Timber Decay from Rot

Fungal decay occurs in timber which becomes wet for a prolonged period and is the result of the attack by one of a number of wood-destroying fungi. Dry Rot and Wet Rot can affect buildings of all ages and if decay is discovered it should be identified and remedial action taken without delay. It is important to note that although Wet Rot and Dry Rot are both forms of fungal growth and share some characteristics, there are several crucial differences outlined below.  Finding the source of dampness and eliminating the ingress of moisture and promoting drying is always necessary as part of the treatment.

The main visual differences between Dry Rot and Wet Rot is the degree of development of mycelium on the wood surface and the ability of the fungus to spread into other timbers via adjacent masonry. It is important that the types of decay are distinguished since they require different treatment.

Our experienced and qualified surveyors endeavour to correctly identify the cause of and the type of fungal decay, the remedy and any associated building work required, all at the survey stage. This enables all trades to give more accurate estimates before any work is undertaken. Exposure work is rarely required at this initial stage.

Dry Rot

Dry rot is a more serious remedial problem which manifests in the form of an aggressive wood destroying fungal growth. In order to grow and spread, the fungus feeds off the cellulose in timber and can cause severe deterioration to any wood or timber it comes into contact with. Dry Rot generally only attacks damp timber.

Dry Rot, contrary to its name, requires some additional moisture, normally the timber is above 20% moisture content.

The fungal growth leaves the timber in a dry and brittle state with noticeable cuboidal cracks running through it, making any affected timbers in buildings vulnerable to structural decay. Dry Rot requires a source of moisture, however mycelium is capable of, and often spreads far beyond the initial water source. In its search for timber to consume, Dry Rot mycelium are capable of spreading through thick walls and over surfaces like steel or brick in order to attack another source of wood.

Dry Rot often leads to the appearance of a mushroom style body called a fruiting body, and these give off tens of thousands of spores in the form of rust coloured dust.

Dry Rot treatment carried out by an experienced and qualified expert can eliminate the problem and the earlier you can identify Dry Rot the more simple and cost effective treatment becomes.  The cause in the UK is normally associated with water ingress, often caused by postponed maintenance, faulty plumbing or Rising Damp.

Given the serious nature of Dry Rot problems, please see the identifying signs to look out for and help you act quickly to treat any problems.

Signs to identify Dry Rot


Musty unpleasant fungus like smell

Especially noticeable when carpets or floorboards are lifted.


Rusty coloured spore dust is very common and usually harmless

However, if Dry Rot spores start to appear in concentrated patches of rust coloured dust, this is a sure sign of an active Dry Rot problem and recent fruiting body.

Damaged Timber

Timber affected by Dry Rot will often darken in colour and will become so dry and brittle it will break or crumble easily. Rot affected timber will often have a distinct cuboidal cracking effect.


Dry Rot spores begin to produce mycelium when they come into contact with timber in damp and humid conditions

Mycelium are white/grey strands that look similar to thin flattened plant roots.

Mycelium can also be a grey/white furry mass that Dry Rot produces when it spreads from timber it can no longer feed from

Typically between floor joists with the appearance of white or yellow cotton wool like mass.


Mushroom like fruiting bodies are the last stage in the Dry Rot lifecycle and can be the most visually striking evidence

These fleshy masses look like large flattened rust-coloured mushrooms with a white flesh-like perimeter and they grow when dry rot needs to pump fresh spores into the air in an effort to find more timber

Wet Rot

Wet Rot is a generic name for timber decay as a result of fungal growth, caused by damp or wet conditions. While it is not as severe a problem as Dry Rot, it still has the potential to seriously impact the structural integrity of your property if left unremedied. There are a variety of different types of Wet Rot and it can grow anywhere in a building if conditions are right. In simple terms, Wet Rot is a form of fungal decay that is caused by the combination of water ingress and a lack of ventilation. Wet Rot occurs more frequently, but can be less serious than Dry Rot; decay is typically confined to the area where timber has become or remains wet.

Wet Rot requires a constant source of water to grow, thriving in conditions of 30-100% moisture. This is usually caused by poor maintenance such as defective plumbing/leaks, external guttering or Rising Damp.

Wet Rot typically cannot travel through masonry; mycelium does not typically spread into walls, and this can sometimes cause Wet Rot to go undetected for an extended period of time especially if in a non-visible area. Wet Rot is typically confined to the area of dampness.

Signs to identify Wet Rot

As explained, it is very important that the type and cause of the fungal decay are correctly identified before any corrective action can be considered. It is for these reasons that it is important that a detailed diagnostic inspection is carried out by our qualified surveyors.


Musty unpleasant fungus like smell.


Cuboidal cracking of timber or fibrous decay of timber


Weakened floorboards with a spongy feel


Fungal growth including web like - root like strands - mycelium


Bleaching of the wood

What is involved in Dry and Wet Rot diagnosis and treatment?

  • Identify source of moisture as a matter of urgency and eliminate the source to prevent the Dry Rot and Wet Rot from growing.
  • Once the source of the moisture has been eliminated, removal of plaster/affected timber.
  • Applying fungicide using a toxic box system of treatment. This is a process of drilling in a diamond pattern at staggered centres to enable the application of fungicide into the body of the wall, to separate masonry and fungal growth from replacement timbers.
  • A surface spray treatment to affected timbers and masonry.
  • Fixing any structural integrity issues caused by the outbreak affecting the timber. This final process may involve the removal and replacement of structural and decorative timbers.

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