How to Price Timber Treatment: Woodworm, Wet Rot, Dry Rot and 30-Year Guarantee Margins

Quick Answer: A typical residential woodworm treatment of a 30–50m² roof void or floor area prices £450–£1,200 in 2026 including 20–30 year insurance-backed guarantee. Wet rot localised treatment prices £280–£780 per affected area. Dry rot (Serpula lacrymans) treatment is materially different — outbreaks require eradication of all infected timber, sterilisation of masonry, and isolation of moisture source, typically £1,400–£4,800 for a moderate domestic outbreak. Mis-diagnosis between wet rot and dry rot is the single biggest source of customer complaints — the protocols and costs are very different.

Summary

Timber treatment is a diagnostic-led specialist trade. The pricing is driven less by labour and material than by liability and guarantee — a 30-year insurance-backed guarantee on a £600 woodworm treatment carries £80–£140 of insurance loading, and the guarantee is what the customer is buying. The Property Care Association (PCA) is the trade body, and CSRT-qualified surveyors carry professional indemnity for diagnostic accuracy. A £150–£280 surveyor visit before treatment is the single most important investment in this trade — the treatment fee depends entirely on accurate identification of the species and extent of the problem.

The category splits sharply between three distinct problems. Woodworm (common furniture beetle Anobium punctatum being 90% of UK cases, plus death watch beetle Xestobium rufovillosum, house longhorn Hylotrupes bajulus, and powder post beetles) is treated by spray-applied permethrin or boron-based fluids on accessible timber surfaces. Wet rot (Coniophora puteana most commonly) is the reaction of timber to chronic moisture above 28% — fix the moisture source, replace failed timber, treat surrounding sound timber as a precaution. Dry rot (Serpula lacrymans) is the dangerous one — it can spread through and behind masonry to colonise distant timber, requires extensive eradication, and a missed outbreak resurfaces years later as a much larger problem.

The 1990s and 2000s saw aggressive over-treatment by some operators, with blanket woodworm treatment of properties showing only old, dead infestation. The modern PCA approach is risk-based: identify active infestation by frass analysis and exit-hole condition, treat only affected timber where active infestation is confirmed, and educate the customer on the distinction between historic (treated, dormant) and active (treatable, moving) damage. Pricing the diagnosis correctly is more important than pricing the treatment.

Key Facts

Quick Reference Table

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Job type Scope Programme Total fee 2026
Woodworm treatment (single room) 30m² timber surface 1 day £380–£780
Woodworm treatment (whole loft) 50–80m² timber 1–2 days £650–£1,400
Woodworm whole-house spray 150–250m² timber 2–4 days £1,400–£2,800
Wet rot localised — joist end repair 1–2 affected joist ends 1 day £280–£550
Wet rot localised — sole plate replace 2–6m of plate 1–2 days £450–£1,200
Wet rot under bath / WC hidden area exposed 1–2 days £450–£950
Dry rot small outbreak (1–2m² spread) localised eradication 2–4 days £1,400–£2,800
Dry rot medium outbreak (3–6m² spread) partial wall opening 5–10 days £3,200–£6,000
Dry rot large outbreak (multi-room) major eradication 2–6 weeks £6,000–£18,000
Diagnostic survey (CSRT, written report) inspection visit 2–4 hours on site £150–£320
Borescope inspection (concealed timbers) targeted concealed area 1–2 hours £85–£180
Timber moisture content monitoring per visit 30 min £55–£140

Detailed Guidance

Diagnosis — what's killing the wood

Before quoting, identify the species. The treatment, the cost, and the guarantee differ dramatically.

Common furniture beetle (Anobium punctatum) — the dominant UK woodworm. Active beetles emerge May–August. Round exit holes 1.5–2mm diameter. Frass (powdered wood + insect droppings) light cream colour, gritty texture. Affects sapwood of softwoods (pine, spruce) and hardwoods. Most common in roof timbers, floor joists, ground-floor sub-floor timbers. Treatable.

Death watch beetle (Xestobium rufovillosum) — period property pest. Round exit holes 3mm diameter. Frass coarser, bun-shaped pellets. Affects hardwood (oak, chestnut), particularly with fungal decay. Active spring. Treatable but harder — eradication usually needs surrounding moisture management.

House longhorn beetle (Hylotrupes bajulus) — confined to certain parts of South-East England (Surrey, Hampshire). Oval exit holes 6–10mm, frass coarse. Devastating to softwood roof timbers — can hollow rafters and joists almost entirely while leaving surface intact. Mandatory treatment in designated areas under historic Building Regulations Schedule 11. Notify local authority on identification.

Powder post beetles (Lyctus, Bostrychus species) — round exit holes 1–2mm, frass very fine like talcum powder. Affects hardwood sapwood (oak, ash, walnut). Imported in furniture and joinery. Less common in structural timber.

Wet rot (Coniophora puteana most commonly) — brown, cubical cracking pattern. Wood spongy, dark brown. Confined to area of moisture source. Mycelium pale yellow-brown, doesn't spread far from moisture source. Fix moisture, replace decayed timber, treat surrounding sound timber as a precaution.

Dry rot (Serpula lacrymans) — also brown cubical cracking, but with distinctive features: white-grey mycelium with watery droplets ("tears", hence "lacrymans"), red-brown fruiting bodies (sporophores), strands (rhizomorphs) up to 2mm thick that conduct water and nutrients across substantial distances including through masonry. Smells of mushroom or damp earth. Spreads aggressively. Requires major eradication, not localised repair.

Misdiagnosis costs — the biggest commercial risk

The two most expensive misdiagnosis errors:

  1. Treating "active" woodworm that's actually historic — old exit holes from a long-extinct infestation, with no live beetles or fresh frass. Spray treatment is unnecessary and the customer pays for a service that solves nothing. Detection: look for fresh frass beneath holes (light coloured, not sun-darkened); look for round, sharp-edged holes (active) vs weathered holes (historic); look for live beetles in May–August trapping.
  2. Treating wet rot when it's actually dry rot — localised replace-and-spray approach to dry rot leaves the rhizomorphs in the wall to recolonise. The 5-year guarantee fails when dry rot resurfaces 3–4 years later. Detection: look for white-grey mycelium with droplets, red-brown fruiting bodies, rhizomorphs visible at margins, mushroom smell.

Always inspect with the right tools: torch, knife (probe softness), moisture meter (measure timber MC), borescope (concealed areas), and time. A 90-second walk-through in a torchlit loft is not diagnosis.

Woodworm treatment — what's actually involved

For a confirmed active infestation:

  1. Identify treatable surface area — measure all accessible timber surfaces (joists, rafters, sole plates, sub-floor)
  2. Brush down loose surfaces — remove existing frass, dust, accumulated debris (also indicates fresh vs old frass)
  3. Apply treatment fluid by airless spray (Hudson sprayer, knapsack sprayer) at manufacturer-specified rate (typically 0.2–0.5 l/m² depending on product)
  4. Two coats for optimal penetration, allowed to dry between coats
  5. Inject high-risk areas (joist ends, sole plates) with cartridge gun where surface application alone won't penetrate
  6. Replace severely weakened timbers as carpentry sub-job (within scope or subcontracted)
  7. Issue written treatment record noting product used, area treated, application rate, date

Modern treatment fluids:

Solvent-based products with significant VOCs are increasingly being phased out under environmental regulation.

Wet rot — fix the cause first

Wet rot only occurs where timber moisture content exceeds 28% chronically. The treatment protocol:

  1. Identify and fix the moisture source — leaking gutter, defective render, plumbing leak, condensation, rising damp
  2. Open up the affected area — strip plaster, lift floorboards, expose substrate
  3. Allow timber to dry — natural drying may take weeks; force-dry with dehumidifiers if urgent
  4. Replace severely decayed timber (typically joist ends, sole plates, lintels)
  5. Treat surrounding sound timber with fungicide (boron-based) to prevent recurrence
  6. Replaster/refit to make good
  7. Issue 10–20 year insurance-backed guarantee

Localised wet rot scope (e.g. one joist end above a leaking shower) is £280–£780 fully fixed. Larger scope (sole plate failure across 3–4m of wall, multiple joist ends): £950–£2,400.

Dry rot — the major operation

Dry rot is the only timber problem that can spread through masonry to colonise distant timber. The eradication protocol (per BS EN 460 and PCA guidance):

  1. Trace the full extent of the outbreak — open up walls, ceilings, floors to find the boundaries of mycelium and rhizomorphs. This is often more invasive than the customer expects.
  2. Identify and eliminate the moisture source — without dryness, the rot returns
  3. Remove all infected timber PLUS 600mm beyond the visible end of decay
  4. Sterilise the surrounding masonry — biocide treatment (typically zinc-based) applied to walls within 1.5m of the outbreak
  5. Install a barrier — physical barrier or chemical barrier between treated area and any retained masonry
  6. Replace timber with treated softwood, often with end-grain dipping in fungicide
  7. Restore finishes — re-plaster, re-floor, re-decorate
  8. Issue 10–25 year insurance-backed guarantee

The cost variance is wide because the scope is unknown until opening up. A "small" outbreak that turns out to involve a chimney breast, sub-floor and ceiling void can quadruple in scope mid-job. Quotes for dry rot should always be on a "preliminary scope subject to opening-up findings" basis with daywork rates for unknown extras.

Insurance-backed guarantees — the customer's headline product

For both woodworm and rot work, the customer is primarily buying the guarantee, not the treatment. Insurance-backed guarantees (IBG) protect the customer if the installer goes out of business — without IBG, a 25-year guarantee is worthless if the installer ceases trading.

Major IBG providers:

Cost: £35–£140 per job to register, depending on scope and value. Always quote with IBG cost included — a "no IBG" quote is cheaper but customers know it's worth less at sale time.

Trade body — PCA and qualifications

The Property Care Association is the recognised trade body for damp, timber, and structural waterproofing. Qualifications:

PCA member businesses are subject to:

PCA membership costs £450–£1,800/year depending on business size. Member status is the quality signal customers (especially educated buyers, conveyancers, surveyors) look for.

COSHH and chemical safety

Treatment chemicals are classified as biocides under the Biocidal Products Regulations 2012. COSHH (Control of Substances Hazardous to Health Regulations 2002) requires:

For permethrin treatments, customers can typically re-enter treated rooms after 12–24 hours. Pets (especially fish, cats) are sensitive to permethrin and require longer exclusion. Always brief the customer in writing on re-occupation safety.

Frequently Asked Questions

How much does woodworm treatment cost in the UK 2026?

£450–£1,200 for a typical 30–50m² room or roof void treatment, £1,400–£2,800 for a whole-house spray. The fee includes a CSRT-qualified diagnostic survey, two-coat spray application of permethrin or boron-based treatment, written treatment record, and a 20–30 year insurance-backed guarantee. Severely weakened timber needs replacement at additional carpentry cost.

Can I tell if woodworm is active or historic?

Active infestation has fresh, light-cream frass beneath holes (look in spring/summer); sharp-edged round holes (not weathered); occasional live adult beetles emerging May–August. Historic infestation has dark, sun-aged exit holes; no fresh frass; weathered hole edges. A pencil dot test (mark a hole, return 6 months later — fresh frass appears at active holes) confirms activity over a season.

What's the difference between wet rot and dry rot?

Wet rot (Coniophora puteana most often) is confined to areas of chronic moisture above 28% — fix the moisture source and the rot stops, then localised replacement and treatment finishes the job. Dry rot (Serpula lacrymans) can spread through masonry via rhizomorphs to colonise distant timber. Identifiers: dry rot has white-grey mycelium with droplets, red-brown fruiting bodies, mushroom smell, and string-like rhizomorphs. Misdiagnosis is expensive — always get a CSRT-qualified surveyor for any rot you can't confidently identify.

Will the timber treatment guarantee transfer when I sell the property?

Yes if it's a properly insurance-backed guarantee from a PCA-member firm. The IBG transfers to subsequent owners during the guarantee period (20–30 years for woodworm, 10–25 years for rot). At sale, the customer provides the original guarantee certificate to the buyer's solicitor. A non-IBG installer guarantee may transfer in name only — without IBG backing, it's effectively worthless if the installer has ceased trading.

Do I need to treat woodworm if I've found old holes but no live beetles?

If there's no fresh frass and no live beetles emerging May–August, the infestation is historic and treatment is unnecessary. The damage already done won't worsen. Unless you have specific reason to suspect active infestation (warm humid loft conditions, recent emergence holes, etc.), spray treatment of a dormant historic infestation is over-treatment. A CSRT-qualified survey gives you a written assessment to rely on.

Regulations & Standards