What Causes Wood Rot?
The fungal spores that cause wood to rot are all around us. Fortunately, they are not always active, and rot damage does not occur overnight. Dry rot is a common type of wood rot in which wood is attacked by fungi. The fungi destroy the parts of the wood that make it strong and firm.
To grow, fungal spores need adequate amounts of water and high relative humidity. When the moisture content of the materials with which your home is built is coupled with high relative humidity, the stage is set for rot. For windows or siding, this often occurs when a small leak goes unnoticed and allows water to soak into the frame.