Dry Rot

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What is dry rot?

Dry rot is an aggressive form of fungal growth also known as Serpula Lacrymans. It is a wood destroying fungi that feeds off the cellulose in timber in order to grow and spread. This process leaves timber in a dry and brittle state and can weaken structural timber in buildings as a result.

Keep reading this guide for expert help identifying the early signs of dry rot, understanding what causes it, and how to act quickly to repair any damage. The earlier you can identify dry rot the simpler and more cost-effective solving it becomes.
If you want to get our experts out as soon as possible, you can call us today or book a dry rot survey online by clicking the button below.

What causes dry rot

Dry rot is caused when a source of moisture and a lack of ventilation combine creating the perfect conditions for an infestation to start. There needs to be a source of food for the fungal spore - typically susceptible wood - and when the spore lands on the timber with moisture content over 20%, the germination process can begin before producing hyphae.

The spores themselves are very small, about 0.01mm, and almost invisible to the naked eye.

However large numbers of these spores will frequently collect around a fruiting body and form a reddish ‘dust’, which is a key sign to identify a significant attack of dry rot is present.

How does dry rot spread?

Dry rot has a few ways to spread throughout its fungal life cycle. For example, during its mycelium stage, dry rot can grow over and through various materials, including brickwork and masonry, in its search for more timber to consume.

If light activates the mycelium,a mushroom-style fruiting body called a sporophore develops. This releases spores that look like red dust. These spores drift on air currents and germinate on suitable surfaces. So the life cycle turns full circle.

All of this means dry rot can spread throughout a property fairly rapidly if the conditions are right.

You can find out more about the stages of dry rot below.

Identifying dry rot

Here are some ways to identify dry rot:

  • Timber shrinking and becoming darker
  • Cracks in a 'cuboidal manner forming.
  • A silky greyish coloured skin frequently tinged with patches of lilac/yellow colouration will form.
  • White fluffy cotton wool-like mycelium develops with strands that become brittle when dry.
  • Finally the most recognisable sign of dry rot is fruiting bodies, which have a soft fleshy pancake consistency the surface of which is orange or ochre-coloured.
  • Rust red coloured spore ‘dust’ can frequently be seen around fruiting bodies covering localised surfaces.

Identifying dry rot at an early stage can be key to minimising the amount of damage it will cause to your property and reducing the eventual repair bill. However, because dry rot can grow behind skirting or under floorboards, most people do not notice dry rot until it enters its later stages and starts to spread.

Signs of dry rot fungus

Stages of dry rot

The dry rot life cycle can be broken down into four main stages:

  • Spores
  • Hyphae
  • Mycelium
  • Fruiting body

You can cross reference any signs of rot  in your property with the extended descriptions of each stage below:

Rot spore dust

Spores are very common and usually harmless. However, if fungal spores start to appear in concentrated patches of rust coloured dust, this is a sure sign of an active problem.


Spores begin to produce hyphae when they come into contact with timber in damp and humid conditions. Hyphae are white/grey strands that look similar to spider silk.


Mycelium is a grey and white cotton-wool-like mass that dry rot produces when it spreads from timber it can no longer feed on. If you identify mycelium, it is vital that you treat the problem there and then. A dry rot problem is likely to get a lot worse if mycelium growth is allowed to spread.

Fruiting bodies

The last stage in the lifecycle is the most visually striking - the fruiting body. These fleshy masses of dry rot fungus look like large rust-coloured mushrooms. The fungus grows when it needs to pump fresh spores into the air to find more timber and start the cycle all over again.

What does dry rot smell like?

Dry rot fungus is often accompanied by a smell which is a damp musty odour reminiscent of mushrooms. Sometimes if the fungus has taken hold in a basement, under floorboards or behind a wall, then this pervading damp musty smell is the first sign that makes people aware that rot is present in their home.

The difference between dry rot or wet rot

Dry rot is a specific species of fungus (Serpula Lacrymans) whereas wet rot is a name given to a variety of fungi that requires timber with a far higher moisture content to grow (around 50%).

Wet rot usually affects timber at the source of the damp and will cease to grow when the source of moisture is taken away meaning it is often more localised.

Dry rot treatment

Using industry accredited training, years of on-the-job knowledge and specialist equipment, the experienced and qualified surveyors at Peter Cox can diagnose and treat any dry rot infestation.

After a thorough timber survey, our expert surveyor can devise a bespoke dry rot treatment laid out in a clear to understand report. If you choose to conduct the repairs with us then our trained technicians will get to work treating affected areas with our fungicidal spray and repairing or removing structural and decorative timbers.

Our treatment plans are covered by long lasting guarantees, if applicable. This means you can enjoy complete peace of mind knowing that the fungal infestation has been completely removed and eradicated from your home.

You can find out more on our specific dry rot treatment page.

Dry rot specialists

At Peter Cox, we have been surveying and treating property preservation problems since 1951. We have vast experience in dealing with fungal decay issues in homes, commercial premises and historical buildings. We are rated ‘Excellent’ on Trustpilot with over 2,000 independent customer reviews and are a Which? Trusted Trader. 

If you suspect your property has rot, then call the dry rot specialists at Peter Cox today to get the help and guidance you need.

Alternatively, use the contact button below to book a survey online.

Next Steps

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