Dry rot is a weakening of wood caused by one of several species of Fungus.
The fungus digests the parts of the wood that give the wood strength and stiffness.
Weakened wood is typically somewhat dry, hence the name dry rot, and brittle
The Dry Rot Fungus has the unusual ability to transport water from wet areas to dry areas allowing the fungus to grow even in relatively dry wood.
Dry rot usually results from too much moisture in contact with wood. If not stopped the dry rot fungus will so weaken wood that it may eventually disintegrate.