dry rot

what is the issue?

Do I have a Dry Rot Problem?

Dry rot or Serpula Lacrymans is the term given to a fungus that destroys unprotected timbers. It is a very serious timber condition that often does damage to timbers that are hidden from view, behind wall finishes under floors. All wood-decaying fungi need moisture before decay begins so to be called ‘dry rot’ is not entirely true. Damp problems and damp patches can be the cause of dry rot. Making sure damp and mould is avoided through extractor fans and opening windows, will allow air to circulate. Identifying the cause and type of dampness or mould is a crucial part of tackling these issues.

let’s find the cause

main causes

Dry rot can occur in a property where unprotected or untreated timber has become damp. Timber is at risk of a fungal attack when the moisture content of the timber is over 20%. Dry rot is unique to wood rotting fungi in that it does not need sunlight to grow. There are many reasons that can cause timber to become damp. Leaks from showers, washing machines and external issues such as rising and penetrating damp are a few of the reasons it can occur.

Dry Rot Identification is very important, as there are other wood funguses such as wet rot which can destroy timbers. Dry rot can travel up brickwork/masonry beneath the plaster finishes. It will try to locate the next source of timber to attack and has the potential to spread quickly. This means masonry sterilization is required when dealing with dry rot, but not when dealing with other wood rotting fungi. Signs to look out for when identifying dry rot are


Spores can exist everywhere. Individually they cannot be detected by the human eye, however when in large numbers they appear as orange and brown dust. This is one of the simplest ways of identifying a dry rot issue. The life-cycle of dry rot begins when spores come in contact with timber in a favourable environment.

sporophore (fruiting body)

Like any life form, dry rot can be stopped by a lack of air, food or water. These are identified by their pizza like appearance, round in shape and rusty red in colour. Dry rot has a unique way of restoring vital elements imperative to its continuation. The dry rot will produce a self-reproduction organ known as a sporophore. This allows the spore-bearing surface to shed orange/red coloured spores. This unleashes into the atmosphere in the hope that the spores can land once again in the right environment. They will then carry on germinating; this extends the growth period of the dry rot. Once on the timber, the spore will germinate and produce Hyphae growth.


Hyphae act as the root of the rot, sending out fine strands to grow through the timber. The hyphae will then feed on the sugars within the timber. The dry rot fungi/fungus produces enzymes to split the sugars, reversing the formation of the wood. The removal of these sugars results in cross grain cuboidal cracking, reducing the timber to an unsound structural state. Hyphae then multiply generating mycelium growth, a fluffy cotton-wool like substance.


Mycelium growth will develop under humid conditions and appear as white or grey cotton wool-like substance. Mycelium can spread across many building materials in search of a new source of food. This will lead to the progressive damage of timbers throughout the whole property.  It also can lay dormant if the structure of the property dries out. This can continue for up to ten years and if conditions become favourable will spring back to life! Strands will develop in the mycelium these become brittle when dry and will crack if bent. 



Firstly, we will need to identify and eradicate the source of moisture sustaining the attack. This is important to prevent further outbreaks occurring. By controlling moisture, it will ensure the structure dries out and stops any dry rot spores form germinating. We will then be able to find the full extent of the dry rot damage.

The now identified timbers will now have to be filed down to a suitable point. We cut back at least 500mm beyond the last signs of hyphae strands. Cleaning the walls of any remaining growth will prepare them for treatment. We can replace the rot with pre-treated timber and use treatment fluid on any undamaged parts. This will kill dry rot and stop re-infestation. We will also sterilise the masonry to prevent any further outbreaks in future.

Some areas of an outbreak will also need to be treated with a masonry biocide and fungicide pastes. This will prevent a further attack by wood-rotting fungi or wood boring insects. The biocide is designed to penetrate the substrate. This will stop the spreading and will control and stop the growth of dry rot and fungi.

If you’re not sure what treatment is right for you, please contact us!

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