Dry Rot, Identification, Treatment and What It Means for a Sale

What is Dry Rot?

Dry rot is caused by the fungus Serpula lacrymans. It is the most destructive form of timber decay found in UK buildings and can spread through masonry as well as timber, making it uniquely dangerous compared with other forms of fungal decay. Despite its name, dry rot requires moisture to become established, typically a timber moisture content above 20%, but once established it can spread into comparatively dry areas.

The Property Care Association (PCA) is the authoritative body on fungal timber decay in the UK, and its guidance forms the basis of industry practice for survey and treatment.

How to Identify Dry Rot

Dry rot goes through several stages, each with recognisable characteristics:

The cuboidal cracking pattern, sometimes described as resembling crocodile skin, is one of the most reliable visual indicators of dry rot in timber.

How Dry Rot Spreads

Serpula lacrymans is unusual among timber-decaying fungi because its mycelial strands can penetrate and travel through masonry, plaster, and other inert materials to reach fresh, untreated timber. This means that an outbreak in one room can spread through a wall to adjacent rooms or floors without any visible timber connection.

This capacity to spread makes dry rot significantly more expensive to treat than wet rot. Treatment must address not only the visibly affected timber but also the surrounding masonry and structure.

Treatment, The PCA Approach

The PCA's recommended treatment protocol for dry rot involves:

• **Identifying and eliminating the moisture source**, this is essential; without removing the moisture ingress, treatment will fail
• **Removing all affected timber**, cutting back to sound wood at least 300–450mm beyond the last visible sign of infection
• **Treating surrounding masonry**, applying fungicidal solution to masonry in a defined zone around the outbreak
• **Replacing timber with pre-treated or naturally durable species**, new timber should be pre-treated with a preservative
• **Improving ventilation**, to prevent conditions that allowed dry rot to establish

A PCA-member contractor should provide a guarantee for treatment work, typically for a period of 20–30 years. Guarantees from PCA members can be assigned to new owners on a property sale.

Dry Rot and Property Transactions

The discovery of dry rot during a survey, or disclosure of previous dry rot treatment, raises several important considerations for buyers:

• **Cost:** Dry rot treatment is significantly more expensive than wet rot treatment due to the extent of masonry treatment required. Costs vary widely depending on the severity and location of the outbreak.
• **Guarantees:** If the seller has a PCA guarantee for previous treatment, request a copy and check whether it is assignable to you as the new owner.
• **Reinspection:** Even where treatment has been carried out, buyers should have the property reinspected by a PCA-member surveyor to confirm the treatment is holding and the moisture source has been permanently resolved.
• **Renegotiation:** A dry rot outbreak identified at survey is a legitimate basis for renegotiating the purchase price to reflect the cost of remediation.

Property Passport UK records publicly available data on property history that can provide useful context, but dry rot can only be identified through physical inspection by a qualified surveyor.