Dry Rot Damage & Treatment

What is dry rot?

Dry rot (right) is a weakening of wood caused by one of several species of fungus. The fungus digests the parts of the wood that give it strength and stiffness. Weakened wood is typically somewhat dry, hence the name "dry rot", and brittle and may have a "blocky" appearance.

Ironically, dry rot usually results from too much moisture in contact with wood. The fungus has the unusual ability to transport water from wet areas to dry areas allowing the fungus to grow in, and infect, dry wood. If not stopped the dry rot fungus will so weaken wood that it may eventually disintegrate.

Can dry rot be confused with other damage?

Yes. Dry rot is often confused with carpenter ant or termite damage. Carpenter ant damage is marked by the removal of wood and formation of clean cavities where ants live. Subterranean termite damage is similar to dry rot in overall appearance but the presence of live termites, termite galleries and generally wetter wood can usually distinguish the two conditions.

How do I prevent dry rot damage?

The most important way to prevent dry rot damage is to reduce or eliminate excess moisture. This may be as simple as repairing a leaky pipe or as complicated as stopping water infiltration through a basement foundation. A common cause of dry rot and termite damage is wood in contact with soil as occurs with a failed foundation.

If moisture cannot be controlled then wood should be treated to inhibit fungal growth. Boric acid, or borate, is an excellent fungicide against the dry rot fungus. Borate also prevents insect damage. However, most forms of borate should not be used if liquid water is present because borates are water soluble and will wash away. In these situations use fused borate that is made for exterior use.