Dry Rot (Serpula lacrymans)

Dry-rot fungus is often thought of as a building cancer, rampaging through buildings and rapidly destroying any timber in its path

Dry Rot

The fungus, which thrives in moist un-ventilated conditions, will penetrate brickwork to get to more timber and can cause widespread destruction of structural timbers, skirting boards and door frames, and wood flooring.

In short, the fungus can be thought of as ‘living in masonry and eating wood’, and because the fungus thrives in damp, un-ventilated conditions, it can occur in the areas of a property that are not often seen, such as floor voids, or behind timber panelling, so damage may be extensive before the attack is discovered.

Identification of Dry Rot

It is important to identify whether timber decay has been caused by dry rot or another wood-destroying fungus such as one of the wet rots. This is because dry rot has the ability to travel through building materials other than timber, giving outbreaks the potential to spread quickly through a building. For this reason additional measures (e.g. masonry sterilisation) often have to be taken when treating dry rot outbreaks over and above those necessary when dealing with outbreaks of other wood-rotting fungi.

Typical indications of dry rot include:

  • Wood shrinks, darkens and cracks in a ‘cuboidal’ manner (see picture)
  • A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops under less humid conditions. This ‘skin’ can be peeled like a mushroom.
  • White, fluffy ‘cotton-wool’ mycelium develops under humid conditions. ‘Teardrops’ may develop on the growth.
  • Strands develop in the mycelium; these are brittle and when dry and crack when bent.
  • Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface has wide pores.
  • Rust red coloured spore dust frequently seen around fruiting bodies.
  • Active decay produces a musty, damp odour.

Important Note:

Dry rot can cause widespread structural damage. We recommend that you get professional advice and carry out a full survey if dry rot is suspected. If you suspect that you have Dry Rot then contact us. And we will arrange a survey.

Treatment:

The term dry-rot came from the belief that the fungus is able to transport moisture from a source many metres away, to attack dry wood. In fact, although the fungus can transport moisture over several metres, it cannot transport anywhere near enough moisture to attack wood that is otherwise dry.

Treating dry-rot can involve removal of the affected timber (including all timber for a metre beyond the visible signs of the fungus), and extensive chemical fungicide treatments for all adjacent timber and the brickwork of any contaminated walls and plaster.

Another approach is to use environmental controls, such as isolation and ventilation, which ensure that the damp, un-ventilated conditions required by dry-rot do not occur. The techniques are simple ways to ensure that the timber in a property does not become damp enough for dry-rot to attack, for instance replacing dry-rot decayed joists with new timber using joist hangers, instead of building them back into the brickwork, or by using ventilated skirting board details to encourage ventilation of a floor void.

Replacement door frames and joists should have a strip of damp-proof membrane around the outside, to fully isolate them from damp or potentially damp brickwork, so the timber would never become damp enough for dry-rot to ‘eat’.

If you have dry rot, it is probably best to have the problem looked at, and corrective action taken. Ignoring this problem can become a very costly affair!

See some of our successful projects below

Damp

Wet Rot

Condensation

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