Insulation

Insulating the foundations and insulating the roof of your home will help it withstand extremes of cold or heat while maintaining a comfortable indoor temperature, thereby avoiding exorbitant energy bills.

Without adequate insulation, your house risks losing substantial amounts of heat. Depending on the configuration of your house, heat loss may be broken down as follows:

  • 17% through above-ground walls;
  • 15% through basement walls and the foundation footings;
  • 11% through the roof.

Poor insulation may also be responsible for a host of other problems such as cold floors and walls, condensation at the wall base and even traces of mold. Insulating your house therefore can make all the difference.

Insulation procedures and materials

There are various types of insulating materials: rigid foam panels, fibreglass batts, loose cellulose fibre, injected and foam insulation. To be effective, the insulating material should:

  • uniformly fill the space to be insulated;
  • be resistant to heat transfer;
  • be long-lasting;
  • resist humidity (in certain cases).

Its thermal resistance or R factor (RSI in the metric system) indicates an insulating material’s performance. The higher the R or RSI value, the more resistant it is to heat transfer and the better it works as insulation. However, regardless of the insulation material used, its installation must be flawless because its thermal resistance depends on how well it is installed. In addition to its thermal resistance (R) and the associated cost, the first and foremost consideration when selecting insulating material should be its destined use. For example, certain materials are not suitable for insulating a basement but are perfect for insulating an attic.

Is your house well insulated?

Do you have any construction or renovation plans? Here are a few important things to consider when you start:

  • Insulating your house from the basement to the attic will not only eliminate the problems of cold floors, condensation and mold, but will also reduce your heating costs.
  • Pay special attention to structural components during any construction or renovation to make sure that these are coated with an insulating material that is laid down in a continuous fashion over the entire surface.
  • Make sure that the insulation is installed in a continuous fashion so that it covers all the joints and seams such as the transitions between walls, ceilings and floors in contact with the outside air, the ground or an adjacent unheated space.

Insulation that has been well planned and installed during your construction or renovation project will make your house more comfortable and reduce your energy bill.

How should I insulate a concrete foundation wall?

The following text provides guidelines on insulating foundation walls , whether from both the inside or and the outside. 

  • Should I insulate from the inside or from the outside?

Although it helps to improve the energy efficiency of the homehouse, insulating foundation walls from the inside does not benefit the thermal mass of concrete and also reduces the inside space (thickness of the insulation).

In addition, insulating or increasing insulation of a foundation wall from the inside increases the risk of freezing. If the ground is damp and the foundations are close to the frost line, it is best to leave a non-insulated space at the base of the wall so that the heat from the building can be transmitted to the underlying soil.

Nevertheless insulating from inside is well suited to existing homehouses that do not require any outdoor excavation work since this is a more accessible method, it is cheaper and feasible in any season.

It should be noted that only sealed and well-drained concrete foundations should be insulated from the inside. For this, it is important to check for any cracks that might be the source of water infiltration from the outside. Humidity caused by condensation during summer usually causes black stains at the base of the wall, while infiltration from the outside can be detected by the appearance of a white deposit (mineral salts) on the concrete surface.

If water infiltration is detected or if humidity problems cannot be resolved from inside, adjustments will need to be made from the outside. Where necessary, this may even be the perfect opportunity to work on the insulation from the outside.

  • Insulation from the inside

For insulation of a foundation wall from the inside, the use of moisture-resistant insulation is strongly recommended. Type 3 or 4 rigid polystyrene insulation is the most commonly used material for this purpose. Since it is a combustible material, it is important to cover it with a firewall to meet the fire resistance level required by the current building code. Mineral wool or glass wool also works well if protected by a waterproof membrane.

The total thermal resistance of a foundation wall should be around RSI 3.0 (R-17) for the complete assembly. Several techniques and combinations of materials can achieve this level of insulation. Use of 76 mm (3 in.) thick extruded polystyrene rigid insulation or use of type 3 or 4 polystyrene at least 25 mm (1 in.) thick combined with 89 mm (3½ in.) thick mineral wool mat (R-12 wool), installed inside a two-by-four (5 by 10 cm) stud, are two of the most commonly used techniques to achieve this goal.

  • Insulation from the outside

Where perimeter drainage rehabilitation is required, it may be advantageous to isolate the foundation externally. Stone foundations and concrete block foundations must be insulated from the outside. In addition, exterior insulation provides the benefit of the thermal mass effect of concrete, which should ensure a better balance of interior temperature. After the foundation has been excavated to the wheelbase, it is suggested to use rigid polystyrene insulation type 4, with a minimum thickness of 76 mm (3 in.) throughout the height of the wall. It is necessary to protect the insulation from sunlight. Using a waterproof membrane and high-quality granular fill will ensure a dry foundation.

Share this page

 

Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs

© Gouvernement du Québec, 2008-2022