Old 03-12-00, 12:00 AM
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when insulating 2x4 sidewalls why not use the 5-1/2" thick batts to achieve a higher "R" value?
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Old 03-12-00, 01:32 AM
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You only have 3.5" of insulation space in a 2X4 wall, and compacting insulation defeats its purpose. You will not gain any r-value cramming the 5.5" in a 3.5" space, just extra cost. Should use batts made for depth being insulated. Also, recommend using plastic sheeting over walls after installation for better moisture barrier, even if insulation has backing.Good Luck!
Old 03-12-00, 04:11 PM
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OldGuy is correct about compressing the insulation. Insulation works by "loft" (trapped air). Compressing it reduces loft, thus reducing R-value.

Instead of using R-11 or R-19, you can use R-13 inside a 3 1/2" wall. Using a vapor barrier doesn't necessarily increase R-value, but does help keep cold out and heat in.

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