While previous generations adapted themselves to homes with little insulation, most people today want to live in warm, comfortable houses. Today, a healthy home must be airtight, well-insulated and well ventilated.
Properly insulating a home is like putting on the right clothing for the weather. A wool sweater will keep you warm if there is no wind or rain. On windy or rainy days, you need to cover the wool with a nylon jacket to stay warm and dry. The same is true for a house. On the outside, just under the brick or siding, there is an air barrier that plays the same role as nylon: it prevents wind from blowing through.
Then comes the insulation (like your sweater), and the vapor barrier. This prevents moisture from reaching the structure where it could cause damage.
The attic is often the most effective place to add insulation. Usually a contractor sprays loose-fill insulation between and above ceiling joists.
The ceiling air barrier must be airtight enough to ensure that hot and humid air from the house does not reach the attic, where it is colder, as this can cause condensation in winter. Check air leakage through the ceiling, at the top of the interior walls and near penetrations such as plumbing stacks.
Soffits must not be blocked by insulation; it may be necessary to install deflectors.
The walls of the basement are unique because they need to prevent substantial moisture movements from both inside and outside the home.
Sprayed polyurethane insulation is rigid and rot-proof, and it retains its insulating properties for life. Since it adheres to the wall, it does not settle and does not degrade over time, unlike mineral insulation. A polyurethane spray application provides the perfect air and moisture barrier. Its continuous line also eliminates thermal bridges, contributing to significant energy and cost savings.
Never install insulation in a basement with moisture problems. Solve the moisture infiltration problems before installing insulation (see the Guide to Fixing your Damp Basement published by the CMHC).