Properly insulating the attic, walls, floors and foundations of a home

Adequate insulation allows a home to resist cold or excessive heat while maintaining a comfortable indoor temperature for its occupants—without increasing the energy bill.

Here you will find advice on how to verify whether the insulation in your attic, foundations and exterior walls is sufficient.

Identify the areas that require insulation:

• Exterior walls;
• Roof and attic;
• Floors above unheated spaces (e.g. garage, crawl space);
• Basement and foundations.

Important points to keep in mind:

• Insulate your home from the basement to the attic to eliminate cold floors, condensation and mould, while helping reduce heating costs.
• Pay particular attention to framing elements during construction or renovation to ensure that they are fully covered by continuous insulating material.
• Make sure the insulation is installed continuously, covering all joints and junctions between components of the building envelope, such as transitions between walls, ceilings and floors in contact with outdoor air, the ground or adjacent unheated spaces.

If renovation projects planned, take the opportunity to improve the insulation of the room being renovated.

In all cases, good insulation must be paired with adequate ventilation to prevent condensation problems and ensure good indoor air quality.

Through the Rénoclimat government program, you may be eligible for financial assistance for insulation projects.

Under the Hydro-Québec LogisVert program, financial assistance may also be available for attic-insulation and caulking work.

Choose the program that best suits your needs and make sure you meet all eligibility requirements before applying.

There are several types of insulation: rigid boards, batts, loose-fill, injected or spray foam.

To be effective, insulation must:

• fill the cavity completely, leaving no voids;
• limit heat transfer;
• maintain performance over time;
• resist moisture (depending on the application).

Installation must always be done carefully. Even high-quality insulation loses efficiency if installed improperly.

Not all insulating materials are suitable for every area. For example, insulation that works well in an attic may not be appropriate for a basement wall, and vice versa.

R-value

Before choosing an insulating material, consider its R-value.

The R-value (or RSI value in the metric system) measures a material’s thermal resistance. The higher the value, the greater the material’s resistance to heat transfer—and therefore its insulating capacity.

The R-value is used to compare the efficiency of insulation products. For example, at equal thickness, an insulation material with an R-value of 5 is more efficient than one with an R-value of 2.

The R-value is also used to describe the level of insulation achieved after work is completed. In Québec, it is recommended that attic insulation reach an R-value of 50 or more.

Interior or exterior insulation

Although insulating a foundation wall from the inside improves a home’s energy efficiency, it does not allow you to benefit from the concrete’s thermal mass and it also reduces the interior living space (due to the insulation thickness).

In addition, insulating or adding insulation to a foundation wall from the inside increases the risk of freezing. If the soil is damp and the foundation is close to the frost line, it is better to leave an uninsulated strip at the base of the wall so that heat from the building can be transferred to the underlying ground.

Nevertheless, interior insulation is well suited for existing houses that do not require exterior excavation, as it is more accessible, less expensive and can be carried out in any season.

Only watertight and well-drained concrete foundations should be insulated from the inside. It is therefore important to check for cracks that could allow water infiltration from outside. Moisture caused by condensation during summer usually appears as a black deposit at the base of the wall, while infiltration from outside can be identified by whitish mineral deposits on the concrete surface.

If water infiltration or humidity problems cannot be resolved from the inside, corrective work must be performed from the outside. This may even be the ideal opportunity to add exterior insulation at the same time.

Interior insulation

For interior foundation-wall insulation, it is strongly recommended to use an insulation material resistant to moisture. Type 3 or 4 rigid polystyrene foam board is the material most commonly used for this purpose. However, since it is a combustible material, it must be covered with a fire-resistant coating to meet the fire-resistance level required by the current Construction Code. Mineral wool or fibreglass batts can also be effective if protected by a moisture-resistant membrane.

The total thermal resistance of a foundation-wall assembly should be about RSI 3.0 (R-17). Several techniques and combinations of materials can achieve this level of insulation. Two common methods are:

• Using extruded polystyrene rigid foam insulation with a minimum thickness of 76 mm (3 in.);
• Using Type 3 or 4 polystyrene foam at least 25 mm (1 in.) thick, combined with mineral-wool batts 89 mm (3 ½ in.) thick (R-12 batts), installed inside 2 × 4 stud framing (5 × 10 cm).

Exterior insulation

When foundation-drain repair is required, it can be advantageous to insulate the foundation from the outside. Remember that stone foundations and concrete-block foundations must always be insulated from the exterior. Exterior insulation also takes advantage of the concrete’s thermal mass, helping to maintain a more stable indoor temperature.

After excavating the foundation down to the footing, use Type 4 rigid polystyrene foam insulation with a minimum thickness of 76 mm (3 in.) over the full height of the wall. The insulation must be protected from sunlight. Use a waterproof membrane and high-quality granular backfill to keep the foundation dry.