Ceilings

In a home with a vented attic, the ceiling provides the air barrier. The ceiling air barrier, which usually consists of taped, mudded drywall, should be continuous and all holes through it for wiring, electrical boxes, light fixtures, flue and chimney pipes, duct chases, heating registers, soffits, etc., should be thoroughly air sealed before insulation is installed. To help maintain consistent insulation over this ceiling air barrier, wind dams and baffles should be installed in the attic in every rafter bay that has a soffit vent. A wind dam consists of a piece of rigid material (rigid foam, OSB, plywood, etc., that is installed vertically just outside of the top plate and extending up to the baffle to direct ventilation air up from the soffit vent to the underside of the roof. It prevents wind that enters the soffit vent from pushing insulation away from the eaves and it also provides a "backstop" when insulation is installed to keep it from falling through the soffit vent. It is important to maintain a minimum amount of insulation, preferably equivalent to the insulation depth of the rest of the attic, over the top plates of the exterior walls. This will prevent cold spots along the exterior walls and ensure a consistent R-value across the ceiling. Building the roof with raised heel “energy” trusses will allow the full height of insulation to be installed over the top plates.