Dry rot vs. wet rot: what is the difference?

Dry rot can be dangerous if left untreated. This article helps homeowners understand the difference between wet rot and dry rot, what causes it, how to treat it and what you can do to prevent it. 

In this situation, a single defect survey is required. Our surveyors in Kent, Thanet, Folkestone and property surveyors in London can help. Get in touch to get started.

Understanding wet rot, dry rot and woodworm

In March 2025, the Property Care Association (PCA) reported that weather patterns had provided the right environment for funguses that cause wet and dry rot to flourish. 

Whether it is timber joists within the roof structure, wooden panels or floorboards, all wood is at risk of decay. That might be through woodworm, or it could be caused by wet or dry rot. 

What is dry rot? 

Dry rot is an infection of wood by a single fungus called Serpula lacrymans.

Dry rot infestations start in damp and unventilated areas. However, it can occur anywhere within your property as it can spread without you even knowing. The fungus imports water from other areas using its long filaments (roots). These can even travel through damp walls and masonry to other parts of your property to find fresh wood. 

However for decay to start wood must be wet; it’s not just about damp air, which at an optimum temperature (around 22degC) will allow spores to survive. The spores need wet wood to actually grow. This is usually through severe water ingress, either rainwater leaks, faulty plumbing, flood, or long-term severe condensation. That said, dry rot is most likely in houses with poor ventilation and high humidity – so if there is constant condensation on windows, you should have this checked by a chartered surveyor.

Is dry rot dangerous?

It can be. Dry rot can affect the structure of your property if left untreated. 

It can also cause health issues if anyone in your property has an allergy to the spores, and people with asthma or eczema.

Do you have to declare dry rot when selling a house?

If you are aware of dry rot when you are selling a house, you must declare it to the buyer. That’s because it can cause structural defects. It is always our recommendation that you have a RICS Level 2 or RICS Level 3 survey when buying a new home, as we will see signs of damp and dry rot when we assess the property. 

What is wet rot?

Wet rot is caused by fungi called Coniophora puteana. It needs a much higher moisture content within the wood than dry rot (50% compared to 20% for dry rot). This is usually caused by water leaking from plumbing, guttering, stone pointing or downpipes.

Wet rot will grow and expand on an individual section of wet wood – it won’t spread in the same way as dry rot. However, it will weaken the timber if left untreated so needs to be treated. 

Wet rot might be found where there is proof damp proof coursing, rising damp or penetrating damp. 

Does wet rot spread?

No. Unlike dry rot, wet rot cannot spread from the affected area. It can only grow in wood that has a minimum of 30% moisture.

Dry rot versus wet rot – the key differences: 

Compare side-by-side—cause, spread rate, severity, and treatment.

Dry rot

Wet rot

Causes

 

 

 
  • A specific fungus called Serpula lacrymans that thrives on moisture
  • Properties with high humidity and poor ventilation
  • Either a tiny spore will invade the damp wood, or one of the filaments from an existing fruit will spread to damp wood – even through damp masonry
  • A group of fungus under two categories – brown and white. The most common ia Coniophora puteana 
  • Usually an unresolved water leak from either accidental flood or poor maintenance

Signs

 

 

 

 

 

 
  • Musty smell
  • Spongy timber
  • Brittle, crumbling timber
  • Deep cracks in timber
  • Patches of orange–brown spore dust either on the wood or even in the air
  • Grey strands on timber
  • Fruiting bodies that look like large mushrooms.(below is an example that has been left far too long)
  • Damp / musty smell
  • Cracking or distorted timber
  • Softened or spongy timber
  • Discoloured timber
  • Weakened timber
  • Black–brown mushroom like growths

 

Spread rate
  • Approx 3mm per day
  • It does not spread. It stays on the wet area of timber

Severity
  • If left untreated it can cause severe structural damage
  • Not as severe as wet rot but can still cause structural damage if left untreated

Treatment

 

 

 

 
  • Ensuring cause of moisture is resolved, 
  • Drying out the area
  • Plaster may need to be removed to see extent of damage
  • Fungicide can be used but most likely you will need to replace infected wood
  • Treating wood and plaster/masonry in nearby locations
  • Ensuring cause of the moisture is resolved,
  • Removing and replacing infected wood

Large patch of Serpula lacrymans fungus with white edges and brown spores growing on wooden wall and floor, causing dry rot—an issue often identified by damp surveyors.

How do you treat dry rot?

First you must identify the space where the dry rot started and where it may have spread to. Any affected wood will need to be replaced and surrounding, unaffected timber treated to prevent any further spread. The space must be ventilated and thoroughly dried out. 

The cause of the damp in the first place must also be resolved as a continued damp environment will allow the vicious cycle to start again. We recommend a chartered surveyor like us assess your property for damp and advise you on remediation. You should also use a specialist company for the dry rot.

White fungal growth on decaying wood, identified as Coniophora puteana—a fungus responsible for causing wet rot and often detected by damp survey specialists.

How do you treat wet rot?

Once you have identified that the cause of timber decay is wet rot, you should resolve the issue of the cause of the moisture and dry the space thoroughly. You will then need to replace any damaged timber. As with dry rot, having a specialist damp survey may help you to understand the cause of the issue and how to resolve it properly. Again, always use a specialist to resolve a wet rot issue.

How can I prevent dry rot?

Basic property maintenance and adequate ventilation will prevent dry rot. If you have had a sudden flood or other unexpected water leak, then ensuring it is dried out quickly is vital. 

How can I prevent wet rot?

Basic property maintenance and adequate ventilation will prevent wet rot. If you have had a sudden flood or other unexpected water leak, then ensuring it is dried out quickly is vital. 

How common is dry rot and wet rot?

There are no specific figures for properties with wet or dry rot. However, according to English Housing Survey 2023 to 2024: drivers and impacts of housing quality “1.3 million dwellings (5%) had damp problems present in one or more rooms”. So one can assume that each one of them is at risk of rot. We do know that wet rot is more common than dry rot, but dry rot is the most serious. It’s important to know the difference between the two as they have different treatments. 

How can Collier Stevens help with dry or wet rot?

If you suspect you have a problem with wet rot or dry rot, contact Collier Stevens. We can undertake a single defect survey and assess the areas you are concerned about. We will also be able to identify any other areas that may be at risk. We’ll then make recommendations for treatment and prevention. 

Get in touch via the form below or give us a call.

About the Author
Steve Way - Collier Stevens

Steven Way

Steven Way BSc MIHEEM MFPWS MRICS is the Practice Principal and is a Chartered Building Surveyor. With over 35 years as a practicing surveyor, Steve has a wealth of experience and expertise in both residential and commercial building surveying, party wall advice and disabled access auditing. He has also built his reputation as an expert witness.