Woodworm is the catch-all term for several wood-boring beetles whose larvae tunnel through structural and furniture timber. In Cornwall — old granite-and-cob cottages, listed buildings, damp roof voids, cool understair cupboards — woodworm is common enough that most period properties have evidence of historical activity. The question that drives most surveys is: is this active and does it need treating, or is it old and harmless? This guide gives the honest 2026 cost ranges and the decision framework.
The short version
- Woodworm survey only: £80-£250
- Standard whole-property treatment (typical 2-3 bedroom Cornwall house): £800-£1,200
- Specialist treatment per room: £1,250-£1,750 (for severe or sensitive cases)
- Fumigation (worst-case, sealed structures): £500-£1,000+
- DIY boron-based products (mild cases, accessible timber): £15-£42 supply, plus your labour
- Pre-purchase survey for a Cornwall property (mortgage-driven): £150-£350
Cornwall pricing tracks UK averages because the products and methods are standard; the local variable is the prevalence of older buildings needing more sensitive specialist treatment.
What woodworm actually is
Several beetle species; the practical UK picture:
- Common Furniture Beetle (Anobium punctatum) — by far the most common cause of UK woodworm. Adults 2.5-5mm, dull reddish-brown. Round exit holes 1.5-2mm wide. Frass (wood dust) is fine and lemon-shaped under magnification.
- Deathwatch Beetle (Xestobium rufovillosum) — larger species, 5-7mm adults. Exit holes 3-4mm. Mostly attacks hardwoods (oak, chestnut) particularly where there's been historical damp. Cornwall church roofs, oak-beamed listed buildings.
- House Longhorn Beetle (Hylotrupes bajulus) — rare in the UK, mostly in softwoods in southern counties. Significant structural pest where it occurs. Oval exit holes 6-10mm.
- Powderpost Beetle (Lyctus brunneus) — attacks freshly-sawn hardwoods with high starch content; often introduced in imported timber. Exit holes 1-2mm.
- Wood-boring Weevils — secondary infestation in already-rotten timber. Address the damp, not the weevils.
The species matters because treatment and urgency differ. A Cornwall surveyor should always identify which beetle is involved, not just "woodworm".
Active vs historical — the critical distinction
Most Cornwall period properties have woodworm exit holes somewhere. That doesn't mean active infestation. The distinguishing signs:
Active infestation:
- Fresh frass (wood dust) below exit holes — clean, pale colour, often piled in small cones
- Pale, sharp-edged exit holes — newly emerged, no patina
- Dead adult beetles found on window sills May-September (the emergence season for common furniture beetle)
- Live larvae visible if a damaged section is cut
- Tunnels packed with fresh frass when probed
Historical (non-active):
- Exit holes are dark, weathered, with the same patina as the surrounding timber
- No fresh frass — any dust in or below holes is grey, dirty, mixed with cobwebs and other detritus
- Filled or painted-over holes
- No dead adult beetles found seasonally
This is where a competent surveyor pays for themselves. A reputable Cornwall woodworm surveyor will tell you when to walk away from treatment because the evidence is historical, not active.
What drives Cornwall woodworm
Three main risk factors:
- Moisture content. Common furniture beetle prefers timber with moisture content of 14-20%. Below 12% (well-ventilated, heated buildings) infestations decline naturally. Above 20% (damp, unheated, sub-floor voids) populations thrive.
- Timber species. Sapwood is much more vulnerable than heartwood. Pine, fir, beech, willow, alder are favoured. Oak heartwood, mahogany and properly-seasoned tropical hardwoods are generally resistant.
- Age and exposure. Older softwood roof and floor timbers in unheated voids are the typical Cornwall hotspot. Newer construction with treated timber is much less susceptible.
Cornwall-specific patterns:
- Granite cottages with original lath-and-plaster ceilings and Victorian softwood joists — common hotspot
- Sub-floor voids in older terraced housing — humidity often high, ventilation poor
- Unheated holiday lets — moisture variation through occupancy cycle
- Listed buildings with original oak (deathwatch beetle risk where historical damp exists)
- Roof timbers in poorly-ventilated lofts
What a treatment actually involves
The standard process:
- Survey visit. Inspector examines affected timber, identifies species, assesses moisture content (moisture meter), distinguishes active vs historical, writes a report with recommendations.
- Preparation. Affected timber is brushed/vacuumed to remove surface debris. Loose paint, varnish or surface treatment may need removing where it would prevent product penetration.
- Application. Professional-grade insecticide — typically permethrin-based for active infestations — applied by brush, spray or injection into exit holes. Boron-based products are used for milder cases and where lower toxicity is required.
- Coverage. All accessible surfaces of affected timber, plus 1-2m beyond visible activity (in case adjacent timber is also infected at sub-surface level).
- Drying and ventilation. Treated areas should be ventilated for several days; some occupancy restrictions during this window.
- Follow-up. Typically a 12-month return visit to check for new activity. Reputable companies offer 10-30 year guarantees on whole-property treatments.
When DIY is fine vs when it isn't
DIY likely fine:
- A single piece of furniture with localised, low-grade activity
- A small accessible area of timber (a shed beam, a single floorboard)
- You can apply boron-based product (lower toxicity, easier handling) to the affected surfaces multiple times
- You're prepared to monitor for 12-24 months to confirm clearance
Professional treatment justified:
- Whole-property activity — multiple rooms, structural timber, roof voids
- Listed building (specialist sensitive treatments required)
- Deathwatch beetle or House Longhorn beetle (species-specific approaches needed)
- Mortgage-driven (lenders typically require professional treatment with guarantee)
- Pre-sale (buyers want certified treatment, not DIY)
- Active damp problems contributing — you need a surveyor who addresses both
What about the damp first?
The single most useful thing you can do for woodworm is fix the damp. Common furniture beetle thrives at 14-20% moisture content. Below 12% it declines. Reducing moisture content via:
- Improving ventilation (sub-floor airbricks, loft venting)
- Heating regularly (rather than letting an unoccupied holiday let stay cold and damp)
- Fixing roof leaks, gutter overflows, blocked downpipes
- Treating rising damp where present
- Insulating to reduce condensation
...will often reduce woodworm activity dramatically without chemical treatment. For mild cases, addressing the damp is the proper first intervention. For severe or established cases, treat AND address the damp.
Listed buildings and sensitive specifications
Cornwall has many listed buildings where conventional permethrin-based treatments may be inappropriate:
- Original timber finishes (limewash, beeswax, oil-finishes) may interact poorly with modern actives
- Listed Building Consent may be required for treatments affecting historic fabric
- Specialist conservation-grade products (boron-based, low-VOC, reversible where possible) exist for sensitive cases
- Treatment specifications often need approval by the local Conservation Officer
Always ask the surveyor whether they have experience with listed buildings before booking — generic woodworm specialists may not be familiar with conservation constraints.
Pre-purchase Cornwall property — survey priorities
If you're buying a Cornwall property and the structural survey flagged possible woodworm:
- Commission a specialist timber and damp survey (£150-£350) — separate from the structural survey
- Ask the surveyor to identify species, distinguish active vs historical, and quote treatment costs if needed
- Use the survey to negotiate on price if active infestation is confirmed
- For listed or unusually old properties, ask whether the surveyor has conservation experience
- Don't accept "possible woodworm noted" in the structural survey as the end of the conversation
Get a Cornwall woodworm survey
Submit your postcode on the quote form and mention "woodworm survey" in the notes. For listed buildings or conservation-sensitive properties, flag this. We match you with Cornwall surveyors and woodworm specialists with relevant building-type experience. See related: full Cornwall pricing, carpet moth treatment, Bodmin, Launceston.