Insulating fibreboard tiles are occasionally used to finish ceilings in basements. Tiles vary in size from about 300 mm (12 in.) square to 400 × 800 mm (16 × 32 in.). The tiles are tongue and grooved and supported by concealed nails, clips or staples. They should be 12.7 mm (1⁄2 in.) thick when supported not more than 400 mm (16 in.) on centres. SUSTAINABLE HOUSING INSIGHT Healthy Indoor Environment Use low pollutant-emitting, water-based paint to finish gypsum board surfaces. Energy Efficiency Gypsum board is an effective air barrier when sealed to other components of the air barrier system, and can reduce heat lost through air leakage. Ensure that the various construction activities do not damage the air barrier system. Resource Efficiency Use local materials where possible and avoid those that must be transported long distances. Affordability Drywall is a durable and cost-effective finish for walls and ceilings. It is inexpensive to repair and maintain and is the preferred covering for most occupants. RELATED PUBLICATIONS About Your House: Accessible Housing by Design—Living Spaces, Canada Mortgage and Housing Corporation (product no. 66095) CAN/CGSB-19.22-M: Mildew-Resistant Sealing Compound for Tubs and Tiles, Canadian General Standard Board