Insulating Your House from CMHC Series 6-10

Wall Insulation for Existing Construction

The two most common wall types are wood-frame and solid brick. In a wood-frame wall, insulation (loose fill and some foams) is typically blown into the cavities through holes that have been drilled through the drywall or siding. In solid brick, the largest cavity is usually 25 mm (1 in.) wide, which is not enough for any significant increase in R value. The builder must create a cavity. Usually, a new cavity wall is built inside and insulated as a new wall, or board stock and new siding are applied to the exterior. When planning a cavity wall retrofit, remember the following:

• The cost of getting at and repairing the walls is a significant part of the work and cost of the project.
• Both air and vapour barriers are required. The interior painted drywall can be both an air and vapour barrier, but details at windows, electrical outlets, floors and other penetrations must be done carefully to reduce air movement through the wall as much as possible. Air movement can lead to mold growth and decay of the walls, as well as loss of insulation efficiency.
• An insulation must be selected that will completely fill the cavity and not settle. Some insulations, such as foams, can provide reasonable air barriers themselves.