Keeping Wood Dry Isn’t Always Enough: Beware of Dry Rot

Build Green: Wood Can Last for Centuries by Carol Clausen and Samuel Glass tells us that most wood-decay problems only occur when decay fungi grow in wet wood. But one kind of fungus is uniquely capable of transporting its own water from a source of moisture (usually soil) into wood that is typically too dry to decay. While decay by such water-conducting fungi is uncommon, when it occurs, it is devastating.


Dry rot starts when an infected piece of wood forms a bridge between soil and other wood in a house (Photo by Carol Clausen, FPL).

Large areas of flooring and walls can be destroyed each year unless the fungus is stopped. Ironically, it may be the easiest fungus to prevent or control. Unlike typical decay fungi that start growing from airborne spores, water-conducting fungi usually start growing from previously infected lumber that forms a bridge between the soil and other wood in the house. This can happen if old, discarded beams that have been lying on the ground are used in home repairs or additions; new wood has been improperly stored in contact with soil; or infected wood waste is used as fill under a porch or addition. This type of decay can be stopped by simply breaking the contact between susceptible wood and the source of moisture. Once the water supply is broken and the infected wood dries, the fungus will die.

Good news for the homeowner: a potentially destructive source of rot is easy to control with attention and care.