Timber frames

Timber decay in these buildings can reach substantial parts of the frame. The furniture beetle in particular likes oak, from which most frames are made.

For surveyors, the most difficult and critical assessment in respect of the activities of wood-boring larvae is to determine if the outbreak is still live, and how deep the infestation is. If the infestation is dormant and the structure proves to be sound, then there is little evidence to suggest that large-scale works will be cost effective or historically prudent. Keeping the timber's moisture content at the correct level will greatly decrease the risk of further attack.

There are some simple methods that can help determine whether intervention is necessary. The application of acid-free tissue paper over a suspected area can reveal if fresh exit holes are being created, suggesting that the infestation is live. This is best carried out in spring, when the larvae exit the wood as adults. Monitoring is a fairly long process, best carried out over several months for conclusive results, but the method is simple to execute and quite effective.

Closely observe the edges of exit holes. If they are rough or raised, this indicates they are new, or at least created within a season. If they are smooth-edged, it is more likely that they are older. Look for dust below the holes, as this too is evidence of recent activity. If any work has been undertaken in the roof, however, residual dust on beams and joists may be from these activities.

Once an infestation has been identified, the primary remedies are to either poison or dry the food supply, or kill the larvae. Treating timber locally is not generally recommended, as any part of a structure can be affected. However the toxicity of any product used, and the extent of replacement to damaged timber, needs to be detailed carefully.

Some insecticides are being phased out of use. Also some authorities argue that prevention is more about reducing moisture content and making the timber too dry for larvae to live in. There are specialist fumigation and heat processes, used mainly on high-profile properties, but this is very intrusive, and the building's occupants will need to be re-housed while it is carried out. This can make the process prohibitively costly.

In roof spaces of occupied houses, take care when planning the works, as items in the roof space may need to be removed before contractors are sent in. It may also be necessary to keep the area secure for a while before items can be returned. Guarantees and insurance policies may conflict with conservation principles, and it is wise to check if a client's policy is likely to insist on a particular form of treatment, regardless of the extent of the defect.

If treatment is undertaken, for future reference, it is useful to apply a plate to the beams indicating the date and type of remedy.