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. Wet Rot growth starts in wood which has a persistent moisture content of above 20%. The fungus forms fruiting bodies, which disperse clouds of spores which are dispersed 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 an untreated timber germinate by pushing hollow threads into the timber which are called hypha. The hypha branch out deeper into the timber 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.

Alongside Wet Rot, damp timber can also come under simultaneous attack from Woodworm, which also need similar conditions to thrive as 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 Wet 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?

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 Wet 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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How does Wet Rot form?

To understand how to treat Wet Rot, it is essential to understand how it forms. Fungal timber decay generally starts in similar ways, irrespective of the kind of fungus, and this applies to Wet Rot. A fruiting body, or sporocarp of a fungus, forms in the affected area of the timber where it produces millions of spores; inevitably, this leads to the expansion of the affected area and thus increasing the extent of the timber decay. As the spores are dispersed, they land on nearby timber where they form mycelium (a collection of feeding branches). At this point, the mycelium begins to break down the timber which it uses as a form of food. When this occurs, the appearance of timber will change considerably and may appear bleached or discoloured. Eventually, if the spread of the fungus is left unchecked, the timber will decay to the extent that it becomes unsafe and dangerous to the inhabitants. Where such timber forms the structural supports of a property, its decay may lead to the collapse of the structure.

Wet Rot- When to act

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. Telltale 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.

Treating Wet Rot

In any case where Wet Rot is discovered, the badly decayed wood which is beyond repair should be removed and disposed of as a first action. The use of a fungicidal solution is necessary to prevent the spreading of the decay by the disturbance of the affected timber. Any timber which is not removed should be treated with a suitable timber preservative. Any timber used for replacements should be pre-treated against fungal decay to ensure that the fungus does not return.

The above assumes that the cause of the damp which led to the Wet Rot outbreak has been cured. For more information on our damp proofing services, 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.

“Is Wet Rot dangerous?”

ANSWER: The fungus Wet Rot is not directly dangerous to our health, but the damage that it can cause to timber makes it a considerable risk to have in your home. The collapse of floors and ceilings affected by Wet Rot is not uncommon.

“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.