Dry rot is a wood condition that is caused by fungus. According to LivingWithBugs.com, dry rot occurs from too much moisture. Typically, wood that has dry rot is brittle and weak.
The best way to prevent dry rot is by getting rid of excess moisture. Wood does not have to be completely wet for dry rot to occur. Dry rot fungus damages wood by taking moisture from wet areas of wood and transporting it to dry areas of the wood, which eventually causes the wood to rot. Wood that already has dry rot can be treated with fungicides such as boric acid or borate.