Energy Efficiency E-Library > Structural Info > Basement Insulation

Basement Insulation

Crawlspaces

In the past, insulation of basements and crawlspaces was often overlooked as a means of energy efficiency. Today, more basements are insulated and in B.C. it is a Building Code requirement for new homes.

In an unheated or vented crawlspace, insulation can be installed on the underside of the floor over the crawlspace. Fiberglass batts or blankets are the easiest material to use in this type of application. This insulation can be held in place with wire mesh, spring metal supports called "tiger claws," or wire or fishing line criss-crossed between floor joists.

Crawlspaces with dirt or gravel floors should have a 6 -10 mil plastic ground cover to prevent moisture from evaporating into the air in the crawlspace. Ten mil is recommended, as it is less likely to be damaged by walking on it. The ground cover should be overlapped 10 to 15 cm (4" to 6") at seams and at the bottom of the foundation wall. The material can be held in place with bricks, small sections of framing lumber, or other objects heavy enough to prevent it from being disturbed if someone walks on it.

Any ducts that pass through an unheated crawlspace should be sealed and insulated, to prevent air and heat loss. Water pipes should be insulated to prevent freezing. In colder parts of the province, unheated crawlspaces are not advisable. They should be insulated and at least partially heated.

If the crawlspace is unvented and contains a heating system, water heater or significant heat source, you should insulate the crawlspace walls instead to contain the heat and warm the floor above. You can use fiberglass batts or blankets or one of the various foam board insulation materials. If using the foam boards, check with your building inspector, as under some circumstances it is advisable to cover the insulation with a fire retardant material.

Basements

Insulate basement walls to improve both energy efficiency and comfort.

With new construction you can insulate the interior or exterior of the foundation wall. If insulating the exterior, use several inches of foam board insulation (enough to achieve R-12) down to the footing. If insulating on the inside, use fiberglass batts or foam board on the full height of the wall (R-12 or greater is recommended). Foam board used in a basement must be protected with drywall, plywood or some other types of wood-based materials. Check with your local building inspection department for a list of approved materials. There are also some new methods in which the insulation is incorporated into the foundation wall itself.

When insulating a basement wall in an existing home, insulation is mostly limited to the interior of the wall. Depending on the use of the basement you may choose to either finish the walls or use techniques that do not require creating a finished basement.

Slab on Grade Foundations

The majority of the heat loss from a slab on grade foundation occurs at the edges where the slab is exposed to the outside air. Insulating around the exposed perimeter of the slab will help reduce this loss. Use rigid foam board insulation and extend it down below the frost line, or 0.6 metres (2 feet), whichever is greater.

In new construction or cases where a sub-floor can be installed, 5 cm (2 inches) of foam insulation can be used either under the slab or as part of the sub-floor. This is generally considered cost-effective only in very cold climates.

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