their participation and receive appropriate treatment where necessary. But remedial contractors must, however, show a clear and full understanding of the needs and requirements of historic buildings for their involvement to be justified.

Can the problem of uncontrolled and unnecessary treatment be addressed?
The obvious solution is for this problem to be resolved through the provision of increased resources, in the form of expertise and finance. But in these times of reduced budgets and strict control over financial expenditure it is highly unlikely that the necessary resources will be made available to enable the protection of these buildings to be improved. There needs to be an appreciation that unless this issue is effectively addressed the less important historic buildings that provide a back drop to our national heritage will continue to be at great risk. Without these buildings the more important Grade I and 11* properties will loose their historical background and context, which in turn would reduce our understanding of these buildings over time. For this reason alone there is an urgent need for a change in priorities so that the majority of historic buildings are given an effective means of protection. Recent research has lead to the development of sophisticated investigative, remedial and monitoring techniques and the development of an environmental approach to damp and timber defects. Currently the majority of historic buildings do not have the benefit of these techniques and these are the very buildings that are crying out for such remedies. The main reason for this is that a number of these techniques and methods are beyond the resources of these buildings and their owners, either in terms of availability, practicability, cost, expertise and/or funding. There is also room to improve the promotion to these products and techniques so that they can be recommended and/or used by the investigating surveyors and contractors.

On this basis there is a good argument for further research to be carried out to determine whether these methods can be adopted and/or developed so that they maybe easily implemented in an inexpensive manner utilising readily available expertise and materials. For any treatment to be to the benefit of the majority of historic buildings it has to take into consideration that the vast majority of these buildings are residentially occupied. There is therefore a need for these techniques to be developed so that they can be applied under these circumstances.

The majority of historic buildings will not benefit from improved practices until surveyors improve the level of their knowledge and implement their recommendations accordingly. It is not sufficient to identify that a property is suffering from damp and timber defects and then recommend that a report is obtained from a specialist contractor; this normally results in the whole process of uncontrolled and unnecessary treatment being instigated. There is a need to break this cycle if we are to avoid the continued loss of the historic fabric. However, current practices and procedures limit how a surveyor can report upon damp and timber defects, especially within the confines of an inspection and report for mortgage purposes. There is a need for more readily available alternatives to enable a surveyor to recommend that an independent specialist in historic buildings and/or damp and timber defects can be instructed to report upon the property. This would be in keeping with the mandatory recommendations of the Appraisal and Valuation Manual (the new Red Book) at Annex A to Practice Statement 9 which states at 3.10 that;

Where the Valuer decides to report a necessity for works to be carried out to a property as a condition of any advance and the Valuer identifies the property as being: ... of architectural or historic interest, or listed as such; or... in a conservation area.., the Valuer should advise that a person with appropriate specialist knowledge be asked to give advice as to the appropriate works unless, exceptionally, the Valuer believes he/she is competent to give advice which if adopted would not be detrimental to the propertys architectural or historical integrity, its future structural condition or conservation of the building fabric.

A significant number of historic buildings, being residential, will therefore be subject to a mortgage loan. The complex influences and pressures placed upon historic buildings by the mortgage process mean that it is essential that the correct persons are instructed to inspect and report on these buildings. This means that lenders and surveyors have to make every effort for the recommendations of the Appraisal and Valuation Manual to be followed. If this could be successfully achieved it would be a significant step towards substantially reducing the level of uncontrolled and unnecessary remedial treatment suffered by historic buildings. This is currently the aim of the Building Conservation Skills Panel Working Party which is looking at the relationship between mortgage valuations and historic buildings.

Summary
The basic philosophical principles that should be applied to historic buildings of maximum retention of early fabric, minimum intervention and maximum reversibility can not be adhered to when uncontrolled remedial damp and timber treatment is carried out. If this dichotomy persists and is not addressed a substantial amount of historic fabric will continue to be lost for no other reason than inertia and commercial gain.

On the basis of the arguments and examples put forward in this article there is an urgent need to; 1-formally illustrate that current processes and methods are acting to the detriment of historic buildings;
2-determine whether damp and timber defects can be resolved in a practical manner that can be put into everyday use;
3- identify what influences uncontrolled and unnecessary remedial treatment and how these influences can be addressed, and;
4- assess the implications of chemical treatment upon historic buildings both technically and environmentally.

Damp rises, penetrates, or results from condensation or leaking services. Rising damp is the most commonly misdiagnosed and remedial solutions for it are often inappropriate.

The term ‘damp’ is broad and the problems associated with damp in buildings can manifest themselves in various ways according to the source of moisture. damp can be a very emotive issue for property owners as the results can be both damaging to the fabric and decoration of the building, and may create an unhealthy environment for the occupant. The problem could also lower the value of the property.

When the term damp is applied to a building it suggests the presence of an unacceptable level of moisture within the building fabric. The source of moisture ingress associated with dampness falls into four broad categories, rising damp, penetrating damp, condensation and leaking services. Of the four sources of damp, it is rising damp that is most commonly misdiagnosed and for which inappropriate remedial solutions are recommended within historic buildings.

When faced with damp in a historic building, the first step generally taken by owners and, surprisingly, some historic building professionals is to call in one of the many local damp specialists. Such companies are often referred to as remedial firms or, perhaps more ironically in some cases, preservation firms.

Much of the remedial industry’s concerns installing remedial damp-proof courses and waterproofing (tanking) basements and other subterranean structures. Many operatives within the industry legitimately receive a sales commission on materials or contracts.

The problem for us conservation professionals is that the advice given by such firms is often inappropriate for historic buildings. However, the possibility of offering a more appropriate solution often requires a robust independent diagnosis. Commissioning such a diagnosis generally proves to be financially unattractive to the property owner and beyond the means of the conservation professional. It may be possible to compel a property owner to commission a second opinion from a consultant capable of working with historic buildings in cases where the building is listed and the remedial work would require listed building consent.

Rising damp is caused by moisture rising up from the ground by capillary action through interconnecting pores within the material. Problems can appear in floors and the base of walls up to about 1.5m above ground level. The visual evidence of rising damp is a band of discolouration or surface damage running around internal walls, usually about 500mm to 1m above ground level. The band, often called the evaporation zone, is caused by soluble salts migrating up from the soil with the rising moisture concentrate (on or within the surface of the substrate) and crystallising as the moisture evaporates. The expansion of the microscopic crystals within the material’s surface pores breaks the surface, causing it to become friable. The hygroscopic nature of the concentration of salts can also continue to draw moisture from the air, depending on the humidity within the building. due to this phenomenon the evaporation zone may appear damp and slimy to the touch even if damp is no longer rising damp.

The soil beneath the building must also be damp for at least part of the year if rising damp is to occur. Such ground conditions can be due to prevailing hydrology, such as marshy ground. However, in most cases involving historic buildings it is likely that the presence of moisture will be due to building failures or later interventions. Such factors may include raised external ground level or the failure of external drainage. Later interventions can generally be addressed and moisture ingress reduced to an acceptable level without installing a remedial damp-proof course and causing the associated damage.

It should be possible to approach all damp problems, including rising damp, through the following sequence:

1. assess visual evidence of dampness affecting the external and internal fabric of the building.
2. assess possible sources of moisture ingress associated with the pattern of visual evidence.
3. Carry out an accurate test of moisture levels within the affected areas to establish whether the dampness is current or past. Additional tests for soluble salts may be required in cases where rising damp is thought to be an issue.
4. Implement repairs or other appropriate interventions to control moisture ingress.
5. Implement appropriate measures to dry the building fabric, and monitor the drying process.
6. Carry out reinstatement works or cosmetic repairs. Most remedial firms will carry out a free survey of the problem and issue a report. Such reports can range from a fairly detailed assessment of the problem to, more often, little more than a quote for the work. Remedial firms and building surveyors will generally cover steps 1 and 2 to varying levels of thoroughness in order to make their assessment. Few will include step 3, other than to take a few measurements using an electrical resistance meter.

It is generally accepted that electrical resistance meters (also called moisture meters) are accurate when testing timber. But, despite reassurances from manufacturers, there is some debate as to their accuracy in masonry. Readings can be corrupted by the presence of salts within the masonry and may falsely suggest the masonry is damp. Most such meters are designed to measure surface moisture. Some are also designed to measure moisture at depth within masonry, using radio frequency. It is also possible to extrapolate a moisture reading from a measurement of relative humidity by inserting a thermal hygrometer into a predrilled hole in the masonry. Such methods may provide an indicative moisture reading but they cannot diagnose rising damp.

The moisture content of masonry can be tested accurately by removing a masonry sample for analysis. Samples are generally removed by drilling into the masonry from inside the building (the diameter would not generally exceed 15mm) and collecting the emerging dust. This can be tested on site using the ‘speedy carbide’ method or off site in a laboratory using the ‘oven-balance’ method. The speedy carbide method involves mixing a measured dust sample with calcium carbide in a sealed flask. The reaction produces acetylene gas. The more moisture is in the sample, the more gas is produced. Levels are measured by a pressure gauge on the flask. This method is useful for instant on-site moisture testing, but the results can not be analysed later to indicate the source of the moisture.

The most accurate test for moisture content in masonry and the presence of rising damp is the laboratory oven-balance method, as described by Building Research Establishment Digest 245. The process relies on a series of samples taken in a sequence up the wall at several positions around the building. The dust samples are sealed into vials and delivered to a laboratory. Moisture loss is calculated by accurately weighing and drying the samples. The level of hygroscopic nitrates and chlorides present can be calculated by submitting the samples to a relative humidity of 75 per cent. an accurate pattern of moisture and hygroscopic salt distribution can be plotted to show the distribution of damp within the walls and the presence of any rising damp.

Both the sampling methods above are to some extent destructive and there may be situations where such tests would be inappropriate. However, the damage caused by the sample extraction would rarely outweigh the potential damage caused by inappropriate remedial treatment.

Some remedial firms may use a carbide meter on request. Some will also use test strips to establish the presence of different salts. Such tests may add weight to a contractor’s diagnosis, especially if there is no visible evidence of later interventions leading to moisture ingress. Other than paid independent damp consultants, very few specialists would entertain the use of the oven-balance method as described in BRE digest, due to the time and costs involved.

The solution to a damp problem will depend on the correct diagnosis of the source of the moisture. If any evidence of dampness is observed at low level within a building, it is likely that in most cases contractors will specify the installation of an injected damp-proof course, especially where no damp-course is visible.

Installing a remedial damp-proof course will generally involve drilling and injecting a chemical preparation along the external base of the affected wall. The chemical is designed to spread out within the masonry, inhibiting moisture from rising. This process does not entirely eliminate rising moisture, so the internal plasterwork is generally replaced up to one metre around each room. a fairly impermeable render is used, providing a dry finish for re-plastering or decoration. This procedure will also conveniently mask any failure of the injected damp proof course.

It is also likely that the installation of a damp-proof membrane (dpm) across the floor may be specified. This would inevitably involve excavating the floor surface and installing a dpm usually in the form of a plastic sheet. a new floor surface would then be formed over the membrane.

Notwithstanding damage which may be present due to genuine damp problems, the damage and loss of original fabric caused by these procedures can be significant, such as the drilling of external holes, loss of original plaster, and excavation of floor coverings. The work may also destroy archaeological features such as wall paintings and earlier floor coverings. as moisture will take the line of least resistance, the introduction of impervious materials can push the problem to another part of the building if the cause of the problem is not properly addressed. There are unlikely to be many occasions where a remedial damp proof course would be considered by conservation professionals to be appropriate in a historic building.

In the past, mortgage lenders often insisted on a damp-proof course (with a guarantee) being installed if an existing damp course had not been identified in the building survey. However, the relative cost of most remedial work is increasingly insignificant in relation to the equity in the property, and most mortgage lenders do not now insist on such work. The absence of a paper guarantee may put off buyers in some cases.

Various electrical remedial damp systems, using a process called electro-osmosis to remove the moisture, have been marketed over the years. Such systems tend to be less invasive, the minimum requirement being the installation of an electrical control unit. Electro-osmotic systems require the installation of a conducting electrode in the form of a wire circuit buried within the base of the wall and running around the perimeter of the building. Most practitioners are highly sceptical about the performance of such technology. although firms are constantly marketing new forms of electrical remedial damp systems, they are not generally considered to be fully proven.

Atmospheric siphons have been in and out of favour for many years now. Most popularly marketed as ‘dalton tubes’, the technology is currently being marketed as a Dutch solution to rising damp. The procedure involves inserting a series of vents around the base of external walls to encourage moisture to evaporate from within the wall before rising further. The vents themselves tend to form the basis of the marketed product. They can take various forms, from cast-iron triangular tubes to circular ceramic designs. The ends of the tubes remain visible around the base of the external walls, causing visual detriment, and installing them causes physical damage. apart from the associated damage, the scientific theory behind the technology has apparently been discredited, not least by Giovanni and Ippolito Massari in the ICCROM publication Damp Buildings: old and new. Such solutions are not considered appropriate for use in historic buildings.

Later interventions affecting the performance of historic buildings are commonly responsible for damp problems around the base of buildings. Where possible these should be tackled before further remedial work is considered. damp masonry could take many months to dry following the elimination of the source of moisture.

Common later interventions include:
• external ground level raised above internal floor level
• raised flowerbeds built against external walls
• undrained hard surfaces built up against the base of walls
• trees and shrubs growing against buildings, encouraging moisture to dwell against the wall of the building and damaging subterranean drainage systems
• inappropriately designed rainwater drainage systems, such as down pipes that discharge at the base of the building
• inappropriate cementitious render or pointing encouraging a build-up of moisture within the fabric by directing rainwater into the building or discouraging evaporation.

The concept of the French drain is to intercept and reduce moisture around the base of external walls. The installation of a French drain involves excavation of a trench (commonly 600mm deep x 400mm wide) around the perimeter of the building to take a continuous, perforated land drainage pipe. The trench is normally positioned against the building or in a convenient position close to the perimeter. It is backfilled with a suitable gravel to allow free drainage and encourage evaporation of moisture from the trench or the base of the wall.

Conservation professionals generally favour French drains as a method of tackling damp at the base of historic buildings due to the minimal impact on the building’s fabric. However, there may be important archaeological and structural considerations to be considered in a particular case. Ian Hulme’s guidance note (an IHBC technical sub-committee paper) on French drains is available through the IHBC website.

Conservation professionals, faced with a scenario where rising damp has been offered as a cause but suspicious of or disagreeing with a proposed remedial solution, may want to investigate and negotiate. But they will remember that any standard remedial works can be highly destructive, can simply mask the problem and ultimately fail to address the cause of the moisture ingress.

If the building were listed, most standard remedial solutions would require listed building consent. In such cases an assessment by an independent consultant can be stipulated. Such an assessment would ideally involve tests using BRE digest 245. However, sourcing an independent assessment may not be straightforward.

The cost of an assessment by an independent damp consultant is often prohibitive for average-sized domestic properties due to travel and laboratory expenses. The choice of independent consultants offering specialist damp analysis for historic buildings is also extremely limited and the quality of service can be variable.

If you feel confident enough, it may be worth attempting a visual assessment of the situation yourself in the hope that there may be clear evidence of later interventions relating to areas of damp damage internally. Clearly, you may not be in a position where your professional indemnity enables you to dispute the judgement of another professional. Nevertheless, you may be able to persuade the client or building owner that it may be prudent to address the more obvious causes of moisture ingress before embarking on more damaging, and potentially more costly, procedures.

It is more than likely that the source of moisture affecting the base of the walls will be due to later interventions. Even if this is not the case and the presence of rising damp is proven, the use of a French drain represents a possible alternative solution.

The latest wonder damp-proofing product from Europe involving a magic box being fitted to a wall has arrived in the UK but instead of Germany this time it is coming from France and the explanation of how rising damp occurs in walls is as follows which was taken directly from the Mur-tronic website

WHAT IS RISING DAMP?

Because of its physical and geological characteristics, the Earth, which rotates and is covered by north-south magnetic “force-lines”, generates a considerable amount of radiation. This radiation includes the presence of electromagnetic fields that give rise to electrical charges in water molecules and in the capillaries of the materials used to build walls.

The charges are very weak, but combined with the electric charges resulting from the circulation of water in the capillary system (zeta potential), over a period of time cause rising damp in walls. The result is more or less evident depending on the type of material, its porosity, mineral salt content, etc. To understand what happens in the capillary system of materials, which comprises bipolar molecules of water, and capillaries, you need to know that the system behaves like a cylindrical electrical condenser. Different concentrations of charges are observed depending on the level of the layers of water molecules and capillaries. These charges from the electromagnetic fields attract water to the drier capillaries at a higher level, until a balance is reached and a tide-mark of dampness forms.

The solution to rising damp is the installation of one their Mur-Tronic units which neutralises the effect of the natural electromagnetic fields by creating a natural counter-field with an opposite phase, which cancels out the cause of rising damp .It consists of sending very weak electromagnetic signals to the capillary system, thereby constantly modifying the polarity of the layers separating the charges in the capillaries. The surface tension of water and the angle of the meniscus in the capillaries is changed.

This principle makes it possible to neutralise the links between the H2O and salt ions and to lower the surface tension of the water which is high because of hydrogen bridges. This result is achieved using very little energy, contrary to the principle of electro-osmosis, which requires a greater input of energy.

The movement of water towards the top of the wall is halted i.e. the osmotic pressure is thus destroyed and the walls dry out, even in very damp environments. It is easy to see that the process does not merely mask the effects of the rising damp, as is often the case with the chemical and other methods used over the past decades, but deals with the cause, i.e. the electrical characteristics of the soil and the chemical components of the walls.

SIMPLE AS THAT!

The sole UK distributor and installer of this unique but yet unproven damp-proofing system is Advanced Geo Humidity Solutions from Sidcup, Kent who offer a 10 year guarantee against the recurrence of rising damp but are only able to offer their free damp diagnosis service within a five mile radius of Sidcup.

The Mur-Tronic form of damp-proofing appears to be very similar to the system offered by a German company called Drymat who say their magic box system will strengthen the reverse polarity of the flow direction thanks to the additional wall electrodes and a soil earth electrode. Water and salts contained therein migrate in this manner perceptibly faster and more effectively.

We have not come across either of these forms of damp-proofing and would like to hear from any householder who has had either the Mur-Tronic or Drymat damp-control systems fitted and whether they have been effective or not.

These systems are much derided as having no effect on rising damp but they could have some slight benefit in removing dampness from walls as long as they get enough air flowing through the tubes or air chambers fitted in the walls. However their actual effect is limited by the strength and direction of the wind and will only work satisfactorily if the wind is blowing strong enough and in the right direction for sustained periods.

There only seem to be a few companies offering this sort of damp-proofing system. One of the main systems is widely promoted by Schrijver who often take out full page adverts in papers such as The Independent. Their claim is that the Schrijver System is a green alternative to chemical damp-proofing and that there will be no need for any internal plastering works.

There is still a lot of debate about the effectiveness of chemical damp-proofing but there is no evidence to indicate that either the Schrijver System or a similar system sold as the Holland Damp Proof System are the complete answer. There is not very much technical information about how the systems work on either Schrijver System or Holland Dampproofing websites but these systems do not have any third party accreditation or certification from the British Board of Agrément to confirm that these systems are effective as the claims made.

The only research undertaken about the effectiveness of the Schrijver System/Holland Damp Proof System was carried out a few years ago by the Independent Dutch Laboratory, TNO (Organisation for Applied Scientific Research) which states that the performance of these damp-proofing systems is governed by external environmental factors such as wind speed, wind direction, temperature and relative humidity.What it is really saying is that for these systems to work effectively then the wind has to be blowing in the right direction at a fairly high speed to have much effect on removing dampness from walls. These conditions are unlikely to occur for any extended time and the performance is further hindered by the fact that wind speed drops at ground level and therefore quite strong gusts of wind would be required for the units to perform effectively. .

In the UK wind usually comes in one direction at a time ( it might be different in Holland) and therefore if all the external walls of a detached house had Schrijver System/Holland Damp Proof System installed then it is likely that only one elevation wall would be subject to wind at any given time meaning that the units in the wind free walls will unlikely to be as effective as claimed by Schrijver or Holland DampProofing. .

Schrijver System/Holland Damp Proof System both claim that internal re-plastering will not be necessary and this is true if there is no rising damp present but then damp-proofing treatment would not be required anyway. However if there is rising dampness from the ground it the wall then the water travelling up the wall naturally by capillary action will have drawn soluble salts such as nitrates, chlorides and sulphates from the ground. These salts will contaminate wall plaster as the moisture migrates through the plaster as part of normal evaporation internally and as the salts are hygroscopic they will continue to attract moisture into the plaster and the wall will appear wet even though it may be dry behind the plaster. This is a similar process to what happens to normal household salt if a salt cellar is left in a humid kitchen then the salt will soon become soaked, lumpy and useless.

The only way of preventing any future dampness due to salt contamination is to remove the affected plaster and replace it with a render containing a salt inhibitor to prevent salts from passing from the wall into the plaster which would then be deposited on the wall surface. A better plastering system would be to incorporate some form of thermal insulation by applying a combined damp-proofing/insulating plaster such as Walltransform or dry-lining the walls with a water-proof membrane such as Platon and then overboarding this with a thermal plasterboard. Both of these plastering systems will prevent the passage of moisture and salts onto any internal wall finish and also lower u-values to around 0.3 and reduce heat loss and ultimately pay for themselves in the former of lower energy bills.

The YouTube video of installation of the Schrijver System shows the damp-proofing units being installed at a height of approximately 350mm which is much higher than that recommended for the installation of any retro-fit damp-proof course and if there is dampness in the ground it will rise to the height of the units before evaporating externally via the units. This will still cause some dampness in the plaster and skirting boards at ground level and these may need to be replaced in the normal way associated with damp-proofing works. .

Most rising damp occurs as a result of water from saturated ground passing into the below ground masonry walls which then become saturated themselves and as the walls usually have finer pores than the ground water will rise up the wall due to capillary forces. If there is no damp-proof course or a defective one then dampness can rise up to a height of more than 1.2m but the height of the dampness is controlled by a balance between evaporation from the wall and upward capillary forces. .

The most effective way of controlling rising damp is to remove the moisture source to prevent the base of the wall become wet and this can be achieved either by installing a French Drain or excavating the ground to create a vented channel covered with paving slabs/York stone or similar allowing moisture to evaporate from the base of the wall before it can affect skirtings and plaster at ground level. To further improve this method extra air bricks should be installed to ventilate sub-floor areas as the extra air flow under the floor will purge excess water vapour from the floor void, reducing humidity levels in the floor void and the possibility of condensation occurring on exposed masonry leading to ‘rising damp’ internally. Another benefit of improving the sub-floor ventilation is that the moisture content of sub-floor timbers such as joists and wall-plates etc would also be reduced and this would and lessen the risk of fungal decay or woodworm infestation making chemical timber treatments hard to justify.

We believe this form of damp control is much more effective than both the Schrijver System/Holland Damp Proof System and also any conventional retro-fit damp-proofing. If you need any further advice on which form of damp-proofing system is best for your house then please call us on 0800 028 1903 or email enquiries@ukdamp.co.uk

Clare McVey investigates damp diagnoses that leave consumers paying for unnecessary work

After viewing more than 20 properties, Denise Dawes felt she had finally found her dream Cotswolds cottage — until she was told she would need to spend more than £7,000 to fix a damp patch.

Dawes, 51, was buying a £120,000 Victorian cottage that had been completely renovated by the previous owners, so she had not been expecting large-scale works.

“The mortgage company asked me to get a damp survey done by a member of the British Wood Preserving and Damp-Proofing Association (BWPDA),” she says. “This chap showed me all the red lights flashing on his damp meter. I was horrified as we really wanted this cottage, so I decided to seek a second opinion.”

The vendors had had damp-proofing done, and a different surveyor confirmed that channels were already in place and that moisture being detected was caused by condensation and the recent plaster drying out.

Dawes’s house purchase is going through, but thousands of buyers each year are not so lucky. Damp — and the fear of it — plagues the housing market. Vendors are persuaded to drop their price, buyers back out, and homeowners fork out for expensive works. Despite the prevalence of the problem, however, consumers are still being ripped off.

Damp undeniably causes real damage. Chris Mahony, of the Royal Institution of Chartered Surveyors (RICS), says: “Damp can lead to rot in timbers, corrosion of metal fixings and mould growth. What is important is for the surveyor to correctly identify the cause. Rising dampness occurs much less frequently than one might think.”

Other common causes include condensation, plumbing leaks, the localised failure of the damp-proof course and water penetration caused by blocked gutters.

“Small localised areas are unlikely to affect the integrity of the building, but if dampness has started to cause timbers to rot, prompt remedial action will be needed,” says Mahony.

Even a full structural survey has its limits, however; Mahony warns that patches of damp may be lurking behind furniture or covered by paint.

So how do you know if you have a genuine damp problem? Surveyors often advise buyers to get specialist companies in to conduct damp surveys, but many firms offer “free” surveys and then recoup the cost by recommending extensive works.

Trevor Kent, a former president of the National Association of Estate Agents, says: “Surveyors are reducing their exposure by saying that houses must be checked by independent so-called specialists to absolve themselves of responsibility. But the surveyors are the trained experts. The woodworm and damp people often have no training at all.”

Kent cites one client advised by his surveyor to get a specialist damp report. The buyer asked three firms for their opinion; each one found damp in a different wall.

Another common problem is that guarantees offered for damp work “are not worth the paper they’re written on”, says Anthony Kerrigan, of Kerrigan’s Property Services in Doncaster. “I don’t think we have ever had a situation where a surveyor has found damp and we’ve been able to claim on a guarantee. They’ve either gone out of business or claim the problems are related to an area they didn’t treat.”

Although guarantees offered by members of the BWPDA, the leading trade body, are backed by insurance if the company goes out of business, only 10% of firms operating in this area are members. In any case, even BWPDA companies may employ their surveyors on a commission basis, meaning that they have an incentive to “find” work.

Chris Coggins, director of the BWPDA, says the body encourages members to charge for their professional services. “The so-called free survey was introduced as a marketing ploy and has not served the industry or the public well.

“We would take disciplinary action against a member found to be fraudulently recommending work, knowing it was unnecessary.” But, he says, “there may be more than one way to deal with the problem”.

Paul Taylor of UK Damp & Decay Control spent years installing chemical damp-proof courses before realising, he says, that he could offer customers simpler and more cost-effective solutions.

“Much of this work is unnecessary as rising damp is often assumed to be the problem, when it may instead be condensation or penetrating damp, which can usually be remedied at a fraction of the cost of chemical works.”

Steve Playle, a Surrey trading standards officer, advises: “Don’t assume the companies with the biggest ads are necessarily the best. The bigger companies tend to subcontract which means they have less control over the work. If you think you’ve been ripped off, notify trading standards. If we have a few complaints about the same company we will investigate.”

The Rated Column in the News of The World focuses on damp and has lots of good advice about how to prevent dampness in the house.

It also has a small sub-column headed Cancer of Buildings relating to Dry Rot stating that the fungus can spread through a house in a manner similar to cancer and that the only course of treatment is to spray houses with chemicals and remove affected sections of wood and stone.

Most of these chemical treatments are not really required as dry rot can be controlled by removing the source of moisture and as dry rot is essentially a plant it will die out naturally without the need for mass use of fungicides to irrigate walls.

Other chemical free forms of dry rot eradication involve heat treatment of whole or part of buildings which successfully kills any fungus and beetle infestation or sacrificing the blood of two doves on affected sections of houses to kill fretting leprosy of the house as described in The Old Testament (Leviticus Chapter 14 verses 33-53).

But really common sense is all that is required in the treatment of any dry rot. Cut off the source of moisture, cut out any decayed timber and affected sections of plaster, promote rapid drying and then re-instate timber and plaster. No chemical treatments required.

Often dry rot stems from penetrating dampness due to a gutter or plumbing leaks but the most common cause that we find when carrying out damp surveys is where the original damp-proof course has been bridged and air bricks providing sub-floor ventilation have been blocked.

We have currently been on one such project in Tudor Hill, Sutton Coldfield, Birmingham B73. These are well built houses and normally would not have a problem with dampness or dry rot but the damp course had been bridged by a blocking paving drive and this had partially covered the air bricks and water flowing down the slope of the drive was being diverted into the sub-floor area through the air bricks. This resulted in a build up of moisture under the floor which lead to dampness and then dry rot in the floor timbers. We had to remove the entire lounge floor and replace it with new timbers after we had sterilised the affected area with a combination of heat treatment and organic preservatives. The work cost over 10,000 pounds but this could have been avoided if the contractors who installed the paving had created a drainage channel at the base of the wall and not blocked off the air bricks.

While on the job I took my dogs for a walk in Sutton Park and then a bit of phsychogeography around the local area including Driffold, Wylde Green,Maney etc. Most of the houses in the area are semi-detached or detached properties built around 1930-40 and all have a combination of a physical damp-proof course and a band of blue engineering bricks at the base of external walls to prevent rising dampness. However roughly twenty percent of the houses had their damp-course bridged and air bricks blocked by block paving drives so I expect thet we will be getting a few more calls in this area of Birmingham in the next couple of years as the damp and rot sets into these houses.

For more advice on the correct diagnosis and treatment of dry rot then please call us on 0800 028 1903 or e-mail enquiries at ukdamp.co.uk (anti-spam so please replace at with @ )