There are three main types of wall construction used in Canadian houses.

i) Solid walls

Solid walls - built of brick, stone, concrete block, log or wood plank - do not have a cavity that can be insulated. The only option is to add insulation to the exterior or to the interior. Many solid walls, including double brick walls (see Figure 7-1), have a small cavity, generally less than 25 mm (1 in.), which is a drainage plane that collects and drains water out of the wall. Never insulate these cavities or plug their drain holes.

ii) Concrete block

Concrete-block walls usually have hollow cores that allow air circulation within, increasing convective heat losses. Insulating the cores offers minimal thermal resistance since the block's internal webs and mortar will continue to act as thermal bridges. Instead, seal all possible air leakage routes into the block wall and ensure that the top course of blocks is capped. Where block walls form the party walls between housing units, air leakage often occurs in the space between the block wall and the interior finish. Make sure the space is fully air sealed.

iii) Frame walls

Frame walls have a cavity that may be insulated. Different construction techniques determine the size of the cavity and ease of access from either the interior or exterior. The wall construction also affects details that can interfere with the insulation, including top and bottom plates, fire stops, blocking, plumbing, wiring and heating ducts. A frame house with a brick veneer usually has a 25 to 50 mm (1 to 2 in.) air space between the bricks and the frame wall as part of the drainage plane. Do not insulate this space. Furthermore, insulating over the surface of an exterior wall that includes a drainage plane air space will simply not be very effective. It is better to add the insulation directly to the exterior of the frame wall and then incorporate the appropriate air barrier, drainage plane and siding, unless the specific product and its installation directions account for these requirements. The larger cavity in the frame wall can be insulated.

Opportunities for upgrading

Using dense-pack insulation techniques, empty cavity and some partially insulated cavity frame walls can be insulated from the top and bottom or from the interior or exterior. Insulating should include air sealing as described in Chapter 4, "Comprehensive air leakage control."

Walls can be insulated as part of a major repair job or renovation. Interior work includes wall repairs, electrical wiring upgrades, insulation and vapour barrier installation, drywall and finishing. On the exterior, insulating can be combined with re-siding.

Address any moisture or structural problems before insulating. Indications of problems include staining, mould growth, rot, cracks on the inside and exterior wall finishes, and windows and doors that do not operate properly because they are out of square.

It is important to consider both vapour barriers and air barriers, especially when adding insulation to the interior or exterior of an existing wall. The vapour barrier must be on the warm third of the finished wall (see Figure 2-12 for more details). Also consider the location and condition of old vapour barriers, which could be as simple as plaster walls with several coats of paint.