Dry Rot vs Wet Rot: Treatment Costs and Signs

Timber rot is one of the most destructive problems in UK homes - and one of the most misunderstood. The difference between dry rot and wet rot isn't academic: dry rot is a far more serious condition that can spread through masonry and destroy structural timbers throughout a building, while wet rot stays localised near the moisture source.

Getting the diagnosis right determines whether you're facing a £500 repair or a £15,000 remediation.

Dry Rot vs Wet Rot: The Key Differences

Critical distinction: Dry rot can travel metres through masonry in search of new timber, meaning the visible damage may be only a fraction of the total infestation. This is why specialist survey and treatment is essential.

Signs of Rot in Your Home

Where to Look

• Floor joists near external walls (especially ground floor)
• Window frames and sills - the most common location for wet rot
• Skirting boards at ground level, particularly on damp walls
• Under baths and showers where water may have leaked
• Loft timbers where roof leaks have gone unnoticed
• Sub-floor voids in houses with suspended timber ground floors
• Behind plaster on damp walls - rot can be hidden for years

Warning Signs

Visual:

• Timber that has darkened, softened, or is cracking
• White cotton-wool-like growth on timber or masonry (dry rot)
• Rust-red dust on surfaces (dry rot spores)
• Fungal fruiting bodies (mushroom-like growths) on timber or walls
• Crumbling or powdery timber when probed with a screwdriver

Physical:

• Springy or bouncy floors (joists weakened by rot)
• Skirting boards that come away easily from the wall
• A screwdriver pushes easily into timber (should resist)
• Doors or windows that stick (frames swelling or distorting)

Smell:

• A persistent musty, damp, or mushroom-like smell - especially in enclosed spaces

If you spot any of these, get a professional survey before the damage spreads.

Treatment: Wet Rot

Wet rot treatment is relatively straightforward because the fungus doesn't spread beyond the moisture source.

Step 1: Find and Fix the Moisture Source

This is the most important step. Without eliminating the moisture, treatment is pointless. Common sources:

• Leaking gutters or downpipes
• Failed window seals or putty
• Penetrating damp through walls
• Leaking pipes (especially hidden pipes in walls or under floors)
• Poor ventilation under suspended floors (blocked air bricks)
• Condensation in poorly ventilated spaces

Step 2: Remove Damaged Timber

Cut out and replace all timber that has lost structural integrity. Sound timber adjacent to the rot can usually be treated in situ with a fungicidal preservative.

Step 3: Treat Surrounding Timber

Apply a boron-based wood preservative to all timber within 600mm of the affected area to prevent future fungal growth.

Wet Rot Repair Costs

Treatment: Dry Rot

Dry rot treatment is more complex and expensive because the fungus spreads through masonry and behind surfaces.

Step 1: Specialist Survey

A PCA (Property Care Association) specialist surveys the full extent of the outbreak. This involves:

• Opening up walls, floors, and ceilings to trace mycelium strands
• Probing all timber within the affected area
• Mapping the fungus spread through masonry
• Identifying the original moisture source

Cost: £200–£500 for a dry rot survey.

Step 2: Eliminate the Moisture Source

As with wet rot, but even more critical. The moisture source that triggered the outbreak must be permanently resolved.

Step 3: Remove Affected Timber

All timber showing signs of dry rot is removed, plus an additional 600mm of apparently sound timber beyond the last visible sign of the fungus. This safety margin is essential because dry rot strands may have penetrated further than is visible.

Step 4: Treat Masonry

All masonry within and around the affected area is treated with a specialist fungicidal masonry treatment - typically irrigated through drilled holes to penetrate the wall. This kills any fungal strands within the masonry that could re-infect new timber.

Step 5: Environmental Controls

The treated area must be well-ventilated and allowed to dry thoroughly before new timber is installed. Replacement timbers are pre-treated with preservative, and new timber-to-masonry junctions use DPC material to prevent future moisture transfer.

Dry Rot Treatment Costs

Choosing a Specialist

For dry rot, always use a PCA-accredited contractor:

• PCA members must hold relevant qualifications (CSRT - Certificated Surveyor in Remedial Treatments)
• They provide insurance-backed guarantees (typically 20–30 years)
• Work is carried out to PCA Code of Practice standards
• The guarantee is transferable to future owners (important for resale)

Avoid general builders for dry rot work - the diagnosis and treatment require specialist knowledge. An incorrect treatment allows the fungus to regrow, and you'll pay twice.

Get at least 2–3 quotes. A reputable specialist provides a detailed survey report before quoting, explaining exactly what they've found and what treatment they recommend.

For wet rot, a general builder with experience can handle straightforward repairs (window frames, skirting boards). For structural timber replacement, use a specialist or ensure your builder consults with a structural engineer.

Prevention

All rot requires moisture. Prevent it by maintaining your home's weatherproofing:

• Clear gutters twice a year and fix leaks promptly
• Maintain pointing - repoint cracked mortar before rain penetrates
• Keep air bricks clear - never block sub-floor ventilation. The Energy Saving Trust advises maintaining ventilation even when insulating
• Fix roof leaks immediately - even small leaks cause rot over time
• Ventilate bathrooms and kitchens - use extractor fans to prevent condensation and mould
• Check window frames annually - scrape, prime, and repaint any areas where paint has failed
• Monitor for damp - damp walls are a precursor to rot

Rot and Property Transactions

Selling a Property with Rot

• Rot found during a buyer's survey is a major red flag and typically leads to 10–20% price renegotiation
• Get a specialist treatment with a transferable guarantee before marketing - this reassures buyers and protects the sale price
• Disclose any known rot history on the TA6 property information form

Buying a Property with Rot

• Any surveyor finding rot will recommend a specialist investigation
• Get a full dry rot survey (£200–£500) before committing
• Use the treatment cost as a negotiating tool - see our guide to builder quotes for negotiation tips
• Ensure any existing guarantees from previous treatment are transferable

Next Steps

1. Identify the type - use the comparison table above to distinguish dry from wet rot
2. Find the moisture source - rot is always a symptom of a wider damp problem
3. Get a specialist survey for any suspected dry rot - find a PCA member
4. Get a repair estimate - use our repair calculator for initial costs
5. Fix the moisture source first - treatment without fixing the cause is wasted money
6. Check our glossary for terms like mycelium, fruiting body, DPC, and sub-floor ventilation