Mold is a biological contaminant that can proliferate in the presence of moisture. Some types of mold can grow in very small quantities of moisture. The spores, bacteria and dust mites produced by mold may negatively affect a building's occupants, exacerbating allergies, and worsening or even causing respiratory problems, including asthma. Mold compromises a structure's integrity by eating away at the materials it grows on. Dampened materials may release potentially harmful gasses, as the moisture alters their chemical properties
Many building materials and practices that were thought to be efficient and economical when they were patented have turned out to be conducive to excessive, mold-causing moisture. Structures in warm, dry climates are sometimes built according to guidelines set out for cold, damp climates, resulting in unnecessary moisture and warmth becoming trapped inside walls. While advances in engineering and architectural research have provided new and innovative methods for building more moisture-resistant structures, mold and dampness problems in existing buildings pose major concerns that need to be addressed. Newer buildings with angular architectural flourishes and large windows may also be at an increased risk for leaks.