foam board thickness - 1' or 2' ?

phoenix2000February 14, 2008

Aside from the extra benefit of greater insulation from 2" vs. 1" foam board being applied to basement walls before framing, are there significantly greater moisture control benefits between the 2" thickness vs. 1" thickness?

Code is requiring we use kraft insulation in the framing,so insulation level is not an issue. Does the 1" foam board adequately control potential moisture issues or should I spend a little extra money and get the 2" thickness to maximize moisture control? Is 2" thickness harder to install?

Does this answer change if we use metal framing?



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Assuming you're in a Cold Zone, not a Very Cold Zone, one inch XPS is sufficient. (For EPS, I'd put in two inches.) It just means you'll need a little more of whatever other insulation you are putting in between the studs. Same for metal framing. Just be sure the base is on 1" XPS; metal framing doesn't take kindly to water.

    Bookmark   February 15, 2008 at 2:01PM
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Worthy, if I install 2" board or 1.5", and then frame a 2x4 wall, do I need to install insulation (regular stuff) in the 2x4 cavity? Or does it get empty?

    Bookmark   February 16, 2008 at 10:48AM
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The link below are the recommendations of the US Department of Energy for cost effective installations.

(These may or may not exceed state or local requirements.)

In my location, I'd fill the stud spaces with fiber insulation, as R5-R10 boards fall below the required Code minimum.

Here is a link that might be useful: Cost Effective Insulation levels

    Bookmark   February 16, 2008 at 12:30PM
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