You won’t have any trouble finding an expert to advise you if you have a dry rot problem in a building you are restoring or converting. All you have to do is to take a look at the Yellow Pages and lift the phone. The trouble with this approach, however, is that it can cause more problems than it will solve. Over the years many remedial companies have been accused of being trigger happy with chemical sprays when all that was needed was a more gentle approach, possibly involving no spraying at all.

In these health-conscious times such tactics are widely out of favour and many remedial companies now take a more holistic approach. This involves the classic three-pronged method of removing the affected timber, ventilating the area where the rot has occurred, and treating the infected area with insecticide and fungicide.

The last is only used if it is really necessary. However one of the main problems can be determining whether the crazed and flaky brown timber is in fact suffering from dry rot or not. “The diagnosis is all,” says Robert Demaus of Demaus Building Diagnostics, specialists in the holistic approach towards curing decay in historic buildings. “The truth is that dry rot is pretty uncommon today. The circumstances in which it occurs are very specific: it needs just the right combination of moisture and warmth and nowadays we tend to run our houses at such a high temperature that this reduces the risk of dry rot and other forms of fungus.”

The classic symptoms to look for in dry rot often mistaken for wet rot are a fleshy pancake-shaped brown fungus called a sporophore which can sometimes measure more than 1m in width. It is accompanied by a distinctive mushroom odour. A sporophore less than 1m2 can produce more than 50m spores per minute for several days. It is best to use an expert to identify the fruiting body and if you are unable to find such a person the wisest move would be to remove a sample of the rot and submit it for analysis.

“Basically if you find the source of the damp and introduce measures to dry the building you will be able to control dry rot for ever,” says Dr Jagjit Singh of Environmental Building Solutions, another acknowledged expert, who takes a strongly anti-chemical line. “Once the moisture content of the timber falls below 20 per cent, dry rot will gradually become dormant and die within about a year.”

Robert Demaus is equally emphatic about the need to find the cause of the dry rot outbreak but he believes there are circumstances in which chemical treatment might be justified. “The classic case is three or four years after a major fire and spores that might have been latent for years are activated as all the wet poured in to control the fire dries out,” he says. “When the moisture content reaches certain levels there is a risk of fungal attack.

“Even then there has to be timber involved for dry rot to occur. If it is the floor joists going into the chimney that are the problem an area often prone to water penetration there are isolation techniques that can be used. I usually only recommend chemical treatment if you cant get the moisture content down by other means within a reasonable time.”

The British Wood Preserving and Damp Proofing Association has some 200 members among the 2,000 or so companies in the UK that undertake this sort of work and has at times been under fire from those who take a holistic approach for the over-use of chemical sprays. Director Dr Chris Coggins says: “Member companies adhere to set standards. This includes tracing all fungus until its origin and limit of attack is ascertained, and also using treatments such as drying which might not necessarily involve chemicals. In any case statutory regulations require a proper assessment of any substance hazardous to health before it is used and we provide guidance to our members on this.

“However it is still true that most of the remedial companies are still unregulated and that cowboy operators can set up in business with no proper knowledge of what they are undertaking. My advice to householders is to make sure the outbreak of rot is correctly diagnosed, preferably by a specialist in this field with a qualification in remedial treatment, and to go to one of our members, who will make a proper diagnosis before recommending expensive and often invasive treatments that may be unnecessary.”

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