Timber is one of the oldest construction materials known. It has and will continue to be within the building industry for the foreseeable future. Timber is a remarkable material, which can be fashioned by cutting, moulding, stripping, etc. Used in many ways both decorative and functional. Timber does however have one major drawbacks, it is of course susceptible to deterioration by both attack from wood boring insects and fungal decay. This is particularly relevant where damp conditions exist.
Timber can be classified into two categories, hardwood and softwood. Hardwood timbers are produced from broad leafed trees such as teak, mahogany, elm and oak. Whilst softwood is produced from coniferous trees such as spruce, fir and pine, it is a misconception to believe that hardwood is always more durable than softwood, indeed the heartwood of some hardwood timbers such as teak and oak is extremely durable. The heartwood of others is rated as perishable such as in beech. Many older properties will contain mainly hardwood structural timbers, buildings constructed since about 1800 will in general have more softwood structural elements. The main enemies of timber in this type of situation are, attack by wood boring insects and decay as a result of wood rotting fungi.
Wood Booring Insects
The term ‘woodworm’ is often used to identify a variety of species of beetles the larvae of which bore into timber to feed causing structural weakening of the timbers where an infestation has been allowed to survive. The characteristic flight holes are formed by the adult insect as it bores its way out of the timber in order to mate or reproduce. The lifecycle of the various species follow the same pattern e.g., egg, larvae, pupae, adult insect. However, the span of the cycle from egg to adult beetle varies considerably from one insect to another.The more common wood boring insects in the UK are:
Common Furniture Beetle (anobium punctatum)
This is by far the most common and widespread of wood boring insects in the country, frequently found in older furniture and all constructional timbers, particularly around loft access, timbers in contract with solid walls, understair areas, cupboards and other areas that may have been affected by damp. Sapwood is preferred as with most species, but heartwood is also vulnerable to infestation by this beetle.
Death Watch Beetle (xestobium rufovillosium)
Death watch beetles infest hardwood (mostly oak) and softwood in contact with infested hardwood if some degree of fungal attack is present. It is often found in historic buildings where large quantities of oak or elm have been used structurally. The presence of death watch beetles can often be associated with damp conditions and fungal decay, although the infestation can continue, albeit slowly, in dryer timber.
Those timbers of particular concern are embedded wallplates, joist ends, lintels and any other timbers built into the fabric of the building. Damage is often extreme in concealed bearing ends of timbers inserted into damp walls. In conjunction with fungal attack, this infestation may hollow out entire centres of large sections.
Wood Boring Weevil (euophryum confine)
Wood boring weevils are unusual amongst wood boring insects in that both the larvae and the adult insect bore into timber, also the ability exists for several lifecycles to be completed in a single year in favourable conditions. This beetle attacks decayed softwoods and hardwoods in damp conditions. Poorly vented ground floors, cellars, and wood in contact with damp floors or walls are particularly vulnerable. The beetle will also attack plywood in these conditions.
House Longhorn Beetle (hylotrupes baljulus)
Widespread throughout Europe, in the UK this beetle is confined to the south of England and is locally referred to as Camberley or Surrey beetle. This beetle is recognised as one of the most destructive beetles and a single larvae of this species can do more damage within a building, usually to roof timbers, than several dozen larvae of the common furniture beetle.
Upon identification, this infestation is a beetle attack, which must be notified to the Building Research Establishment who keep records of such attacks. Once identified, it is strongly recommended that a Structural Engineer / Surveyor be employed to assess the structural integrity of timbers within the area concerned.