Wet Rot Treatment in North London
Wet rot is the commonest timber decay in British homes — softened, darkened wood wherever timber stays wet. It's serious, but contained: fix the moisture, repair the wood, done.
What is wet rot? Wet rot is timber decay caused by fungi — most commonly cellar fungus, Coniophora puteana — that consume wood kept persistently wet (typically above 30% moisture). Unlike dry rot it stays confined to the damp timber itself and cannot spread across masonry to dry areas. Affected wood darkens or bleaches, softens so a screwdriver sinks in, and cracks along the grain; classic sites are window sills, door frames, joist ends near leaks and subfloor timbers over damp ground. Treatment is localised: cure the moisture source, cut out or splice-repair decayed sections, and treat adjacent timber — typically £300–£2,500 in North London.
Understanding the problem
Wherever water repeatedly reaches wood, wet rot follows: sills under failed paint and putty, frame feet standing in splash zones, joist ends against a wall with a bridged DPC, floor plates over a damp cellar, bathroom floors under slow tray leaks. The decay advances only as far as the wetness does — which makes wet rot fundamentally a moisture-diagnosis problem with a carpentry solution.
The risk is quiet progression in concealed places: a joist end can lose most of its bearing strength before a floor feels springy. That's why damp surveys probe timber and why persistent damp anywhere near wood deserves a look below the surface.
Signs and symptoms
- Timber that's soft and spongy under a probe or screwdriver
- Darkened (or sometimes bleached) discolouration of wood
- Cracking along the grain; surface skins over decayed interiors
- Flaking, blistered paint on sills and frames hiding soft wood
- Springy or bouncy floors near damp walls
- Localised damp, earthy smell under floors or in cupboards
Common causes
- Failed paint/putty letting water into sills and frames
- Leaking gutters and downpipes soaking adjacent timber
- Plumbing and shower leaks wetting floors and joists
- Bridged or failed DPCs keeping wall-adjacent timber damp
- Poor subfloor ventilation over damp ground
- Condensation persistently wetting concealed timber
Getting the diagnosis right
The timber survey probes suspect areas (decay hides behind sound-looking surfaces), moisture-maps the surrounding fabric to find the water path, and confirms the decay type — distinguishing wet rot's confined pattern from dry rot's spreading one, which changes the scope entirely. Structural members get particular attention at bearings: the report states which timbers are repairable in place and which need replacement or splicing, plus the moisture repair required first.
Treatment
- Fix the water — gutter, seal, plumbing or damp repairs (see penetrating damp and rising damp) so the timber can dry and stay dry.
- Repair the timber — decayed sections cut out; joinery splice-repaired or resin-repaired where appropriate; structural members replaced or spliced with pre-treated timber, isolated from damp masonry.
- Preserve — adjacent retained timber treated with preservative as a safeguard while residual moisture clears.
- Ventilate — where subfloor damp contributed, airbrick and subfloor ventilation works stop recurrence.
- Redecorate properly — sound painting and sealing of external joinery is the cheap ongoing defence.
What does it cost in North London?
| Item | Indicative range |
|---|---|
| Timber & damp survey | £320 – £450 |
| Sill/frame splice repairs | £150 – £600 per item |
| Localised structural repair (joist ends etc.) | £300 – £1,200 |
| Multi-area treatment & repair | £1,000 – £2,500 |
| Moisture-source repair | per defect (see relevant service) |
Wet rot caught early is a joinery repair; caught late it's structural work. The gap between those bills funds a lot of gutter maintenance. Figures are indicative for North London (2026) and vary with property, access and scope — written quotations follow a survey. See the North London Damp Cost Guide or try the Timber Treatment Cost Estimator.
Our process
Tell us the problem
Call or use the contact form — describe what you're seeing and where. Photos help.
Survey & diagnosis
An independent qualified surveyor inspects the property and identifies the true cause, with a written report.
Clear written quote
You receive a costed scope for exactly what the property needs — no more, no less.
Treatment & verification
Works are carried out by vetted independent specialists, with guarantees where applicable and verification that the fix worked.
Frequently asked questions
It's serious where it affects structural timber, but it's contained: it cannot spread beyond the wet area or travel through masonry as dry rot does, so treatment scopes are smaller and costs lower. The urgency is stopping the water and checking bearings.
Often, yes: where decay is partial, splice and resin repairs restore joinery, and preservative treatment protects the remainder — provided the moisture source is fixed. Timber decayed through its structural section needs replacement; the survey distinguishes the two.
Indicatively £150–£600 per repaired sill or frame, £300–£1,200 for localised structural repairs like joist ends, and £1,000–£2,500 for multi-area work — plus the moisture repair itself. Survey first (£320–£450) to establish extent.
It advances wherever the wetness persists — deeper into the same timber and along the wet zone. It won't jump to dry areas, but the affected members keep weakening, and persistent damp can eventually invite dry rot, which does spread. Neither improves with time.
Keep water off wood: maintain paint and seals on external joinery, keep gutters clear, fix leaks promptly, and preserve subfloor airflow. Wet rot has no persistence trick — dry timber is immune.
Worried about damp, mould or a wet basement?
Speak to us today or book a survey — we'll arrange the right independent specialist for your property.