Dealing with Woodworm

Q: I intend to buy an old property which shows signs of woodworm. My surveyor suggests that the woodworm is ‘inactive’ and may have been treated. I’m not so sure — what should I be looking for, and should I be concerned?

- L Burgress, Via Email

Peter Glover answers: There are a number of insects that lay eggs in small cracks in timber which then hatch into grubs and go on to bore holes in woodwork. The most frequently seen in Britain is the common furniture beetle (Anobium Punctatum) which generally has a three-yearly lifecycle with the small beetles laying eggs in May or June. The grubs bore into the wood and, when they eventually emerge, this results in small holes – around 1.5mm in diameter – with deposits of bore dust beneath. The emerging insects then fly and lay eggs elsewhere.

If there is an active attack, there will be new holes – smooth and clean inside – with deposits of fine dust beneath. Holes which are old and dirty inside, with no signs of recent dust, are likely signs of old, inactive woodworm.

In the past it has been quite usual for surveyors to recommend the extensive chemical treatment of timbers in a house where woodworm is found. Some chemicals used back then, such as Lindane, are now banned for health reasons and there is a general consensus amongst surveyors that the use of chemicals should be minimised where possible. So, just because you find a few woodworm holes under the stairs or in an isolated floorboard, does not mean that all the timbers in the house need to be sprayed.

No living thing can survive in the total absence of moisture, and much damage caused by woodworm and rot to timbers can be avoided by good design — ensuring that timbers are kept dry, well ventilated and free from condensation. Provided that timbers are not structurally weakened, then old woodworm holes should not be a cause for worry. Check timbers from time to time for any signs of new holes and new bore dust. If nothing new appears, there is no need to spray the timbers with insecticide preservatives. In old houses and barn conversions, lots of old holes in the timbers may actually add to the charm and character.

If you find much larger holes – 2-3mm in diameter – in old oak or other hardwood timbers, then this could be the death watch beetle — a particular problem in old buildings where timbers are damp. The death watch beetle is so-called because the insects make a loud ticking noise at night, and our superstitious ancestors thought that this was an omen that someone in the house was about to die. If the house was damp and full of rotten timbers, this apparent connection between the ticking sound and pneumonia certainly made some sense.

Another insect, the house longhorn beetle, has ovalshaped flight holes 3-9mm in diameter — and is potentially very destructive. This insect first became a problem in Weybridge, Surrey during the 1960s, but is now spreading further afield. If you suspect that either this insect or the death watch beetle are active then you do need to take expert professional advice. Try property-care.org to search in your area.

Peter Glover is an experienced Chartered Surveyor working in London, and author of Building Surveys: Seventh Edition (Elsevier Ltd; elsevier.com, £24.99)

Active or inactive?

If woodworm is a particular concern when buying a property, organise for a specialist timber consultant, such as ATICS (atics.co.uk), or surveyor from, for example, Anderson Surveys (andersonsurvey.co.uk) to conduct an independent investigation.

If woodworm is a worry in your existing home, then try ringing exit holes with indelible ink. This will enable you to identify whether any new holes have been created.

Affected floorboards or joists will need to be cut back and replaced. The underside of the new boards and any nearby joists should also be treated.

Further reading:

• Restoring Timber Floors
• Ageing New Timber
• How to Assess a Property for Renovation