Dry Rot

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How to identify dry rot

Dry rot is an aggressive form of fungal growth that can cause serious timber decay and weaken structural timber in buildings. We have designed this guide to help you identify the early signs of dry rot, understand what causes it, and how to act quickly to repair any damage.

Thankfully, a dry rot treatment programme carried out by an experienced and qualified specialist can repair or replace affected damp timber and eliminate the problem. The earlier you can identify dry rot the simpler and more cost-effective solving it becomes. You can book a wood rot survey or learn more about dry rot treatment by clicking the button below.

Dry rot under floorboard

What is dry rot

Dry Rot (known by the scientific name of Serpula lacrymans) 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 with noticeable cracks running through it, making any affected surface in your home very vulnerable indeed.

In its search for timber to consume, dry rot spores, unlike wet rots, are even capable of spreading through thick walls and over surfaces like steel or brick to attack another source of wood. A mushroom-style fungus called a sporophore will often form, and these give off millions of spores in the form of red dust. This severity and ability to spread means it requires specialist action to avoid extensive damage.

Identifying dry rot

Identifying dry rot at an early stage is vital to minimising the amount of damage it can cause to your property and reducing the eventual repair bill. While our guide below will help you to understand and recognise what dry rot looks like, you should be aware that it is likely to be found in areas of the property where people do not often look such as under floorboards, behind plasterboard or up in attics.

To help you identify a potential problem in your home, the next section of our guide will describe the most common signs of rot alongside some pictures to help you know what the signs of dry rot look like and not to mistake it with wet rot or other damp issues

Signs of dry rot fungus

What are the signs of dry rot

If you notice any or all of the following signs of dry rot then we would strongly advise that you consult with a professional wood rot expert to determine the best way to proceed with eliminating any wood destroying fungus from your home.

You may be able to cross reference the problems in your property with some of the symptoms below, however it could be the case that these are just the visible signs, and you have a deeper outbreak in a hard to spot area of your home like behind plaster or in a basement or cellar.

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.

Damaged & discoloured timber

Timber affected by dry rot will often darken in colour and will become so dry and brittle it will break or crumble easily. Timber affected by dry rot will also have distinct “cuboidal cracking.”


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/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. It is likely to get a lot worse if mycelium growth can occur.

Mushroom style fungus

The last stage in the lifecycle is the most visually striking - the mushroom-like 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.

Does dry rot smell

The fungus is often accompanied by a smell which is a damp musty odour reminiscent of wet 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 to make people aware rot is present in their home.

What causes dry rot

Dry rot is caused when humidity (between 18 - 30%) and poor ventilation combine to provide the perfect damp habitat to allow fungus to grow. As such, rot is actually a type of damp problem and can attack any type of property with high moisture content, from the very old to the newly built if the following conditions are present:

  • Dry rot spores
  • Poor ventilation
  • Timber
  • Moisture
  • Oxygen

Dry rot spores are actually around us all the time and will be found in most houses without causing any problem. However, these spores can develop into fungal growth if they settle in a location with a food source (damp wood) and sufficient moisture to allow them to develop and germinate.

Once a dry rot infestation has taken hold in your property then you will have to take action to remove the fruiting body and ensure affected timbers are treated and replaced. Without an effective course of treatment, the dry rot will continue to spread and likely cause serious structural damage to your home.

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 wood rot infestation - even when the rot is in concealed areas of a property.

After a thorough rot survey, when our expert surveyor is satisfied they have identified the presence of dry or wet rot, then a bespoke dry rot treatment plan will be developed and presented to you. 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, meaning that you can enjoy complete peace of mind knowing that the fungal infestation has been completely removed and eradicated from your home.

Is it dry rot or wet rot

Trying to identify the difference between dry rot and wet rot can be difficult without industry training and experience.

They share many of the same characteristics and will both cause cracking to the timber, leave affected areas soft and spongy and can both result in mushroom-style fruiting bodies. In contrast, wet rot will only be present in the immediate area of a water source, as it requires a higher moisture content. Wet rot can usually be found by a leaking roof, pipes, window sills or appliances like washing machines.

An experienced wood rot surveyor would be able to identify if the fungus is indeed serpula lacrymans, or a type of wet rot, with the most common being Coniophora puteana, Poria vaillantii and Phellinus contigus. For this reason, we would always recommend that you ask a specialist to conduct a thorough dry rot survey for peace of mind.

Your local dry rot specialist team

At Peter Cox, we have been surveying and treating dry rot problems since 1951.

If you suspect your property has rot, then call the dry rot specialists at Peter Cox. Our specialists will identify any rot outbreak and other related damp issues. Alternatively use the contact button below to get the help and guidance you need from our experienced and qualified team at one of our many local branches across the UK.

Author: Steve Jameson CSRT CSSW

Steve is our National Operations Manager and has overseen countless dry rot treatments during his 30 years in the business. As one of the nation's most experienced professionals in the field of dry rot and timber decay, there are few people better placed to offer help and advice for your property.

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