To initiate growth from a spore the wood must be physically wet; in other words it must be subject to a source of water ingress, e.g., leaking gutters, wood in contact with damp masonry, etc. In practical terms the wood must have a moisture content in excess of 28-30%. Spores will not germinate on dry surfaces or surfaces which are not suitably wet. In other words, unless the wood is wet dry rot cannot become initiated.

The origin of a dry rot attack is most likely to be associated with a severe source of water ingress, the most common being defective rainwater goods. Rising damp does not appear to be common as the originator of an infection although it will certainly support growth where infected wood is in contact with such dampness.

Like all wood destroying fungi dry rot flourishes in the slightly acidic conditions found in wood. But unlike the others it also flourishes under slightly alkaline conditions which explains the frequently encountered rapid growth behind and through old mortars and renders.

Growth rates of up to 4 metres per annum have been recorded; in other cases the organism may only have spread a few millimeters in the same period of time. However, Building Research Establishment give a figure of about 0.8 meters per year as a general purpose maximum growth rate (BRE Digest 299) and Coggins (1980) gives a general figure of about 1 meter per annum. Because there are large variations in growth rates, the age of an outbreak cannot be positively determined. The problem is further complicated since it is not always possible to tell if an outbreak is the result of a single outbreak or the coalescing of numerous outbreaks.

The spores are reported to remain viable for up to 3 years. They could therefore lay dormant until such times when conditions become suitable for their germination, that is, when any exposed wood surface on which they have landed becomes wet.

The mycelium can remain viable in damp masonry at around 18-20ºC without a food source for up to 10-12 months. But under the damp, humid conditions such as found in a cellar with temperatures of 7-8ºC, the mycelium may remain viable for up to 9-10 years! If untreated wood is put in contact with damp infected masonry there is always the potential for the new wood to become infected.

Control Of Dry Rot

The principles for the control and eradication of dry rot are outlined as follows:

Primary Measures

The most vulnerable feature of the fungus is it requirement for water, and it is the control and elimination of this essential requirement that forms the fundamental measure for the control and elimination of dry rot.

• Locate and rectify the source of water causing and maintaining the rot.
• Promote and maintain rapid drying conditions.

The removal of the source of water is the first point of attack. It is therefore absolutely essential to stop further water ingress. This action alone will eventually control and eliminate the activity. Indeed, it is the fundamental measure in eradicating the organism. Included in this action is the promotion and maintaining of rapid and good drying conditions.

Secondary Measures

• A specialist contractor such as Lifecote will fully understand the factors involved Please note: where dealing with historic properties and where it is deemed necessary to keep as much of the historic timbers as practically possible then it is essential that dry techniques are used. This WILL require careful monitoring of both conditions and the state of the rot; such practices should only be conducted by specialist professionals in the conservation of historic timbers.