Buildings are expected to have a useful life of three or four times the mortgage period. Moisture problems are considered the single largest factor in limiting that amount of time. With proper construction, the building envelope will help prevent problems like poor indoor air quality, water intrusion and mold. However, one small change can have can have dramatic effects on the entire structure and its occupants. It is common for homes and buildings that are constructed during rain or snow to have problems with mold during warmer temperatures and humidity. A material's reaction to moisture depends on a variety of factors including the ability to allow liquids or gases to pass through, absorption, evaporation, and susceptibility to damage and microbiological growth.