Woodworm is a term used for the larval stage of several wood-boring beetles whose grubs tunnel through timber, leaving behind a network of galleries and the familiar round exit holes. In most UK properties it is a cosmetic nuisance rather than a structural emergency — but knowing how to identify the species, assess whether an infestation is active, and choose the right treatment will save you from either unnecessary expense or from ignoring a problem that could genuinely weaken timbers over time.
Which Beetles Cause Woodworm in the UK?
Four species are commonly encountered in UK homes:
| Species | Hole Diameter | Prefers | Common Location | Risk Level |
|---|---|---|---|---|
| Common Furniture Beetle (Anobium punctatum) | 1–2 mm | Sapwood of softwood and hardwood | Floorboards, joists, furniture, roof timbers | Low–moderate |
| House Longhorn Beetle (Hylotrupes bajulus) | 6–10 mm (oval) | Sapwood of softwood | Roof timbers (mainly SE England) | High — can cause structural failure |
| Deathwatch Beetle (Xestobium rufovillosum) | 3 mm | Hardwood, especially oak; often already decayed | Old hardwood floors, historic beams | Moderate–high |
| Powder Post Beetle (Lyctus spp.) | 1.5–2 mm | Hardwood sapwood; high starch content | New hardwood: oak flooring, ash, elm | Low–moderate; mainly in new timber |
The Common Furniture Beetle accounts for the overwhelming majority of woodworm encountered in residential properties. It affects both softwood and hardwood, prefers damp or slightly humid conditions, and exits the timber as an adult beetle between May and August. Its small exit holes (1–2 mm) are what most people recognise as woodworm.
The House Longhorn Beetle is more serious but geographically restricted in the UK — it is mainly found in parts of Surrey, Hampshire, and a few other areas in the south-east. It can cause significant structural damage to roof timbers and is the only UK woodworm species where the Building Regulations historically required treatment as a matter of course in certain areas.
Is the Infestation Active?
Distinguishing active from old (dead) woodworm is critical before spending money on treatment.
Signs of active woodworm:
- Fresh, clean, pale-coloured exit holes (not filled with dust or discoloured)
- Fine, creamy-yellow powdery dust (frass) in or below the holes — it looks like sawdust but finer
- Small oval beetles (the adult Anobium punctatum is 2.5–5 mm long, reddish-brown) appearing in the room between May and August
- The frass still feels soft or powdery, not compressed or discoloured
Signs of old, inactive infestation:
- Exit holes with dark or dirty edges (oxidised over time)
- No frass, or frass that is grey/dark and compressed
- No beetle sightings in several seasons
Old woodworm holes are extremely common in Victorian and Edwardian timber — the vast majority of Victorian floorboards have some woodworm holes from historical infestations that have been dead for decades. Treatment of inactive woodworm in non-structural timber is unnecessary.
When Is Treatment Necessary?
Treatment is warranted when:
- The infestation is active (fresh holes and frass present)
- The affected timber is structural — joists, rafters, purlins, ridge boards, floor bearers
- The affected area is significant (more than one or two isolated exit holes)
Treatment is not urgently necessary when:
- The woodworm appears inactive
- The timber is non-structural (furniture, skirting boards, decorative panelling)
- The affected area is a small section of isolated holes without current frass
Treatment Options
DIY Treatment
For non-structural timber and confirmed active but minor infestations, proprietary woodworm killer products are widely available. These are typically permethrin-based or boron-based liquids applied by brush or spray. Apply generously to all surfaces and into holes, allow to soak in, and repeat as directed (usually two coats, 30 minutes apart).
DIY treatment is suitable for: furniture, skirting boards, non-structural panelling, small areas of floorboarding where the boards can be lifted to treat the underside and the joist tops.
DIY treatment is not suitable for: roof timbers (access and coverage are the issues), whole-floor treatment of a suspended ground floor (impractical and inadequate coverage), or structural damage requiring repair rather than treatment.
Professional Treatment
Professional treatment uses two main approaches:
Permethrin spray treatment — the most common method, where a professional applies a water-based permethrin insecticide by spray or brush to all accessible timber surfaces. In roof spaces this typically means treating all visible softwood. Vacating the property during application and for a period after is required. Treatments usually come with a 20–30 year guarantee backed by insurance.
Boron-based treatment — boron salts (usually disodium octaborate) are applied as a gel, paste, or liquid. Boron is less toxic to mammals than permethrin and is considered preferable in occupied homes, around food preparation areas, and where children are present. It is also effective against fungal decay. Boron treatment is slower-acting and requires the timber to have some residual moisture to carry the boron into the wood, so it is less suitable for very dry softwood.
Fumigation (methyl bromide or phosphine) — used only in extreme cases or for heritage buildings where spray penetration is inadequate. Requires complete evacuation and specialist contractors.
Structural Damage Assessment
Where woodworm has been active over many years — particularly Deathwatch Beetle in old oak or House Longhorn in roof timbers — structural timber may have been weakened. Before treatment, a structural engineer or chartered surveyor should assess whether any timber members need sistering (adding a new joist alongside a damaged one), reinforcing, or replacing entirely. Treatment alone will not restore the strength of heavily damaged timber.
Cost Guide
| Work | Typical Cost (2026) |
|---|---|
| DIY woodworm spray (materials only) | £15–£50 per tin; £50–£200 for a typical room |
| Professional treatment — one room | £200–£500 |
| Professional treatment — whole house (roof + floors) | £400–£1,200 |
| Professional report / survey | £150–£350 |
| Structural timber replacement (per joist, if needed) | £200–£600 per member |
Prevention
Woodworm prefers damp timber with moisture content above 18%. Reducing humidity in roofspaces and subfloor voids is the most effective long-term prevention. Ensure adequate cross-ventilation in roof spaces (typically one vent per 150 m² of ceiling per BS 5250:2011 recommendations) and maintain ground-level airbricks in suspended floor voids. Treating timbers with a preservative before installation (pressure impregnation or surface treatment) is standard on new structural softwood used externally or in contact-with-ground situations.
Any timber salvaged for reuse — particularly reclaimed floorboards or structural beams — should be inspected carefully for signs of active woodworm before installation, and treated if any doubt exists.
Choosing a Contractor
Use a contractor registered with the Property Care Association (PCA) or who holds a CSRT (Certificated Surveyor in Remedial Treatment) qualification. Request a written survey report identifying species and extent of infestation before accepting a treatment quotation. Be wary of surveys conducted by companies offering treatment, where there is an obvious incentive to over-specify.
