Wet Rot


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Wet Rot

Wet rot decay is caused primarily by the fungus Coniophora puteana and it occurs in timber which has become damp and remained damp for some time. Growth starts in wood which has a persistent moisture content of above 20%. The fungus forms fruiting bodies, which disperse clouds of spores. These are carried by natural air currents within a home, allowing wet rot to spread to other areas where it can grow. The spores which land on suitably damp and untreated timber germinate by pushing hollow threads into the timber which are called hypha. The hypha branch out deeper into the wood through smaller needle-like tubes called mycellium. The mycellium consumes and breaks-down the damp timber into food to sustain the growth of the wet rot.


Damp timber can also come under simultaneous attack from woodworm, which need similar conditions to thrive as those of wet rot. Some woodworm, such as weevil, only attack decaying wood. When timber is affected by both wet rot and woodworm, the strength of the timber deteriorates rapidly, which can take a considerable toll on the structural integrity of the property.


Unlike dry rot, wet rot cannot expand onto and through masonry, meaning that it generally remains confined to the area in which it started. However, if damp is affecting a large area of timber, it is highly possible that rot will spread a considerable distance.

Wet Rot affecting flooring joists

Wet affecting floorboards in York, Yorkshire

Cellar joists affected by Wet Rot decay in Yorkhire

Wet Rot and Weevil destroying timber flooring in Selby

What causes wet rot?

Growth begins in timber which has become damp and remained damp for long enough to support the growth of the fungus. When addressing a rot problem, the source of the damp which has affected the timber must first be identified and resolved. The following is a list of sources of damp which can lead to wet rot decay:

Roof defects

The integrity of the roof should be inspected to check for any defects which might cause water to leak into the building, such as blocked guttering, defective surfacing to valley gutters, missing or broken tiles and faulty flashing around chimneys.

Wall defects

The condition of external walls is perhaps the most obvious factor to check when determining whether damp will affect a property. A properly constructed and maintained wall will repel water and allow a degree of ventilation to prevent humidity building inside the property or beneath floors. Factors which can inhibit a wall’s efficacy at doing this include the deterioration of mortar in brickwork joints, a faulty or missing damp proof course, the bridging of the damp proof course, blocked or missing air bricks, cracked or broken internal pipework, faulty window flashing, continuous overflow from cisterns or water tanks.

Internal defects

A range of internal conditions can cause the source of the dampness which leads to Wet Rot. A solid floor without an effective damp proof membrane will allow water to rise through it and into any adjacent timbers such as skirting boards, condensation/ water vapour which comes into contact with timber, the trapping of flood water beneath a timber floor, leaking internal pipes or toilets and linoleum tightly fitted over non-ventilated or poorly-ventilated timber floors will trap water vapour and dampen the timber.

Consequences of wet rot:

Decayed floor collapses in Wakefield

Wet Rot causing the collapsed of a floor in Wakefield

Wet Rot decay causes total collapse of floor in York

Wet Rot causes the complete collapse of a floor in York

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Our accreditations

Below, you’ll find the logos of the organisations with which we are accredited.  Click on them to find out more information.

The logo of the Property Care Association PCA

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Trustmark logo, a UK Government Scheme


How does wet rot form?

To undergo treatment, it’s important to understand how wet rot forms. Timber decay through fungus generally starts in the same way, regardless of the kind of fungus it leads to. The sporocarp of a fungus, the part that reproduces or ‘fruits’, sets in the affected area of the timber. Here it produces millions of spores which lead to the expansion of the affected area and these then increase the rate of timber decay. As the spores spread out, they land on nearby wood and timber. Here they form a collection of feeding branches called mycelium. The mycelium begins to break down the timber, using it as food for the fungus. When this occurs, the appearance of timber begins to change. It may appear bleached or discoloured, for example. Eventually, without treatment, the wood will rot to the extent that it becomes unsafe. It can lead to damage to a property’s structural support, for example, and cause the structure to collapse. Wooden floors can become unsafe to walk on and occupants can no longer live in the property.

Signs of Wet Rot

Wet rot is a progressive and aggressive maintenance issue. Untreated, it can cause significant and widespread damage to any home which is why it’s essential to act fast whenever you suspect a problem. Signs of wet rot include:

  • Discoloured and darkened timber skirting boards, architraves or floorboards;
  • On floors which are covered, movement in the floor or bounce;
  • Discovery of fungus which is skin-like in appearance and yellow or dark brown; or
  • A stringy fungus which bleaches the wood which it affects.

Wet Rot Treatment

Where wet rot is discovered, the badly decayed wood which is beyond repair should be removed and disposed of as a first action, no matter where the rot is found. This is the first step in wet rot treatment. Allerton Damp Proofing then use a fungicidal solution to reduce and stop the spread of the further rot due to the already infected timber. Any wood which is not removed needs to be treated with a suitable timber preservative and any timber used to replace the old should be pre-treated against fungal decay. This makes sure that the fungus does not return.

The above, however, does assume that the cause of the wet rot – the damp – has been solved. For more information about damp treatment, visit our damp proofing page.


“How can I tell whether a fungus is Wet Rot?”

ANSWER: We have listed some of the common signs of Wet Rot above on this page, but you should always seek an expert opinion due to danger that Wet Rot can post to you and anyone living in the property and we would advise undergoing wet rot treatment.

“Is Wet Rot dangerous?”

ANSWER: The fungus that causes wet rot is not directly dangerous to our bodies or our health. However, the damage it causes to timber is a risk and makes it a considerable danger in the home. It’s not uncommon for wet rot to cause considerable damage to floors or the structure of a building.

“Does timber affected by rot always need to be replaced?”

ANSWER: No, not always, but it depends on the extent of the outbreak and how long the timber has been affected by it. As time passes, more and more of the timber is consumed by the rot, making it weaker; if the timber has become too weak to bear weight, it should be replaced. Our surveyors assess the extent of any outbreak and try to keep the replacements to a minimum to save on cost. If timber does not need to be replaced, our staff will treat it with a specialist fungicide instead.

Please note that, as a provider of essential services, we are still open for business, with some restrictions. As a new or existing customer, you can continue to call us to discuss new or existing projects.

Please note that we have had to restrict our work in occupied homes considerably, due to the risk that this might pose to our customers and workforce. However, our work in empty homes and properties continues largely as normal.

If you would like to speak to a member of our team about anything to do with our work during the COVID-19 crisis, please contact us, as normal, using any of the contact details on this site.