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Old 02-21-2011, 12:37 PM   #1
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Air-gap Between rigid floor insulation & subfloor


I am building an addition in what used to be the ground level attached garage.

I've researched all about proper insulation and vapor barriers for the concrete floor. I know all about the products that are available. I was actually going to install myself, but ran out of time and had to hire someone to do it.

My problem is trying to get my contractor to deviate from his way, his "old school" way. The concrete floor has a slope in it, so he is building a leveled platform subfloor over it. He was just going to use plastic sheet for barrier, and no insulation. I insisted on at least putting rigid insulation over that, so he's going to drop in a layer of it in.

My question is, since there is a slope, this will create an air gap at the lower end of the slope between the subfloor and insulation. Will this air gap negate the effects of insulation?

Also, there is a floor drain in the concrete for the garage that is being covered. Is it necessary to seal that up?


Last edited by acerunner; 02-21-2011 at 12:47 PM.
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Old 02-21-2011, 08:05 PM   #2
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Air-gap Between rigid floor insulation & subfloor


"My question is, since there is a slope, this will create an air gap at the lower end of the slope between the subfloor and insulation. Will this air gap negate the effects of insulation?" ----- yep; The "biggest loser" in fiberglass insulation....

Gary

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Old 02-22-2011, 04:03 AM   #3
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Air-gap Between rigid floor insulation & subfloor


d it. that's what i figured.
any suggestions on a remedy for this situation?

Last edited by Gary in WA; 02-23-2011 at 04:02 PM. Reason: keep our "G" rating
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Old 02-22-2011, 09:41 AM   #4
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Air-gap Between rigid floor insulation & subfloor


glue to the underside of the joists and prop it up as you go. Fill between joists with fiberglass
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Old 02-22-2011, 01:36 PM   #5
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Air-gap Between rigid floor insulation & subfloor


K thanks. The plastics sheets need to be taped our glued together also right? I'm pretty certain im right bout that. Contractor insist simply overlapping the sheets is enough.
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Old 02-23-2011, 04:33 PM   #6
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Air-gap Between rigid floor insulation & subfloor


I would not use plastic (impermeable) sheeting. Either equalize the vapor pressure using FL or Fig.#3; http://www.buildingscience.com/docum...ms?full_view=1
OR coat with a product as in fig.#2 letting it dry to the inside room above.Summer time problems.

Gary

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