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Old 08-09-2012, 04:35 PM   #1
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crawl space insulation


Can I improve insulation of floor of 4 seasons room with rigid foam insulation added to bottom of joists? Joists are insulated with fiberglass batts and 6 mil film is on ground covered with gravel. No foundation. 12x16 room supported on piers. Thank you.

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Old 08-09-2012, 05:01 PM   #2
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crawl space insulation


The PIR / PUR rigid boards are far more efficient as insulants than fibreglass batts. Cut the boards to fit tightly between the joists and then drive a few nails in at an angle below in the sides of the joists to stop the boards dropping down.

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Old 08-10-2012, 05:40 PM   #3
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crawl space insulation


If no vinyl above, may need to cover f.b. for code: http://www.buildingscience.com/docum...n-crawlspaces/

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Old 08-10-2012, 11:30 PM   #4
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crawl space insulation


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Originally Posted by cecker View Post
Can I improve insulation of floor of 4 seasons room with rigid foam insulation added to bottom of joists? Joists are insulated with fiberglass batts and 6 mil film is on ground covered with gravel. No foundation. 12x16 room supported on piers. Thank you.
If you REALLY want to get this right and STOP all moisture problems/mold possibilities and get very HIGH R values, rip out ALL insul and get an insulation spray foam company in a spray foam all joist bays.

The killer on crawl spaces goes like this. Of ANY standard fiberglass insulation gets 5% of moisture in it, then that insul loses 90% of its insul intended values,
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Old 08-11-2012, 02:40 AM   #5
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crawl space insulation


If you decide to keep the fg insulation and nail up rigid foam, tape the edges of the foam and/or goo in between sheets. Closed cell spray foam is the best, bus spendy, if the joists are completely covered.
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