Dry Rot and Timber Decay: Don’t Panic and Poison Yourself

Jagjit Singh PhD is a building mycologist and pathologist and a director of Environmental Building Solutions Ltd (EBS). He specialises in building health problems, heritage conservation and environmental issues and has more than 33 years’ hands-on experience in surveying historic buildings. 

Read the full article here;

Dry Rot and Timber Decay: Don’t Panic and Poison Yourself - Received (in revised form): 8th January 2020 

Jagjit has carried out environmental surveys for dry rot, wet rot, moisture, damp and decay, moulds, environmental health surveys and monitoring historic buildings, and provided recommendations for environmental control. 

EBS’s reputation in non-intrusive investigations for dry rot, wet rot, timber decay, damp, hazardous materials surveys, heritage building investigations and the development of innovative techniques - including recommendations for environmental management sympathetic to the building fabric finishes and components and the non-use of chemicals and cementitious tanking materials — is well respected by conservation and heritage authorities. 

Jagjit has published in excess of 250 technical papers and communications, contributed to books and lectured widely on care and conservation of col- lections, building pathology and building health problems, covering wide areas including fungal infestation and environmental control, timber decay in buildings, damp and decay in buildings and drying out buildings after fire and water damage, environmental monitoring and control of moisture, mould and biological contaminants, Indoor air quality and health implications in buildings. Jagjit has edited several books including Building Mycology: Management of Decay and Health in Buildings, Environmental Preservation of Timber in Buildings, Allergy Problems in 

Buildings and Environmental Monitoring of our Cultural Heritage and Sustainable Conservation Solutions. Jagjit is a BBC expert and has appeared twice in the Raising the Roof series. He is a former president of the International Society for the Built Environment (ISBE). 

Abstract

This paper first shows that timber decay in buildings is primarily due to lack of maintenance and building defects, allowing water penetration into the building fabric providing ideal environ- mental conditions for fungal and beetle infestation. Secondly, the paper sets out how it is very important that investigations are non-destructive and result in the correct diagnosis and identification of type and viability of decay. Thirdly the paper discusses the author’s belief that the remedial chemical timber treatments stem from fear and a lack of knowledge of dry rot, and that the demand for 30 year guarantees for treatment results in ‘over- kill’. 

The paper advocates that the environmental control of dry rot and timber decay and preventative maintenance are preferable to conventional remedial treatments. This approach is based on scientific, practical experience and successful case studies carried out over the last 33 years, and provides not only environmentally sustainable holistic conservation solutions, but also ensures the long-term health of building materials, health of the occupants and structures.1

Keywords: timber decay survey, dry rot identification, environmental control of dry rot, non-destructive inspection 

Jagjit Singh 

Environmental Building Solutions Ltd, Passenham Manor, Passenham, Milton Keynes MK19 6DH, UK 

Journal of Building Survey, Appraisal & Valuation
Vol. 9, No. 1, 2020, pp. 49–64 © Henry Stewart Publications, 2046–9594 

SUMMARY 

Dry rot, wet rot and timber decay in buildings is mainly attributed to environmental conditions favouring fungal infestation and decay. A range of factors can contribute to moisture ingress into the fabric of the building, including penetrating damp/rising damp, condensation, fire/flood disaster, construction moisture, building defects and lack of ventilation. 

The damage caused by dry rot and decay organisms is very familiar, as is the destruction arising from attempts to: 

• Locate the extent of dry rot and wet rot infestation by unnecessary extensive exposure works to buildings; 
• Cut out large-scale healthy timbers for the fear of dry rot and wet rot infestation; 
• Remove large-scale healthy timbers for fear of re-infestation; 
• Eradicate dry rot and wet rot infestation by the use of injected chemicals, which not only are a cause for concern to the building owners and occupiers, health authorities, wildlife interests and environmentalists, but also lead to the development of resistance in the target organisms. 

The internal environment of a building, predisposing it to the development of infestation and decay, is the product of a number of influences and interactions. Before under- taking a remedial intervention involving any building, it is advisable to study in detail the ecological factors such as moisture and humidity at micro-environmental levels, including the building’s response and performance. 

Misidentification leads to misdiagnosis and mistreatment. Therefore, in the author’s view, correct identification of the fungal infestation is important, as not all fungi are equally destructive and fungal infestation may even be dead, representing conditions in the past. 

Remedial measures could entail the loss of decorative finishes, extensive exposures and damage to the fabric of the building, which is very expensive. It is not surprising therefore that the estimated annual expenditure on timber preservation works in Britain is over £400m.2 

Based on scientific and practical experience and successful case studies over the last 33 years, the author has advocated that environmental control and preventative maintenance are preferable to remedial chemical means. Preventative maintenance should in most cases forestall the need for major interventions and it is beyond doubt that it reduces the cost of the conservation of buildings. 

This environmentally sustainable holistic approach and the ongoing monitoring of the environmental conditions in buildings ensure the long-term health of building materials and structures.3 

BUILDING APPRAISAL FOR FUNGAL INFESTATION AND DECAY

It is estimated that there are approximately 1.5m species of fungi in total, of which around 70,000 (5 per cent) have been scientifically described. ‘Building mycology’ is defined as that branch of mycology dealing with the study of fungi in and around the building environment.4,5 This has both direct and indirect effects on the health of building materials, structures and occupants. 

The most common fungi to cause damage to building structures are the following:

Dry rot fungus
• Serpula lacrymans 

Wet rot fungi
• Cellar rot fungus (Coniophora puteana)
• Antrodia vaillantii, Antrodia xantha and A. sinuosa
• Asterostroma species 

• Donkioporia expansa 
• Paxillus panuoides 
• Phellinus contiguus 
• Pleurotus ostreatus 
• Tyromyces placentus 

A full description of all the types of fungal decay, and indeed fungi, found in the built environment is beyond the scope of this paper and the reader is referred to the Indoor Built Environment paper6 for further information. 

Dry rot 

This fungus has occupied a specialised ecological niche in buildings in Europe with its unique biology and is only known to occur in the wild in the Himalayas (see Figure 1). 7–14 

It first became recognised as being of economic significance in the UK in the 17th century when ships of the Royal Navy were decomposing faster than they could be built, culminating in the case of the Queen Charlotte, launched in 1810, which cost far more to repair in 1812 than to build two years before. 

The damage to the ship was almost certainly caused by dry rot fungus S. lacrymans. The causative organism of these early attacks is sometimes recorded as Boletus lacrymans, although by the 18th century the organism had been more formally named as Serpula lacrymans by von Wulfen (1781). In 1912 S. lacrymans was renamed Merulius lacry- mans (Falck 1912). In recent decades a return to von Wulfen’s nomenclature has occurred.15 

The vast majority of properties in the UK contain a significant amount of wood, ranging from structural timbers such as joists, trusses and rafters to finishings such as skirtings. Therefore, the dry rot fungus S. lacrymans (Schumach. ex Fr.) is the most important timber decay fungus in buildings in northern and central Europe and is also of serious concern in Japan and Australia.16 Not only does the fungus bring about the dramatic decay of timber, but it is also able to spread through a building from one timber location to another across non-nutritional surfaces. 

The fungus has a serious impact on the UK housing stock and also causes concern in the conservation and preservation of buildings of historic and architectural merit.17   The destruction caused by dry rot is worse if left unnoticed, and sometimes the final signs of decay are the appearance of fruiting bodies in various parts of the building. At this stage major damage to structural timbers has already occurred. 

Figure 1: Wild dry rot discovered in the Himalayas                                                                                                            Figure 2: Dry rot fruiting body 

The ravages of the dry rot fungus are familiar, as is the destruction caused by attempts to eradicate it, particularly involving the use of chemicals. Remedial chemical timber treatments can cause damage to the health of building occupants and are a cause for concern to environmental health authorities. 

Building surveyors in particular have to look out for dry rot and wet rot fungi when they are appraising properties. They have to consider the factors that may indicate the likely cause of internal decay whether past, present or future.18,19 The technical and legal implications associated with S. lacrymans should not be underestimated. Building surveyors must alert their clients to the risk of timber decay when carrying out either a structural/building survey or a house buyer’s report and valuation. 

Correct and early diagnosis of this form of infection in a building is essential if a later widespread outbreak is to be avoided and proper repair is to be achieved. It also mini- mises the chance of carrying out inadequate or excessive treatment where S. lacrymans is mistaken for wet rot or vice versa.20 In addition, early correct diagnosis will help the surveyor avoid a negligence claim in the event of a future outbreak of the rot. Not only is fungal infection of timber unsightly and potentially hazardous to human health, it can also adversely affect the structural integrity of the timbers as well as disrupt the use of the building.21,22 

Dry rot in its early stages is difficult to distinguish from other wood rots without the benefit of laboratory analysis. This involves growing samples of the fungus on an artificial medium under controlled conditions. Various media based on oatmeal, wheat flour and malt extract can be used as a nutrient to encourage fruiting of the fungus. 

It is the lack of understanding of the biology and ecology of the dry rot fungus that has led to this radical treatment and hence considerable damage to building fabric. The author has led several expeditions to search for wild dry rot in the Himalayas with a view to gathering information on its biology, ecology and genetics in the wild. 

It is hoped that the fundamental scientific knowledge gained through multidisciplinary research should enable us to reach a better understanding of the fungus and to develop safer, more effective and ecological control 

techniques and strategies.23,24,25,26,27,28,29,30,31,32 

TIMBER CONDITION SURVEYS 

The majority of the timbers described below are vulnerable to decay and should be investigated: 

Timbers vulnerable to dry rot, wet rot and timber decay 

DAMP AND RESIDUAL MOISTURE SURVEYS

Alongside timber condition surveys, it is of paramount importance to carry out damp, residual moisture and moisture distribution surveys to understand the moisture sources, moisture reservoirs and moisture sinks. This will enable a strategy for environmental control of infestation and decay. 

Techniques to evaluate distribution of moisture in the fabric of the building should be investigated and should include: 

• Moisture mapping; 
• Mortar sampling; 
• Render analysis if required; 
• Residual moisture, salts and total moisture; 
• Surface and deep moisture content in timbers.  

Environmental factors affecting timber decay
The environmental factors affecting the decay of timber are temperature, water, humidity and ventilation.33 

Moisture in buildings 

The following factors contribute to moisture in buildings: 

• Penetrating damp/rising damp; 
• Condensation; 
• Building disaster; 
• Construction moisture; 
• Building defect. 

Temperature 

Fungi differ in their optimum temperature requirements but for most the range is from about 20°C to 30°C. The optimum temperature for dry rot growth in buildings is about 23°C, maximum temperatures are approximately 25°C and the fungus is rapidly killed above 40°C. Timber moisture content in buildings in the 20–30 per cent range are ideal for dry rot attack and other infestations. 

BUILDING SURVEY MAIN OBJECTIVES - Building type, age, construction and maintenance

Establish the client’s instructions and the purpose of the investigation. Ascertain the property’s age, form of construction and orientation. A knowledge of its location and recent history, especially as regards the level of maintenance and occurrence of adapta- tions (if any), may also be revealing.

Moisture zones: Identify actual or potential sources of dampness;34
Timbers appraisal: Forecast the probable presence of hidden timbers within the building; Dampness defects: Identify and diagnose defects that can cause dampness; 

Risk factors: Pinpoint vulnerable areas such as floor/roof/wall voids, look for external and internal indicators such as dampness; if there has been a previous infection, there is a higher risk of a further outbreak;

Reporting: Accurately and impartially report the nature and extent of decay. 

BUILDING SURVEY AND INSPECTION METHODOLOGY

A careful, systematic methodology is required when carrying out a building survey. One of the objectives is to assess the likely location or danger of dry rot. Unless the property is new or relatively modern, it may be safe to start with the assumption that dry rot is probably present until proven otherwise. The aim in any inspection of a building for dry rot is to identify infected or vulnerable areas and to provide a logical assessment of the risks. This is usually best achieved if the same methodical approach used for a typical building survey is adopted, as summarised. 

Primary inspection 

Externally: Top down — look for typical indicators of rot; algae growth on walls, damp stains on walls, choked/overflowing gutters, defective roof coverings, leaking/ faulty rainwater downpipes, defective pointing/rendering. 

Internally: Top down — all visible timbers should be inspected; note symptoms such as warped or curled wall panelling boards, splitting and cracking of painted woodwork, strong mushroom smell in the vicinity of an outbreak, springing lintels or floors and, of course, fruiting bodies with a layer of red dust-like spores. 

Secondary inspection 

Once the ‘at risk’ areas have been identified, it is advisable for the surveyor to recommend further investigations which may involve an element of ‘opening-up’, uplifting floorboards, removing sections of timber panelling, etc. The use of a fibre- optic endoscope will help to minimise such work (see below). Solum levels of sub-floor voids that are below the outside ground level are potentially troublesome areas because they are prone to flooding and are difficult to ventilate adequately. If the finish of a sus- pended timber floor is at or near the outside ground level, then the latter will be above the solum level, and this should be checked.

Detailed investigation

The findings from the initial investigations may be followed up by more detailed study. The aim is to determine the distribution and extent of all significant decay organisms in the building, the distribution of all micro- environments predisposing to timber decay and the building defects that cause them.

The distribution of moisture and its movement through the structure is particularly important. The extent of significant timber decay should also be determined. Active decay organisms may not yet have caused significant timber decay.  Conversely, there may be significant decay even when the decay organisms that caused it have been dead for many years. Key factors to be noted are species and viability of decay organ- isms, moisture content of materials, ambient relative humidity and ventilation. Timber species and previous chemical treatments may also be significant.

It is important that the results of the investigation are coordinated with the building structure, bearing in mind the characteristics of particular periods and methods of building. They should also be carefully recorded and quantified where possible. This allows analysis of the results by other experts, reduces the ‘grey’ area in which differences of opinion can arise, and forms a basis on which future investigations can build. This recording of data is especially important in the current legal climate and photography can be especially valuable. A detailed investigation of this sort might take about five man-hours for a typical three-bedroomed house. 

Special search techniques 

The condition of concealed timbers and cavities may be deduced from the general condition and moisture content of the adjacent structure. Demolition or exposure work can enable the condition of timber to be determined with certainty, but this destroys what it is intended to preserve. A non- destructive approach is therefore required and, to help reduce uncertainty, instrumentation and test equipment can be useful at this stage. It is important to remember, however, that all tests and instruments are only aids to the surveyor and must be interpreted with experience and care. A slavish reliance on any technique, and failure to consider its limitations, is a recipe for disaster. Non-destructive techniques include fibre-optic inspection and ultrasonic and infra-red methods. 

Timber moisture content at the surface may be estimated using a resistance-type moisture meter, fitted with insulated needle probes. This will fluctuate depending on relative humidity and temperature. A rafter may have a surface moisture content of 16 per cent in summer that might rise to over 20 per cent in winter. This would not necessarily indicate increased water content from a fault in the roof but might be water absorbed in conditions of lower temperature and higher relative humidity. The core of the timber will remain relatively dry and a hammer probe with insulated electrodes is recommended for measuring the subsurface moisture content. 

Masonry moisture content

The estimation of surface moisture content in plaster and mortar is of limited value except for comparison. A surface capacitance meter may be used on plastered walls and panelling to detect areas requiring further investigation. Absolute readings should be made by means of a carbide-type pressure meter or by the oven drying method. Moisture reading contours on the surface and in the thickness of the wall help to define the source and type of moisture giving rise to decay. 

Main characteristics of decay of timber
There are four key characteristics that can be used in the identification of fungal infestation and decay in buildings: 

(1) Mycelium;
(2) Appearance of decayed wood;
(3) Strands (rhizomorphs);
(4) Appearance of fruiting bodies or sporophores. 

ASSOCIATED ROTS AND MOULDS 

Wet Rot

This type of decay is caused by a number of basidiomycetous fungi, of which the most important are Coniophora puteana (cerebella), ‘Poria’ fungi, Phellinus contiguus, Donkiporia expansa, Pleurotus ostreatus, Asterostroma spp and Paxillus panuoides. Wet rot is also called white rot as it destroys both cellu- lose and lignin, leaving the colour of the wood largely unaltered but producing a soft felty or spongy texture without cross cracks. Common white rots are Donkiporia expansa, Asterostroma spp, Pleurotus ostreatus and Phellinus contiguous.35 Brown rots cause the wood to become darker in colour and to crack along and across the grain; when dry, very decayed wood will crumble to dust. Many common wet rots are brown rots, for example Coniophora puteana, C. marmorata, Paxillus panuoides and Dacrymyces stillatus. Table 1 compares the characteristics of dry rot and wet rot.

DETECTION OF DRY ROT 

• An understanding of the physiology, morphology and pathology of the fungus; 

• A sound knowledge of building structure and construction; 

• A sound knowledge of environmental conditions; 

• A sound knowledge of moisture mapping in the building fabric; 

• A sound knowledge of wood science and pathology. 

Determining the presence of hidden or built-in timbers is crucial to a full and accurate detection of the fungus. There are several techniques that the surveyor can use to help in arriving at a correct diagnosis and these are listed in Table 2. 

Table 1: Main characteristics of fungal decay of timber 

Mycelium 

Dry Rot - Damp conditions: masses of tears on silky white surface, with bright lemon patches Drier conditions: thin skin of silver grey in colour, with deep lilac tinges 

Wet Rot - Only present in conditions of high humidity: cream to brownish in colour

Decaying Wood

Dry Rot - Deep cuboidal cracking associated with differential drying shrinkage Reduction in weight Dull brown in colour Resinous smell gone 

Wet Rot - Cuboidal cracking on smaller scale and less deep. Thin skin of sound wood. Weight loss. Localised infection 

Strands (rhizomorphs)

Dry Rot - 3–6mm in diameter Brittle when dry off-white/dark grey in colour 

Wet Rot - Thinner than dry rot Brown or black, yellowish when young 

Sporophores (fruiting)

Dry Rot - Tough, fleshy pancake or bracket-shaped, varying from a few cm to a metre across Ridged centre: yellow-ochre when young, darkening to rusty red when mature Lilac/white edged. Distinct mushroom smell. 

Wet Rot -  Not very common in buildings Thin, lying flat on the substrate, and with small irregular lumps. Olive green to olive brown with cream margin; paler when young. 

Table 2: Primary detection methods - Detection methods

Human senses

• Visual (Warping or cuboidal cracking in wood) 
• Aural (Hollow sound when tapping)
• Olfactory (Musty smell)
• Touch (Spongy, friable when felt or probed)
• Taste (Acrid)

Non-human senses 

• Sniffer Dogs - Specially trained dogs to locate dry rot outbreaks (limitations: cannot detect dead dry rot, any other form of wet rot decay, surface decay or pockets of old decay, which is equally significant) 

 Artificial detection 

• Moisture meter - Necessary to confirm damp areas
• Hand mirror & torch - To help inspect awkward voids
• Ultrasonic hammer - Can help to indicate the soundness of large joists
• Endoscopes - To inspect inaccessible areas
• Genetic - DNA analysis of rot samples 

Although dry rot primarily attacks soft- woods, it can also infect hardwoods such as oak.

In its terminal stages when the fruiting bodies or sporophores have developed brown spore dust, dry rot is relatively easy to distinguish from wet rot (see Figures 3, 4, 5, 6, 7 and 8). 

Other techniques include microscopy, laboratory culture and identification of fungi, hot wire anemometry and electronic relative humidity (RH) measurement (see Figure 9). Other techniques may sometimes be useful, such as infra-red thermography, short wave radar, automatic weather stations, ultrasonic detection and environmental monitoring using specialist data loggers for historic buildings of architectural and cultural merit.

Figure 3: Dry rot fruiting bodies Source: Author

Ecological factors influencing biodeterioration

When considering any form of biodeterioration, there are three factors of concern: the material, the environment and the organism. Ecology as an aspect of science is usually confined to a very close analysis of the inter- action of organisms with one another and with their environment. The environment in which any organism lives will contribute physical, chemical and biological factors that will have a bearing on the settlement, growth and development of an organism. 

Figure 4: Dry rot fruiting bodies                            Figure 5: Dry rot fruiting bodies                      Figure 6: Dry rot red dust from spores 

Assessment of decay in timber beams using a Resistograph decay detection drill

The structural integrity of the timbers in buildings, e.g. trusses, purlins, joists, wall plates, beams, etc. can be assessed with the use of a resistograph decay detection drill to establish the extent of decay and type of repairs required (see Figure 9).36 

Decay may not be immediately apparent because a surface layer of sound timber hides the decay within the beam; some- times the decay is in the middle of the beam, with a thin veneer of sound timber on the outer face. This is typical of dry rot, which is very sensitive to air movement and desiccation. It is trying to maintain the ideal environment to decay the timber away from sunlight and air movement leaving the surface veneer. 

The extent of the decay along the beam is governed by the amount of moisture available to the dry rot. The dry rot can generate moisture when digesting cellulose, which can maintain the decay in the absence of desiccating air movement. The decayed timber remaining is mainly lignin. 

The resistograph is a device based on the drill resistance measurement principle. The measurement accuracy can even detect the differences in the density of early and late sapwood. The drill canal is so fine that the drill shavings remain in the wood and almost no air can enter the wood, which minimises the decay infection. 

Examples of successful case studies include Hampton Court Palace, Tower of London, Pacific Wharf flats, Wandsworth tower blocks, Belgrave Square buildings, St James Square buildings, Norwich Union Headquarters building, Westminster Abbey, Passenham Manor, Eaton College, Harrow School, Deal Castle, Windsor Castle and Dover Castle. 

Determine the age of dry rot for legal and insurance claims

Based on a sound building mycological knowledge and expertise in timber pathology, it is possible to determine the age of decay in legal and insurance claims. 

This is based on the calculations of the extent of decay in timbers and extent of spread of the dry rot over time. 

Non-destructive inspections of hidden cavities and voids

Environmental Building Solutions has pioneered the use of an air sampler for carrying out non-destructive inspections of hidden cavities and voids in historic buildings. This machine extracts a known volume of air from a hidden void or cavity through existing holes in the fabric or through small holes made discreetly. The collected sample can then be analysed for, for instance, dry rot, wet rot and mould spores. Normal back- ground levels of spores would indicate a low risk of decay; high levels would indicate a problem in the void, which can then be followed up using fibre-optic inspection and Resistograph decay detection drills to investigate hidden timbers (see Figures 10 and 11).

Chemical control of biodeterioration 

A great variety of toxic chemicals is available on the market for use as wood preservatives. The ideal wood preservative should possess the following characteristics: 

• A high toxicity towards wood-destroying organisms; 
• Permanency in treated wood, that is, low volatility and a high resistance to leaching; 
• Ability to penetrate deeply into the wood; 
• Non-corrosive to metals and non-injurious to the wood itself; 
• Reasonably safe to handle and without injurious effects to operatives and occupants. 
• Wood preservatives are regulated in the UK under the Control of Pesticides Regulations 1986. 

 Figure 7: Dry rot red dust from spores                                                                                                             Figure 8: Dry rot mycelium 

REMEDIAL TREATMENT 

Remedial treatment is the conventional or traditional way of dealing with dry rot, wet rot, beetle infestation and timber decay as advocated by many of the timber treatment firms. The problem stems from their customers and the mortgage lenders requiring guarantees for treatment, which can end up with ‘overkill’, as described in this paper. 

Remedial treatment of dry rot 

• Establish the size and significance of the attack. Particularly if structural timbers are affected, carry out or arrange for a full structural survey to determine whether structural repairs are necessary and, if they are, take appropriate steps to secure structural integrity; 
• Locate and eliminate sources of moisture; 
• Promote rapid drying of the structure; 
• Remove all rotted wood cutting away approximately 300–450mm beyond the last indications of the fungus; 
• Prevent further spread of the fungus within brickwork and plaster by using preservatives; 
• Use preservative-treated replacement timbers; 
• Treat remaining sound timbers that are at risk with preservative (minimum two full brush coats); 
• Introduce support measures such as ventilation pathways between sound timber and wet brickwork, or, where ventilation is not possible, provide a barrier such as a damp-proof membrane or joist hangers between timber and wet brickwork; 
• Do not retain dry rot infected timber without seeking expert advice. There is always some risk in retaining infected wood, which can be minimised by preservative treatment and subsequent reinspection.

Environmental control of biodeterioration

When considering the prevention of any form of biodeterioration, there are three factors which can be considered: the material, the environment and the organism. 

The removal or alteration of any one of these can prevent the growth of decay organisms.37,38,39,40,41,42

The control of the environment of a susceptible material, instead of the application of biocides, is the oldest and still the most widely used method of preventing biological deterioration. Traditionally, the control of physical conditions has been by far the most important method of preventing biodeterioration. For example, in the use of timber in construction the object has been to prevent its moisture content rising to levels at which wood-rotting fungi can thrive. 

The basic principle in the control of fungal growth is to render the micro-environment in or around the material in buildings as hostile as possible to the settlement, germination and spread of micro-organisms. This can be achieved in various ways: 

1. To prevent or limit biological agents’ growth and proliferation by means of toxic chemicals; 
2. To ensure that the material to be protected is kept, or keeps itself, in such physical condition that growth of bio- logical agents is severely limited or prevented entirely. 

The second approach will be discussed in more detail as, traditionally, the control of physical conditions has been the most important method of preventing biodeterioration. The application of the general principles of the control of physical conditions and the reactions of micro-organisms to these conditions often results in the most effective and economical prevention of deterioration. 

Figure 9: Resistograph in use to check timber beam                           Figure 10: Air sampling of a historic void behind decorative finishes 

Figure 11: Fibre-optic (borescope) inspection of the void to investigate dry rot.  

The environmental (greener) approach

Environmental control relies on controlling 

• Locate and eliminate sources of moisture;
• Promote rapid drying; 
• Determine the full extent of the outbreak; 
• Remove the rotten wood;
• Determine structural strength of timber and fabric construction;
• Institute good building practice: 
• Ventilation;
• Damp proof membrane; 
• Isolation. 

 Environmental control is complex and requires a multidisciplinary team of scientists, engineers, surveyors and computing skills. 

Green approach standards 

In cases of actual or suspected problems of wood rot or wood-boring insects in buildings, the following standards should be met by any remedial works: 

(a) Investigation should be carried out by an independent specialist consultant, architect or surveyor to establish the cause and extent of the damp and timber decay, including the potential risk to the health of occupants, before specification or remedial work. This investigation should include: 

(i) The inspection of all accessible timbers to determine whether they are subject to, or at risk from, fungal decay or insect attack; 

(ii) The determination as to whether any wood-rotting fungi or wood- decaying insects found are active and whether their activity is significant in each case. 

(b) The specification of remedial work should be prepared by an independent consultant as in a) (i) and (ii). Such specification should provide for: 

•   The maximum conservation of materials; 
•   The future health of the building and its occupants; 
•   The minimal use of new materials; 
•   The avoidance of chemical pesticide use where possible;
•   The use of materials and techniques with minimum adverse environmental impact; 
•   The minimum cost of the whole project, including the costs of the proposed works, the disturbance of occupancy, future    maintenance costs, and  the cost of safe disposal of all waste materials. 

(c) Remedial building works should be carried out as specified above to control timber decay, to prevent further decay and to correct any significant building defects resulting in conditions of high moisture content or poor ventilation of timber. These should provide for: 

• The reduction of the sub-surface moisture content of all timber below 16–18 per cent; 
• The isolation of timber from contact with damp masonry by air space or damp-proof membrane; 
• The provision of free air movement around timber in walls, roofs and suspended floors; 
• Humidities in voids not exceeding an average relative humidity of 65 per cent; 
• The removal of active fungal material and any timber affected to the extent that its function is compromised, or adjacent structures put at risk, in the case of insect infestation, measures to avoid contamination; 
• The prevention of, or protection of timber from, sources of water likely to cause wetting such as over- flowing gutters, leaking plumbing, condensation and rising or penetrating damp; 
• The removal of all builders’ rubbish from voids and cavities and vacuum cleaning to remove dust. 

(d) The use of chemical pesticides is not necessary to control fungal decay in buildings. 

Environmental monitoring 

Environmental monitoring53,54 includes the data logging of temperature, humidity, moisture content and other parameters in building materials, including internal and external environmental conditions, using on-site sensors and an automatic weather station. Measuring the moisture content in timber and monitoring the drying of buildings provide simple and economical methods of avoiding serious timber decay. 

These systems accurately determine the source and distribution of moisture within the building fabric and detect water penetration in critical areas, or monitor drying following building failure, fire or flood.55,56 Data from these investigations is used to determine a policy and control the drying out of the building fabric to reduce the risk of future decay after refurbishment. 

References 

(1) Singh, J. (1999), ‘Dry Rot and Other Wood Destroying Fungi: Their Occurrence, Biology, Pathology and Control’, Review in Indoor Built Environment, Vol. 8, pp. 3–20, available
at https://www.ebssurvey.co.uk/docs/ Dry%20Rot%20and%20other%20 wood%20destroying%20fungi.pdf (accessed 23rd January 2020). 

(2) Douglas, J. and Singh, J (1995), ‘Investigating dry rot in buildings’, Building Research and Information, Vol. 23, No. 6, pp. 345–352. 

(3) Ibid., ref. 1.

(4) Singh, J. (1991), ‘New advances in 

identification of fungal damage in buildings’, The Mycologist, Vol. 5, No. 3, pp. 139–140. 

(5) Singh, J. (1994), Building Mycology, Management of Health and Decay in Buildings, E. & F. N. Spon, London. 

(6) Ibid., ref. 1.

(7) Bagchee, K. (1954), ‘Merulius lacrymans (Wulf) Fr. in India’, Sydowia, Vol. 8, pp. 80–85
(8) Singh, J., Bech-Andersen, J., Elborne, S. A., Singh, S., Walker, B. and Goldie, F. (1993), ‘The search for wild dry rot fungus (Serpula lacrymans) in the Himalayas’, The Mycologist, Vol. 7, No. 3, pp. 124–130. 

1. Singh, J. (November 1992), ‘On the trail of dry rots grandpa’, Daily Telegraph. 

10.  Singh, J. and White, N. (1995), ‘The search for a Himalayan link to a dry rot cure in   buildings’, Building Research and Information, Vol. 23, No. 4, pp. 216–220. 
11.  White, N., Singh, J., Singh, S., Walker, B. and Palfreyman, J. ( March1995), ‘Searching for answers at the roof of the world’, Buildings and Facilities Management for the Public Sector, pp. 14–16. 
12.  White, N. and Singh, J. (1995), ‘Himalayan origin of dry rot: Comparative ecology in domestic and wild environments’, Proceedings of Environmental Preservation of Timber in Buildings Conference, Dublin. 
13.  Palfreyman, J., White, N. and Singh, J. (1999), ‘Timber Preservation: The Potential Use of Natural Products and Processes’, in Singh, J. and Aneja, K. R. (eds), From Ethnomycology to Fungal Biotechnology, Plenum Publishing Company, New York. 
14.  For detailed information please refer to Singh, J., Bech-Andersen, J., Elborne,
    S. A., Singh, S., Walker, B. and Goldie, F. (May 2009), ‘The Search for Wild Dry Rot Fungus (Serpula Lacrymans) in the Himalayas’, available at https://www. ebssurvey.co.uk/docs/Search%20for%20 Dry%20Rot%20Fungus%20in%20the%20 Himalayas,%20May%2009.pdf (accessed 23rd January, 2020). 
15.  Findlay, W. P. K (1982), Fungi, Folklore, Fiction and Fact, The Richmond Publishing Company Ltd, Surrey. 
16.  Ibid., ref. 2. 
17.  Singh, J. and White, N. (1995), ‘Timber decay in buildings – research, remedies and reform’, Proceedings of Reconstruction and Conservation of Historical Wood Symposium, TU Zvolen. 
18.  Ibid., ref. 2. 
19.  Singh, J. (1993), ‘The biology and ecological control of timber decay organisms in historic buildings’, STREMA 93, 16th–18th June, Bath; Structural 

Repair and Maintenance of Historic Buildings III, pp. 311–327, Computational Mechanics Publications, Southampton. 

(20) Ibid., ref. 2.
(21) Singh, J. (1996), ‘Impact of indoor air pollution on health, comfort and productivity of the occupants’, Aerobiologia, Vol. 12, pp. 121–127. 

(22) Singh, J. (November/December 2019), ‘Mould Guard: Spore law’, RICS Built Environment Journal, pp. 48–50 

(23) Ibid., ref. 8.
(24) Ibid., ref. 9.
(25) Ibid., ref. 10.
(26) Ibid., ref. 11.
(27) Ibid., ref. 12.
(28) Singh, J. (1993), ‘Structural failures of timber in buildings; their causes, non- destructive inspection, monitoring and environmental control’, in Drdacky, M. (ed.), Proceedings of the Second International Conference on Lessons from Structural Failures, Anmer Society of Civil Engineers, Vol. 3, pp. 45–59. 

(29) ‘On the trail of a dry rot cure’ (September 1993), Daily Telegraph. 

(30) Bech-Andersen, J., Elborne, S. A., Goldie, F., Singh, J., Singh, S. and Walker, B. (1993), ‘The true dry rot fungus (Serpula lacrymans) found in the wild in the forests of the Himalayas’, Document no: IRG/ WP/93–10002. 

(31) White, N. A., Low, G. A., Singh, J., Staines, H. and Palfreyman, J. (May 1997), ‘Isolation and environmental study of “wild” Serpula lacrymans and Serpula himantioides from the Himalayan Forests’, Mycological Research, Vol. 101, No. 5, pp. 580–584. 

(32) Bech-Andersen, J., Elborne, S. A., Goldie, F., Singh, J., Singh, S. and Walker, B. (1993), ‘Egte Hussvamp (Serpula lacrymans) fundet vidtvoksende i Himalayas skove’ [‘Genuine house mushroom (Serpula lacrymans) found wild in Himalayan forests’], Svample, Vol 27, pp. 17–29. 

(33) Singh, J. (March/April 1995), ‘White NA: Dry rot and building decay: A greener approach’, Construction Repair, pp. 28–32. 

(34) Singh, J. (1996), ‘Environmental monitoring and control’, Building Conservation Directory, pp. 118–119. rot and timber decay: Don’t panic and poison yourself 

35. Singh, J. and White, N. (February 1997), ‘Timber decay in buildings: Pathology and control’, Journal of Performance of Constructed Facilities, pp. 3–12. 
36. For detailed information see Singh, J. (2000), ‘The Resistograph and the Non- Destructive Assessment of Timber Decay’, Environmental Building Solutions, available at https://www.ebssurvey.co.uk/ docs/Resistograph.pdf (accessed 23rd January, 2020). 
37. Singh, J. (May/June 1996), ‘Renovation – a thoughtful and multi-disciplinary approach’, Construction Repair, pp. 40–42. 
38. Singh, J. (August 1995), ‘Stop the rot’, Health & Safety at Work, pp. 14–16. 
39. Singh, J. and Nuss, I. (1995), ‘Environmental preservation of timber
    in buildings – a pragmatic approach’, Proceedings of Environmental Preservation of Timber in Buildings Conference, Dublin. 
40. Singh, J. (August 1994), ‘Rescuing a castle in distress’, Buildings & Facilities Management for the Public Sector, pp. 17–24. 
41. Singh, J. (1994), ‘Environmental conservation of medieval Telc Heritage Castle, Czech Republic’, Building Research and Information, Vol. 22, No. 4, pp. 222–227. 
42. Singh, J. (December 1994), ‘Protecting our common heritage’, Buildings & Facilities Management for the Public Sector, pp. 16–17. 
43. Singh, J. (1994), ‘Biodeterioration
    of building materials’, in Garg, K. L., Garg, N. and Mukerji, K. G. (eds), Recent Advances in Biodeterioration and Biodegradation, Vol. I, pp. 399–427. 
44. Lloyd, H. and Singh, J. (1994), ‘Inspection, Monitoring and Environmental Control of Timber Decay’, in Singh, J. (ed.), Building Mycology, Management of Health and Decay in Buildings, E. & F. N. Spon, London. 
45. Hutton, T. C., Lloyd, H. and Singh, J. (1991), ‘The environmental control of timber decay’, Building for a Future, Vol. 1, No. 4, pp. 16–22. 

(46) Hutton, T. C., Lloyd, H. and Singh, J. (1991), ‘The environmental control of timber decay’, Structural Survey, Vol. 10, No. 1, pp. 5–21. 

(47) Singh, J. (1991), ‘Non-destructive investigation’ Building Research & Information, Vol. 19, No.1, p. 20. 

(48) Singh, J. (1990), ‘Non-destructive Inspection of the Building Fabric’, in Bahns, T. (ed.), Building Pathology ’90, Proceedings of the 2nd International Conference on Building Pathology, Cambridge, Hutton + Rostron, pp. 215–216. 

(49) Singh, J. (1989), ‘The ecology and environmental control of timber decay in buildings’, Construction Repair, Vol. 3, No. 3, pp. 26–30. 

(50) Singh, J. (1989), ‘Environmental control of timber decay in buildings’, in Bahns, T., Hutton, T., Mayhew, L. and Mills, T. (eds), Building Pathology ’89, Proceedings of the 1st International Conference on Building Pathology, Oxford, Hutton + Rostron, pp. 108–121. 

(51) Dobson, J. R. and Singh, J. (1993), ‘Stopping the rot: Controlling timber decay in buildings without using pesticides’, Pesticide News, The Journal of Pesticide Trust, Vol. 20, pp. 6–8. 

(52) Dobson, J., Power, J., Singh, J. and Watkinson, S. C. (1993), ‘The effectiveness of 2-aminoisobutyric acid as a translocatable fungistatic agent for the remedial treatment of dry rot caused by Serpula lacrymans in buildings’, International Biodeterioration and Biodegradation, Vol. 31, pp. 129–141. 

(53) Singh, J. (November 1991), ‘Preventing decay after the fire’, Fire Prevention, Vol. 244, pp. 26–29. 

(54) Singh, J. (1989), ‘Investigation and advice on refurbishment of buildings after fire damage’, Construction Repair, Vol. 5, No. 5, pp. 25–28. 

(55) Ibid., ref. 40. (56) Ibid., ref. 41.