Insulating Your Walls

Walls can account for 10 to 30 per cent of heat loss in houses. In addition to heat loss through the walls, there are many cracks and penetrations that allow uncontrolled air leakage into and out of the house. Upgrading wall insulation and controlling air leakage are the two main components to making your home more comfortable and energy efficient.
 

New home construction provides an opportunity to install a continuous vapour barrier and high levels of insulation in an efficient and cost-effective way. Walls in most homes built today are framed with 2 x 6 construction and insulated with 6 inches of fiberglass batt insulation. The insulation rating on these walls is R-19. However, homes built with 2 x 4 exterior walls are insulated with 4 inches of fiberglass batt insulation which is equivalent to R-12.

Building a new home gives you an opportunity to take measures to control air leakage by installing the appropriate moisture and vapour barriers and sealing them properly. A continuous vapour barrier should be located on the warm side of the insulation.
 

Many older houses are improperly insulated, if there is any insulation at all. This can have a large impact on your heating and cooling costs. Loose-fill insulation can be blown into your walls and attic to help increase the efficiency of your house, significantly decreasing your heating and cooling expenses and increasing the comfort of your home.

Insulating the walls of an existing home takes a little more consideration than a basement or attic. There are three ways you can upgrade the wall insulation in your home. You can insulate from the inside, insulate from the outside or insulate the wall cavity.

Insulating from the inside may be an option if you are doing an extensive renovation inside. To insulate the inside wall you can either rebuild the existing wall or build a new wall over the existing one.

Insulating from the outside can be easily done and is more viable if you plan to replace siding, windows or doors. It is also an option for walls that cannot be treated with blow-in insulation.
 

The most common method and least expensive, is to insulate the wall cavity with blown-in insulation. However, it works best for walls that contain no insulation, and where there is no evidence of moisture. It is extremely important that walls and ceilings be covered with some type of vapour barrier. Using a vapour barrier paint and sealing leakage points on the inside wall, is usually sufficient. However, two coats of oil-base paint is not an adequate vapour barrier.

Blown-in insulation should be done by an experienced contractor. The insulation should be blown-in using special pressurized equipment, which significantly reduces the amount of settling of loose-fill insulation after installation. The contractor must be thorough to ensure each cavity is filled with insulation. This includes:

1. Identifying cross blocking (fire-stops) in the walls, and ensuring that holes are drilled to give access to all spaces in the walls.

2. Filling hollow corner posts, the area under bay windows, overhangs and other odd spots in older, more ornate homes.

3. After the final inspection, making sure the drill holes are filled with a cork and a high-quality exterior caulking.
 

Insulating the exterior walls can be done by installing a rigid board insulation or a batt insulation between the existing siding and the new siding. Consider the following if you plan to insulate the outside wall.

1. Remove portions of the exterior wall from different areas of the house, including corner and base boards, to see if the wall construction has been damaged by moisture. If it has been, repair it before you continue.

2. Apply a 6-mil polyethylene vapour barrier over the entire outside wall area, caulking it at the top, bottom and sides. Overlap about two feet of the barrier at the corners.

3. If you use fibreglass batts, you must construct a frame to support the insulation. If you use a rigid insulation such as extruded polystyrene, it may be acceptable to use no framing or a very light strapping. Fasten the insulation directly to the old surface.

4. Install the insulation according to the manufacturer’s instructions. Ensure that the R-value of the new insulation is at least twice that of the existing insulation; this ensures there will be no condensation on the warm (inner) side of the new vapour barrier.

5. Sheath with a permeable, light board (not a composition or ply-board) and finish with siding or clapboard.
 

Getting air leakage under control involves a combination of a wind barrier, vapour barrier and air sealing. Wind barriers are installed on the cold side of the insulation and serves to keep moisture out. However, it also has a unique property that allows moisture inside the wall to escape to the outside. Continuously sealed vapour barriers are installed on the warm side of the insulation and serve to prevent moisture inside the house from getting into the wall cavity.

Air sealing involves minimizing the amount of air moving in and out of your home. However, any hole in the building envelope has potential for uncontrolled air flows. Ensure the following areas are sealed well.

• Around windows and doors
• Electrical outlets
• Exhaust fans and dryer vents
• Baseboards
• Fireplace dampers
• Sliding doors
• Plumbing pipes
• Ductwork

To obtain more information on insulating your walls, click here to view Natural Resource Canada's publication “Keeping The Heat In” online or to order a printed copy.