Dry Rot

Home » Expert Guides » Timber Preservation Guides » Dry Rot Treatment Guide

What Is Dry Rot?

Dry rot, or Serpula Lacrymans, is a term used to describe a unique type of wood rot that occurs in damp timber despite its misleading name. Dry rot is the most serious form of fungal wood decay as it attacks the parts of timber that provide strength.  

All a dry rot attack takes is a small dry rot spore or cross-contamination from an already infected material. It is able to spread without any source of moisture as it generates its own moisture through digestion of the timber. 

Dry rot differs from wet rot as dry rot is capable of spreading far beyond an initial water source despite both requiring moisture to germinate. 

What Does Dry Rot Look Like

Due to the potential serious consequences of dry rot it is essential to identify it at its early stages to minimise damage to your property. An early sign of dry rot is an unpleasant and musty smell which may lead you on to looking for further signs, such as.

  • The first stages of dry rot can look like cotton wool and may have droplets of water if in a particularly humid area.
  • White with yellowing fungal growths.
  • Sunken wood anr any shrinkage.
  • Darkening cracks in wood.
  • Large flat mushroom shaped growths can grow on both infected wood and plaster / paintwork.

The different types of damp

There are essentially three types of damp a property can be affected by:

  1. Condensation
  2. Rising damp
  3. Penetrating damp

Rising damp and penetrating damp are caused by water ingress from outside of the property. Whereas, condensation is the result of high humidity in your home where hot, moist air makes contact with cold surfaces.

Condensation damp is usually more of a problem during winter when surfaces are colder giving humid air a place to condense. However, rising damp and penetrating damp are more likely to occur during wetter weather.

Stages of Dry Rot

There are 4 stages in the dry rot lifecycle and it may be useful to understand them to help diagnose if your problem is with dry rot.


At the beginning, dry rot starts as spores that are inactive until they make contact with timber and enough moisture to begin to germinate. Spores will usually become active when the moisture content is 20%.


Once the spores have found the ideal environment they will grow as hyphae and begin to break down the timber. These hyphae are identified by fine white tendrils that allow the fungus to penetrate and grow inside and outside the wood.


The hyphae grow and combine to become mycelium – a cotton wool-like fungal body that quickly spreads to new timber. This is the vegetative state and it is when the fungi spreads aggressively in search of timber.


The final stage is the fruiting body as it grows into a mushroom shaped body that produces dry rot spores. These spores are released from the surface and are transmitted through air currents to other parts of your property. This stage prolongs the life of the fungus as it essentially begins the lifecycle in another area that has the optimal conditions.

What causes dry rot?

Humidity arising through condensation, rising damp or penetrating damp that causes timbers to reach a moisture content of 20% or above. These conditions are perfect for the growth and spread of dry rot and it can affect all buildings from old to new. 

Dry rot spores will often be found all around us and in most buildings without causing any problems for the most part. Unless there is an underlying issue of damp which causes the right habitat for the spores to germinate most property owners will not have any issue. Diagnosing the underlying damp issue and correcting both the dry rot infestation and causes of damp is key to eradicating any dry rot attack.

The differences between dry rot and wet rot

This is a question that we get asked a lot when doing surveys and it is one we also have to ask ourselves when diagnosing a property’s timber decay issue. Both are wood destroying fungi, but they are both fundamentally different types of fungi. If you think you have seen signs of rot on timber in your home in Cambridgeshire we recommend you contact our team of professional experts to properly diagnose and treat any potential issue that can arise. 

Both types of rot can cause structural damage to your property, however, dry is the more serious concern as it can spread quicker and destroy more timber. Wet rot is the more common wood decay fungal growth but it is mainly constrained to areas of damp. One of the main differences between wet and dry rot is wet rot requires a moisture content of around 50% to grow, whereas dry rot can thrive in moisture content of just 20%.

Please read our quick wet rot guide if you think you have a wet rot issue.

Is dry rot dangerous?

Of the two timber fungi – wet and dry rot – dry rot is by far the most dangerous. It can not only compromise the structural integrity of a property, but the underlying issue of damp that causes rot can have a negative impact on your health.

Property damage through dry rot

Dry rot can aggressively attack timber in relatively low levels of moisture due to it being able to generate its own moisture. Dry rot can spread through damp brickwork and plaster which means it can spread through a building with ease. It is difficult to treat and can lead to complete timber and brickwork failure and collapsing.

is dry rot bad for your health?

There is no evidence that dry rot or its spores contain any toxic chemicals or compounds so it is not directly a risk to your health. However, dry rot and rot in general usually means that there is an underlying problem of damp in a building. Rising damp, penetrating damp and condensation in your home can elevate the risk of people who suffer from respiratory health problems. 

Can you prevent dry rot

Prevention is always better and cheaper than cure, so it makes sense to understand how you can prevent your property from dry rot. This generally means ensuring the building remains free of damp and dealing with damp if and when it occurs.

  • As dry rot is caused by a higher than usual moisture content it is important to thoroughly inspect your home, inside and out, to find where the damp is occurring. APP Protect are damp specialists and we provide honest damp surveys across Cambridgeshire to truly get to the bottom of any damp issue.
  • To prevent damp problems in your home it is wise to make sure your building has the required damp proof treatment.
  • If your property suffers from condensation then this could heighten the risk of dry rot germinating. If you think you may have a condensation problem then please have a read through our condensation guide.  

Dry Rot Treatment In Cambridgeshire

First off all a dry rot survey will need to be carried out by our highly experienced dry rot specialist team to make sure the issue is diagnosed correctly and the course of treatment is right. You will receive a full and detailed report that will outline all of the findings and the suggested ways to proceed so you are kept fully aware of what is happening.

A damp survey will also be completed to identify the source of moisture. This will detail what the damp problem is exactly and the best way to eradicate the damp and prevent it from recurring. 

We will need to have access to the infected wood so our technicians can carry out repairs or remove the infected wood completely.

This means removal of plaster work, floorboards, etc. to make sure we get to all of the infected areas. 

Replacing the damaged timbers and ensuring the affected area is structural sound again comes next.

The masonry and timber surrounding the affected area will need to have the required fungicidal treatment applied.

Reinstatement of the walls and ceilings that were removed in the process will finish the job.

We’re Ready To Help You

Please get in touch with our friendly team today and we can get the ball rolling on your project sooner than you think.

01223 244 515