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Wood Decay Fungi

  • Wood Decay Fungi ( wood rot), are filamentous organisms which begin as microscopic spores that land on the surface of the wood and germinate to produce thin strand-like cells called hyphae. Hyphae grow through the wood and secrete enzymes which degrade and weaken the wood.

Decay requires: 

  1. adequate moisture
  2. ambient temperature (32º to 110º)
  3. oxygen
  4. a food source.

Wood moisture levels above 20-30% are considered conducive to wood fungal rot. Damaged wood typically will need to be replaced. Ultimately the source of moisture must be eliminated even if all of the fungal organism cannot be eliminated.

Common types of wood decay in buildings:

  • Brown rot: This type of decay causes the wood to break down into brown cubes that split against the grain. Advanced stages of brown decay result in dry, powdery wood that is unable to support much weight and crumbles easily.
  • White rot: This type of decay appears whitish, stringy and mushy, and tends to be more common in hardwoods.
  • Dry rot: A misnomer, this term has been used to describe decayed wood that has since dried and ceased decaying. Some people may erroneously assume that the wood is still in the process of decay. Moisture is required for wood decay to occur, so no literal “dry rot” exists.
  • Wet Rot: The two types of wet rot, brown and white can both be destructive to timber, they have a different effect upon the wood depending upon type. Generally, brown rots cause cuboidal cracking & shrinkage of the timber whilst white rots tend to reduce the timber to a stringy, fibrous texture. 

There are other things associated with wood decay such as mold. Although mold doesn't require moisture levels to be at the levels of decay it still can cause serious repair expenses and health issues. 

This is a concern for Attic moisture. Common issues with roof sheathing are wood rot due to poor building air sealing which contributes to condensation in colder months allowing the roof sheathing to reach dew point and cause mold.