Rim-joist Insulation - Spray Or Sheet Foam? - Insulation - Page 2 - DIY Chatroom Home Improvement Forum

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Old 01-15-2012, 08:43 AM   #16
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Just a note.... in a basement the air flow moves both from the exterior to the interior in the summer and from the interior to the exterior in the winter. So a vapor barrier (spray foam top and bottom edges of rim joist prior to batt installation) will trap moisture in the winter. Thus.... no fiberglass!
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Old 01-15-2012, 09:18 AM   #17
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Thanks for the reply Bob.
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Old 01-17-2012, 01:55 PM   #18
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I was looking at doing this to my basement recently- good info here.
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Old 01-17-2012, 04:38 PM   #19
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I would not be so sure Option 2 is easier. I recently found air leaking where 4 inlet/ehaust pipes (water heater and furnace) ran through. The spray foam did not have enough adhesion and/or mechanical strength and would pull off just by gravity. (That never happens to Mike Holmes) I managed to get the job done by damming up the area to be insulated, but I would not look forward to doing a whole house like that.
OK, I used the house brand foam of a big box store. If you bought the PU foam in two tanks, that might be better stuff. But I would tend to agree with the fellows that suggested XPS foam boards.

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Old 01-30-2012, 08:44 AM   #20
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Originally Posted by Bob Mariani

Because any profession with building science knowledge will know that this will only trap moisture making the fiberglass ineffective and for mold to grow. Rim joists need to be air sealed and insulated to the same R-value your local codes require for the exterior walls. R19 in my area. Here is how I do rim joists http://www.homedoctorofamerica.com/rim-joists.

Your first solution (flash an batt works fine. Easy to use Roxul batt and spray foam. Or use polyicocyanurate foam board. Spray foam is much easier and is the only method I use.
Following this thread. Good info. One question, what if you have electric wires running in this area?
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