Moulds and fungi occur naturally in the environment and can enter a building, either directly or as spores carried in the air. Mould needs moisture to grow and can be found growing on drywall, carpeting, ceiling tile and wood in wet or damp areas of a building. Areas most susceptible to mould growth include basements, washrooms and cooking areas. Tightly sealed buildings may also be more susceptible to mould growth because of high humidity.

The presence of mould in a building represents a potential health concern. Not all people will experience health related problems on exposure to mould. Those that do may will experience a number of symptoms such as runny nose, cough or congestion, headache, fatigue or eye irritation. Other symptoms may be present. Exposure to mould may result in more serious problems for anyone who has asthma, allergies or a suppressed immune system.