Dry rot ( Serpula lacrymans ) is one of the most serious threats to UK homes. Unlike wet rot, dry rot has the unique ability to spread through masonry and plast...
Dry rot (Serpula lacrymans) is one of the most serious threats to UK homes. Unlike wet rot, dry rot has the unique ability to spread through masonry and plaster to find new timber, meaning a small outbreak can quickly compromise the structural integrity of your entire property.
For UK homeowners, identifying and treating dry rot early is essential to avoid spiralling repair costs. This guide covers the essential steps, realistic costs for 2025/26, and how to ensure the fungus is eradicated for good.
What Does the Work Involve?
Dry rot treatment is a multi-stage process that focuses on both killing the fungus and removing the moisture source that allowed it to grow. A professional damp proofer or timber specialist will typically follow these steps:
- Moisture Identification: Locating and fixing the source of water, such as a leaking pipe, blocked gutter, or rising damp.
- Exposure: Removing plaster, skirting boards, and flooring to find the full extent of the mycelium (fungal strands).
- The "One Metre Rule": Removing all affected timber plus an additional metre of "clean" wood beyond the last visible sign of decay to ensure no microscopic spores remain.
- Sterilisation: Applying high-strength fungicidal "biocides" to the remaining timbers and "masonry sterilisation" to the surrounding brickwork.
- Structural Reinstatement: Replacing removed timbers with pre-treated wood and installing new plasterboard or lime plaster.
- Ventilation Improvements: Installing air bricks or vents to ensure the area remains dry and prevents future outbreaks.
Typical Costs
The cost of dry rot treatment varies significantly based on how far the fungus has spread through the walls and floors. Simple surface treatments are rare; most jobs involve significant "strip-out" and reconstruction work.
| Item | Low £ | High £ | Notes |
|---|---|---|---|
| Specialist Timber Survey | £150 | £350 | Often refundable if you book the work. |
| Minor Localised Treatment | £600 | £1,200 | Small area of floorboards or skirting. |
| Structural Floor Repair | £2,000 | £4,500 | Replacing joists and floorboards in one room. |
| Extensive Multi-Room Work | £5,000 | £15,000+ | Large-scale structural timber replacement. |
| Fungicidal Masonry Injection | £30 | £60 | Per linear metre of wall treated. |
What affects the price? The primary cost drivers are the extent of the structural damage and the accessibility of the timber. If joists are embedded in thick stone walls or located under expensive kitchen fitting, the labour costs for "opening up" the area will increase significantly.
How Long Does It Take?
The duration of the project depends on the drying-out period required and the scale of the timber replacement.
- Initial Survey: 1–3 hours depending on property size.
- Small Localised Repair: 2–3 days (including strip-out and treatment).
- Major Structural Work: 1–3 weeks, depending on the number of joists and floor area.
- Drying Out Period: Several weeks or months may be needed before final redecoration can occur.
DIY or Professional?
Dry rot is not a DIY job. While you can buy fungicidal sprays at hardware stores, they rarely penetrate deep enough into the wood or masonry to kill the root of the infection.
Failure to eradicate every trace of dry rot often leads to a "rebound" infection within 12–18 months. Professionals use industrial-grade chemicals and provide insurance-backed guarantees that are essential when you eventually come to sell your home. Furthermore, if structural joists are affected, a professional must ensure the replacements meet UK Building Regulations.
Choosing the Right Tradesperson
Not all builders are timber specialists. It is vital to hire someone who understands the specific biology of Serpula lacrymans.
- Check Qualifications: Look for surveyors with the CSRT (Certificated Surveyor in Remedial Treatments) or CSTDB qualification.
- Trade Bodies: Ideally, the firm should be a member of the PCA (Property Care Association).
- Insurance-Backed Guarantees (IBGs): Ensure they offer a 10–20 year guarantee that remains valid even if the company stops trading.
- Red Flags: Be wary of anyone who suggests "just painting over it" or fails to look for the source of the moisture.
Top Question: Ask your tradesperson: "Will you be treating the masonry as well as the timber?" If the answer is no, they are not treating dry rot correctly.
UK Regulations
Dry rot treatments must comply with several UK standards to ensure safety and structural integrity.
- Part A (Structure): If you are replacing structural floor joists or roof timbers, the new wood must meet specific grade requirements (usually C24) to ensure the house remains safe.
- COSHH: The chemicals used for fungal treatment are hazardous. Your contractor must provide a COSHH assessment and ensure the property is safe for re-entry.
- Health and Safety: Proper PPE and ventilation are required during the removal of spore-heavy dust and the application of biocides.
Common Problems
- Misdiagnosis: Mistaking dry rot for wet rot. Wet rot stays localised, but dry rot travels; treating dry rot with wet rot methods will result in failure.
- Ignoring the Source: Treating the fungus without fixing the leak or ventilation issue. If the timber stays damp, the rot will return.
- Inadequate Strip-Back: Not removing enough "healthy looking" timber. Microscopic hyphae can live inside wood that looks fine to the naked eye.
- Poor Ventilation: Blocking up air bricks during the repair process, which traps moisture and creates a "hot house" for new fungal growth.
Frequently Asked Questions
Is dry rot covered by standard UK home insurance?
Usually, no. Most UK insurers view dry rot as a "gradual operating cause" or a maintenance issue rather than "sudden accidental damage." However, if the rot was caused by a sudden burst pipe, you may be able to claim for the plumbing repair, though rarely the rot treatment itself.
What is the main difference between wet rot and dry rot?
Wet rot needs a very high moisture content (around 50%) and stays in the damp area. Dry rot can survive at lower moisture levels (around 20%) and can grow through bricks and mortar to find dry wood in other parts of the house.
Can dry rot affect my health?
While dry rot itself isn't toxic like some black moulds, the damp conditions that cause it can lead to respiratory issues. The massive release of spores during an outbreak can also aggravate asthma or allergies.
How can I tell if I have dry rot?
Look for a distinct "mushroomy" or earthy smell, deep cracks across the grain of the wood (cuboidal cracking), and grey, skin-like strands on masonry. In advanced stages, you may see a "fruiting body" that looks like a fleshy, orange pancake.
Can I sell a house that has had dry rot?
Yes, provided you have a completion certificate and an insurance-backed guarantee from a reputable PCA-registered firm. Without this paperwork, buyers may struggle to get a mortgage, and the property value could be significantly affected.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
