Air barriers are added to the outside of the sheathing and prevent wind and air infiltration. It was discovered about forty years ago that adding an air barrier increased the buildings energy efficiency.  New barriers have been developed that hold back rain water and also allow moisture vapour from the building cavity to escape.

A vapour barrier is used on the warm side or interior face of the insulated stud wall. The vapour barrier prevents moisture in the air entering the home. During the winter especially, when cold air meets warm air from inside, condensation would occur if the vapour barrier were not in place.  Condensation left alone will create mildew and rot, so from a health and structural point of view the vapour barrier is essential.  Typically vapour barriers are made of polyethylene sheets and are stapled to the inside stud face and sealed with mastic at the seams.

Insulation is used in wood frame construction and is placed between timber members. As wood is a natural insulator, the combination of wood and insulation creates an envelope around the entire living space. Insulation in the ceiling is thicker to prevent rising heat escaping. There are different types of insulation used in a house; the most common is fiberglass batt insulation. Rigid insulation is generally used on the exterior of foundation walls and applied over the entire wall structure to increase the insulation rating or R value as it is known. Sprayed insulation has recently been introduced into the residential industry and combines a tighter seal between the studs reducing air leakage.