Dry Rot


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Dry Rot

Dry rot decay is the gradual consumption of timber, plaster or other building material by the fungus Serpula lacrymans. It can occur in buildings of any age, given the right conditions and generally occurs in timber which has become damp and remained damp for an extended period of time.

Dry rot is the most serious form of timber decay in properties because of the speed at which it can destroy the wood or material that it affects and the range that it can spread to. Unlike other wood-destroying fungi, dry rot has a unique ability to transport water from a source, along its growth to its outer extremities where it is needed to feed the expansion of the fungus. Most wood-destroying fungi which do not share this characteristic are generally confined to the area of timber which is damp.  In addition, dry rot has a second characteristic which increases the range of its growth: it produces needle-like threads (referred to as hyphal threads), which can penetrate mortar and plaster,. These allow the fungus to affect large sections of walls in addition to timber. In doing so, dry rot can gradually move from room to room in a home, wreaking destruction as it goes.

Dry Rot decay affecting cellar joists

Dry Rot affecting joists in Leeds, Yorkshire

Dry Rot discolouring a timber floor in Wakefield, Yorkshire

Dry Rot discolouring a timber floor in Wakefield, Yorkshire

What causes Dry Rot?

Dry rot growth begins in timber which has become damp and remained damp for long enough to support the growth of the fungus. When undergoing dry rot treatment, 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 dry 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 Dry 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 Dry Rot:

Dry Rot causes the collapse of a timber floor

Dry Rot causing the collapsed of a floor in York

Dry Rot affects a Timber Floor in Wakefield

Dry Rot causing the breakage of timber flooring in Leeds

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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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Dry Rot Treatment

How does dry rot form?

To understand dry rot treatment, it is essential to understand how rot forms. Fungal timber decay generally starts in similar ways, irrespective of the kind of fungus, and this applies to dry 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.

Signs of Dry Rot

Dry 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 dry rot include:

  • Discoloured timber skirting boards, architraves or floorboards;
  • On floors which are covered, movement in the floor or bounce;
  • Discovery of fungus which is cotton wool-like or takes the appearance of any  of the outbreaks shown above; or
  • A red dust covering walls or floors.

Dry Rot Treatment

In any case, where dry 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. Where cutting out of the wood is undertaken, it is good practice to remove 600mm past the affected areas to ensure that all of the decay is removed. Any wall plaster which shows signs of decay should also be removed and the area treated with a suitable masonry biocide. In cases where it is not possible to treat the full extent of the outbreak on a wall (either because of the extent of the outbreak penetrating the wall or because the wall’s construction does not lend itself well to treatment), then a toxic barrier or irrigation of the wall may be preferable to starve the outbreak of a water supply. 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.

The above assumes that the cause of the damp which led to the dry 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 Dry Rot?”

ANSWER: We have listed some of the common signs of Dry Rot above on this page, but you should always seek an expert opinion due to the danger that Dry Rot can pose to you and anyone living in the property.

“Is Dry Rot dangerous?”

ANSWER: The fungus Dry 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 Dry 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.

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.