What is the difference between Dry and Wet Rot?

Rot is one of the major causes of timber decay in old and even modern buildings. The two most common types of wood rot include wet rot and dry rot, which are caused by fungal decay in building timbers.


Dry Rot

Is only caused by serpula lacrymans (see page two for more details) and is the most serious form of fungal decay in a building. It can spread onto and destroy much of the timber. Signs for dry rot:

  • Distinct mushroom smell
  • White fungal growth with yellow and lilac tinges
  • Deep cracks appear within the wood
  • Both soft and hardwoods can be damaged

Wet Rot

Occurs more frequently, but is less serious; decay is typically confined to the area where timber has become and remains wet. Signs of wet rot :

  • Distortion, discolouration, softness and cracking
  • Loss of strength to the timber
  • Visible fungal growth – this may sometimes occur
  • Smell – there may be a damp musty smell

Outbreaks of dry and wet rot start in similar ways. The mature fruiting bodies of wood-destroying fungi that develop during an attack produce millions of microscopic spores and these are widely dispersed by air currents. If they fall on untreated damp wood they will germinate by pushing out a hollow tube called a hypha which grows and branches to form a mass of hyphal threads called mycelium.

This develops inside the timber and breaks down the wood for food. The timber may darken in colour and develop a characteristic cracked appearance. Some wet rots may result in bleaching of the wood; these are more common in doors and window frames. Eventually, the wood loses its strength and in some situations may become dangerously unsafe.

What Is The Difference?

The main differences between dry rot and wet rot are 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 two types of decay be distinguished since they require different treatment.

How To Treat Dry & Wet Rot?

Both need professional diagnosis and treatment.

Dry Rot Treatment Plan

  1. Locate and eliminate the source of moisture which is maintaining the rot. This will require repairing defects such as overflowing or damaged gutters, missing slates, blocked air bricks etc.
  2. Remove all decayed wood and damaged linings, panelling, skirting’s, ceilings and plaster to prevent any further spread of the fungus.
  3. Eliminate the visible and accessible fungal growth.
  4. Apply fungicidal treatment to the remaining timber and brickwork to form protective chemical barriers.
  5. Replace all removed timber with preservative-treated timbers.

Wet Rot Treatment Plan

  1. Ensure the source of damp or water ingress is cured, so that timber moisture content can fall to a safe level (below 20%).
  2. Remove weakened wood.
  3. Apply fungicidal treatment to the remaining timber at risk.
  4. Replace all removed timber with preservative- treated wood.

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