Why does mould grow in homes or buildings?

Moulds and fungi are found in nature and are necessary for the breakdown of leaves, wood and other plant debris. These micro-organisms can enter a building directly or by their spores being carried in by the air. In a home or building, moulds and fungi are usually found growing on wood, drywall (plaster/gypsum/Sheetrock(R)), upholstery, fabric, wallpaper, drapery, ceiling tiles, and carpeting.