'Dry rot' (Serpula lacrymans) is a wood destroying fungi, which requires the presence of moisture in timbers during its initial stages of growth. Water that penetrates the wood allows bacteria and micro fungi to colonise. These break down the cell structure of the timber and the wood becomes more porous which allows it to absorb more moisture. Dry rot can begin by a minute spore landing on the damp timber. The spore grows and forms hyphae (fine filaments), which secrete enzymes and break down the wood. The breaking down of the wood releases sugars which, when respired with air produce carbon dioxide, water and energy for the growth of the fungus. When the wood is broken down and utilised for food, shrinkage, loss of weight, loss of strength and cracking will occur. It is the shrinkage, which causes the typical cuboidal cracking of the timber, often associated with the presence of dry rot. As the dry rot fungus grows the hyphae develops into a large mass, known as mycelium. The mycelium is white and cotton wool like, although in some conditions it may be silky grey and tinged with yellow and lilac patches. Within the mycelium, strands will form. These strands can penetrate brickwork, pass over inert substances and colonise other timber in the vicinity. It is the ability for the fungus to travel away from the food source, which makes dry rot so destructive. Advanced growth of the fungus will create a fruiting body, which resembles a fleshy pancake. Large numbers of spores frequently collect around the fruiting body and form a red ‘dust’. The ‘dust’ (spores) can often be visible in areas where there is no significant attack of dry rot.
Professional diagnosis is essential to establish the extent of the dry rot outbreak in order to minimise disruption. Treatment of dry rot may often require the removal of structurally weakened timber(s) and wall plaster, together with extensive reinstatement works. However, the first priority is always to eliminate the water source causing the attack and to promote the rapid drying of the property.
Any timbers to be replaced should be industrially treated and isolated from contact with masonry by a suitable waterproof membrane or joists hangers. Skirting boards, architraves, door frames, etc., may also have to be removed and replaced.
Fungicidal sterilisation treatments are sometimes considered necessary to control the attack and reduce the chances of re-infection.
Re-plastering is required to a suitable specification. Additional airbricks may also be required to sub floor areas.