What Is Dry Rot?

Dry rot is a common problem in many homes and buildings. It is a type of fungal decay that can consume timber and affect plaster, and other building materials. The fungus responsible for dry rot is called Serpula lacrymans, it thrives in damp and humid conditions and causes dry rot when left untreated for extended periods of time.

Dry rot can be such a serious issue because of its speed and range of destruction. Unlike other wood-destroying fungi, dry rot has the ability to transport water from a source to its outer extremities, allowing it to feed and expand quickly. It also produces hyphal threads that can penetrate mortar and plaster, which means it can affect large sections of walls and easily move from room to room.

Dry rot can occur in buildings of any age, generally affecting timber that has been damp for an extended period of time, often due to poor ventilation, leaks, rising damp and penetrating damp.

Untreated dry rot can weaken the structural integrity of a building, causing significant and expensive damage. If you believe your property has dry rot it’s important to address the issue immediately.

Does your property have Dry Rot?

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.

Some common causes of dry rot include:

Water leaks
Leaks from roofs, gutters, or plumbing can cause water to penetrate the structure of a building and come into contact with timber.

Poor ventilation
Poor ventilation can cause moisture to become trapped in enclosed spaces, leading to dampness and creating a favourable environment for dry rot to grow and thrive.

Condensation occurs when warm, moist air comes into contact with cold surfaces and creates water droplets. This can happen in poorly ventilated spaces such as basements or cellars.

Bridged damp proof course
A bridged damp proof course can cause moisture to travel up the walls of a building, leading to dampness and creating ideal conditions for dry rot to grow.

What Causes Dry Rot?

High humidity
High humidity levels can cause moisture to build up in the air, which can then settle on timber surfaces and create conditions for dry rot to develop.

Poor building maintenance
Poor building maintenance can lead to the accumulation of moisture and dampness in a building, providing ideal conditions for dry rot to grow.

Rising damp
Rising damp occurs when groundwater rises up through porous building materials, such as brick, stone or concrete, and into timber. This can happen when the damp proof course is damaged or non-existent and is a particular issue in Yorkshire due to the high amounts of rainfall that the region experiences.

Penetrating damp
Penetrating damp occurs when water penetrates the external walls of a building often due to defects in the structure, such as cracked rendering or missing roof tiles. This can lead to dampness in internal walls and create conditions for dry rot to grow. Penetrating damp is a common issue for Yorkshire homes.

What are the Consequences of Dry Rot?

Dry rot can cause significant damage to the structural integrity of a building if left untreated. The impact of dry rot can be extremely costly to repair if left for too long and can become a major safety issue. The below are some of the most common consequences of dry rot:

Reduced structural integrity
Dry rot fungus breaks down the fibres in timber, causing it to lose strength and become brittle. Over extended periods of time, this can cause timber to lose its load-bearing strength, which will lead to sagging and collapsing of floors and ceilings. Eventually this will cause a building to become unsafe and even uninhabitable.

Damage to walls and ceilings
Dry rot will often spread to other parts of a building, including masonry, plaster, and between rooms. This will cause cracking, flaking, and peeling of paint, wallpaper, or plaster. If unidentified and untreated, the dry rot fungus can continue to grow and spread, causing even further damage to your building.

Health hazards
Aside from structural health hazards, the presence of dry rot indicates that the property suffers from damp, which can be hazardous to health. Damp conditions in the home can be particularly dangerous for the elderly, children and people with existing respiratory conditions such as asthma or allergies. Prolonged exposure to these conditions can cause coughing, difficulty breathing, and chest tightness.

Decreased property value
If left untreated, dry rot can significantly decrease the value of a property. Dry rot will be flagged in property surveys and inspections, putting of perspective buyers. The effects of dry rot can also cause a building to look dilapidated and unattractive, making it more difficult to sell or rent.

What are the Signs of Dry Rot?

Dry rot is a serious maintenance issue that can cause significant and widespread damage to any property if left untreated. It’s important to be able to recognise the key signs of dry rot to prevent further damage and maintain the structural integrity of your building.

But, remember that these signs may not always indicate dry rot, and that a professional inspection is the only way to know for certain if dry rot has affected your building.

Some key signs of dry rot are:

  • Discoloured and darkened timber, including skirting boards, architraves, or floorboards
  • Cracks and cuboidal fractures in the timber, often accompanied by a deepening of the splits over time
  • Wood that feels dry and crumbly to the touch
  • The presence of a distinctive mushroom-like smell
  • The appearance of a white or grey cotton wool-like growth on the surface of the timber
  • The development of deep, wide cracks in the timber, often accompanied by a shrinking and cracking of the surrounding plasterwork
  • A distinctive orange or rust-coloured dust, caused by the spores of the dry rot fungus
  • A hollow sound when tapping the timber, indicating that it has lost its structural integrity
  • The presence of ‘fruiting bodies’, which are usually brick-red in colour and shaped like pancakes, often found growing on the surface of the timber or in damp, dark places nearby.

Yellow dry rot developed on a wall

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. When cutting away affected wood, it’s good practice to remove at least 600mm past the affected area(s) to ensure that all the decay is removed.

Any wall plaster which shows signs of decay should also be removed. 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. Once this is done, we use the ALLDAMP Dry Rot Solution to treat the affected areas which will kill any remaining dry rot fungus. Additionally, use of this Solution, prevents any future spread of the decay. 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, or find out more about dry rot in Huddersfield.


How can I tell whether a fungus is Dry Rot?

We have listed some common signs of Dry Rot above on this page, but one of the easiest ways to identify dry rot is the condition of timber. Timber affected by dry rot will often split and develop a grey/white layer. 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?

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?

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 ALLDAMP Dry Rot Solution.

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