Timber Problems In Houses

Dry Rot

In the UK, the term 'dry rot' refers to outbreaks of wood decay by the fungus Serpula lacrymans. Unlike wet rot, for which relatively simple procedures are adequate for control, the successful remedial treatment of dry rot may require elaborate and sometimes very expensive control measures. It is important therefore, in the first instance, that an outbreak is identified correctly. There are a number of diagnostic features but sometimes the presence of several of them may be required for positive identification.

All types of wood rot can be difficult to detect in their early stages; this is particularly true of dry rot because it nearly always develops out of sight, often spreading behind panelling and plaster or beneath floorboards. Some indications of the possible presence of dry rot are softening of the wood in some areas, shrinkage and distortion and a distinctive 'mushroom' odour.

The principles, which govern successful eradication of decay, are prevention of further entry of dampness into the structure of a building, drying out the moisture which has already entered, and dealing with the fungus and repair of the damage that it has caused. These principles hold good whether the outbreak is small or extensive.

Wet Rots

The other types of wood-destroying fungi found on timber in buildings can be grouped conveniently under the term Wet Rots although some are known as 'brown rots' and some as 'white rots' because of their effect on the wood they are attacking.

All wet rot fungi require higher moisture contents than Serpula lacrymans, at least 30% moisture content, and many will achieve optimum growth and decay rates at between 45 and 60% moisture content. There is in fact a large number of fungal species that have been reported as causing wet rot decay of timber in buildings. Some initiate their attack in the standing tree, in the freshly felled log, or during seasoning. If such decayed timber is used in a building in a situation where it becomes wet, this type of decay may continue in the infected piece and can spread to adjacent timbers.

Insects

Most of the insects responsible for damage to timber are beetles. The adults lay eggs on the wood surface, in splits or in bark, and these hatch into active, grub-like larvae, which eat their way into the wood, creating tunnels. It is the feeding and tunnelling of the larvae that is largely responsible for damage to timber. The larvae of most wood-boring insects fill the tunnels with excreted wood pellets known as 'bore dust'. The size, shape and crosssection of the tunnels, and to a lesser extent the characteristics of the bore dust, are useful features for identification.

When fully grown, which usually takes between one and five years, the larvae undergo a transformation through a pupal stage to emerge from the infested wood as adult beetles. They leave characteristic emergence holes. The beetles do not themselves cause further damage though they can spread the infestation by egg laying.

Although the adult insects and larvae may be found on or in infested wood, their identification is difficult without experience and reference to detailed literature. Identification therefore relies usually on the characteristics of the damaged wood itself.