Some frequently asked questions about residential foundation insulation

If a basement is unfinished does it still need foundation insulation ?    Yes, unless the floor above is insulated. Even if used only for storage and heating and cooling equipment the basement is thermally connected to the rest of the house.

Is floor insulation above a basement or a crawl space an alternative to foundation insulation ?  Yes, but keep in mind that pipes, ducts and HVAC equipment located in the basement would then need to be insulated to meet the MEC and to protect pipes from freezing. Sometimes these can be grouped in a small area with insulated walls while the floor above the rest of the basement is insulated.

Doesn't placing insulation on the exerior improve energy performance ?  If the basement incorporates passive solar design with a significant amount of south facing windows, exterior insulation will be beneficial, provided the walls are exposed to solar gain. In a typical basement the energy savings are negligible.

Should the interior of foundation walls have vapor barriers ?  Yes, if interior insulation is used. The concrete must be allowed to dry, but moist basement air typical of the Midwest summers should not be allowed to reach the cool wall where it can condense. Batt insulation specifically designed for the interior of foundation walls has a perforated poly facing that prevents air from circulating through the batt, but allows water vapor from the wall to escape.

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