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Building Science by Norman Aceron Garcia

Foundation insulation

by Norman Aceron Garcia


Heat lost from a conditioned and un-insulated basement can be as high as 50 per cent of a home’s total heat loss in a well-insulated and tightly sealed home. Foundation insulation is designed mainly to lessen heating costs and has very little effect in reducing cooling costs. More so, foundation insulation improves the liveability of basement rooms, increases inhabitants’ comfort, and lowers the risk for mould growth resulting from condensation build-up.

There most common residential foundations types are full basement, slab-on-grade, and crawlspace. A full basement is recommended on locations that have low water tables and deep frost lines. Most old homes normally have crawlspaces. In some parts of Canada, it is common to see slab-on-grade foundations in homes with a walk-out basement.

Full basements can be insulated either on the exterior or interior. Usually, 2x4 lumber framing with wet-spray or batt insulation covered with drywall are used in interior insulation. Rigid foam insulation secured with furring strips are also installed on basement interiors. Extruded or expanded polystyrene can be used for both exterior or interior, but any above-grade insulation that is exposed should be sheltered to guard it from ultraviolet rays and physical damage. Common protective materials include the application of a stucco-like finish, cement board attached to the sill plate, and roll-metal stock to match the siding.

Crawlspaces are just short basements meant as access to plumbing lines, electrical conduits, and HVAC ducts in older homes. Common insulation systems installed in crawlspaces are exterior foam and foam-form insulation systems. However, interior crawlspace wall insulation is typically either foam board or draped insulation. If foam insulation is installed, it must extend from the top of the footing to the top of the foundation. The void spaces between the rim joists must be packed with fiberglass batts or a foam-in-place product. Most fire codes permit up to 50 millimeters of polystyrene exposed on the interior of a crawlspace before covering is installed.

Several jurisdictions call for a ventilated crawlspace to manage moisture. Vent provisions are considerably lessened if the crawlspace floor is covered with plastic sheeting with overlapped sides and taped to reduce moisture. The floor above the crawlspace can also be insulated to raise the thermal envelope between the floor and crawlspace walls. Also, plumbing piping and heating and cooling ducts within the crawlspace must be insulated accordingly.

The heat loss on slab-on-grade foundations is maximum at or adjacent the exterior grade. Proper insulation is critical in slab-on-grade foundations in order to reduce the cold-floor syndrome and lower the heating costs. Exterior foam insulation that is also used in exterior basements can be installed. The insulation must extend from the top of the footing to the top of the slab. It is required to allow for a thermal break to avoid thermal wicking from the slab to the outside. Use of a bevelled slab edge or a pressure-treated nailer can provide the necessary thermal break and attachment substrate to finish floor covering.

In summary, energy savings can be achieved by considering the best insulation system appropriate for the type of foundation. The determination of the most cost-effective insulation solution to foundations depends on several factors such as the type of foundation, efficiency of heating equipment, cost of natural gas, and climate.

Norman Aceron Garcia is a Professional Engineer of Mr. Peg Property Inspections Inc. Please email for free technical consultation.

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