Woodworm in a Survey Report: Active Infestation or Old Damage?
"Evidence of woodworm activity noted in roof timbers" is a line that appears on a huge proportion of UK property surveys, especially anything with exposed timber — lofts, floorboards, older staircases. It sounds alarming, but the reality is that most UK homes with any age to them have some historic woodworm damage, and the real question is whether it's active or long dead.
Why Woodworm Is So Common
"Woodworm" isn't one species — it's a general term for several wood-boring beetles whose larvae tunnel through timber, most commonly the common furniture beetle in the UK. Untreated softwood roof timbers, floorboards and joinery are naturally vulnerable, particularly where there's been any past damp (the larvae favour timber with slightly elevated moisture content). Because so much UK housing has some exposed softwood timber somewhere, it's one of the most frequently flagged items on a survey — and one of the most frequently over-treated.
Active vs Historic: The Key Distinction
Signs of historic, inactive damage:
- Exit holes (small, roughly 1–2mm round holes) that are darkened or discoloured with age, matching the surrounding wood's patina
- No fresh, pale wood dust (frass) around or beneath the holes
- Timber that's structurally sound when tested (a bradawl or knife shouldn't sink in easily)
- Often found alongside evidence of a historic treatment (timber showing old staining from previous chemical treatment)
Signs of active infestation:
- Fresh exit holes with pale, clean-edged wood visible, not weathered
- Fine, pale wood dust (frass) actively accumulating beneath the timber — this is the clearest single sign
- Adult beetles found (they emerge April–September, so a spring/summer viewing is more likely to show live evidence)
- Soft or crumbly timber when tested
Reading the Survey Language
"Historic evidence of woodworm, no signs of current activity" — the best-case wording. This usually means no action beyond monitoring is needed.
"Evidence of woodworm activity, unable to confirm if active" — genuinely ambiguous, often because the survey happened outside the beetles' flight season or access was limited. Worth a closer look before you commit to a treatment cost you might not need.
"Recommend timber specialist inspection" — the surveyor wants a closer, more invasive look (potentially including probing timber structurally) than a standard visual survey allows.
"Structural timber shows signs of significant weakening" — the more serious version, suggesting the woodworm damage may have gone beyond cosmetic and affected the timber's load-bearing capacity, warranting a structural engineer's opinion, not just pest treatment.
Realistic Costs
| Job | Typical cost | Worth knowing |
|---|---|---|
| Timber specialist inspection | £150 – £350 | Worth it before committing to any treatment quote |
| Chemical woodworm treatment (per room/loft area) | £300 – £800 | Standard fix for confirmed active infestation |
| Whole-property treatment (larger period house) | £1,500 – £3,500 | Where infestation is widespread, not localised |
| Structural timber replacement (per joist/section) | £200 – £600 | Where damage has genuinely weakened load-bearing timber |
| Full roof structure timber repair (significant damage) | £4,000 – £12,000+ | Rare, but worth budgeting for if a structural engineer flags significant section loss |
What to Do Before You Offer
Don't assume "woodworm" automatically means a big bill. Ask whether the survey found active or historic evidence, and if it's ambiguous, get a timber specialist to check before you factor a treatment cost into your offer — many properties with old exit holes need nothing at all.
How Chat to Your Builder Helps
For £59, we'll look at your survey's timber findings and any photos, help you judge whether you're looking at old damage or something active, and give you realistic costs either way.
We've helped buyers assess timber issues on period properties across London, York, Canterbury, Truro and Bath. See our related guides on wet rot vs dry rot and timber treatment guarantees.
Book your consultation today and get a clear read on what your survey's woodworm findings actually mean.
Frequently asked questions
Does every property with woodworm exit holes need treatment?
No. If the holes are old, discoloured and there's no fresh frass (wood dust) or soft timber, it's likely historic and inactive. Treatment is generally only needed where there's evidence of current, active infestation.
Why is it harder to confirm active woodworm outside summer?
Adult wood-boring beetles typically emerge and fly between April and September, so a survey done in autumn or winter is less likely to catch direct evidence of live beetles, making the 'active vs historic' judgement rely more on frass freshness and timber condition.
Can woodworm affect a property's structural integrity?
In severe, long-untreated cases, yes — enough tunnelling can weaken load-bearing timber. This is uncommon but is exactly why significant or ambiguous findings are worth a specialist inspection rather than assuming it's cosmetic.
Work it out yourself
Free tools built on real 2026 builder rates. No sign-up, no email.