Timber is a natural material, and in nature is broken down by both fungi and insects (mostly beetles) and recycled.
Unfortunately, when we use timbers in buildings, we want them to last with minimum expense, so these natural processes are not wanted. Unlike our ancestors, we do not want to build a new shelter at frequent intervals. Fortunately, most forest beetles will not live in a dry house. Use of large section timbers will allow a certain amount of the outer sections of a tree trunk (the sapwood) to be consumed by beetle attack without reducing strength below an acceptable level, but significant fungal attack cannot be allowed, as fungi attack all sections of a piece of timber. Choice of timber species is important as some are more resistant to beetle and fungus attack than others, and some beetles and fungi will only attack certain timber species.
Timber surveys involving beetles therefore need to identify the species responsible for an attack, to determine whether chemical or other treatment is appropriate. More importantly, where fungal decay is found, it is essential to distinguish between true Dry Rot (Serpula lacrymans) and the various Wet Rots. Because Dry Rot can spread through and over inert materials such as masonry, control measures are more extensive and disruptive, and therefore more costly. Such cost is not necessary when dealing with Wet Rots – though it is important to recognise fungal species which do not feed on timber, which may still be found in some situations such as flood or major leaks.
The role of moisture in timber attack by fungi and some insect species is very important. A timber survey must therefore include an inspection for sources of moisture, to determine areas at risk, as well as identifying insects and fungi which may be present. An external inspection is therefore needed to determine building defects which will allow dampness to penetrate the structure, or for damp conditions to arise. A through flow of air beneath ground floor timbers is important in preventing fungal decay, so air bricks need to be present in appropriate locations.