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Rigid insulation behind drywall

MMitrano | Posted in Construction Techniques on March 9, 2009 06:22am

Hi, all. This question is for people who’ve had experience putting right insulation between framing and drywall.

I am finishing my attic and need more R than I can get with insulation between the rafters. I am considering different combinations of added framing and material that will get me what I need. One possibility involves putting 1/2″ or 1″ rigid (polyisocyanurate) insulation behind the drywall. This will isolate the framing from the drywall thermally. I have put 1/2″ rigid insulation behind drywall on walls with no problem.

On a sloping (10:12) ceiling with 1″ insulation, I will need 2 1/2″ drywall screws. I am worried about the assembly slipping “downhill” over time resulting in cracking. Has anyone done this on a sloping ceiling? If so, did you have any problems? Thanks!

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  1. fingersandtoes | Mar 09, 2009 07:36am | #1

    I've done two layers of drywall, and drywall on resilient channels with no problem. I can't see that 1/2" rigid insulation would be much different.

    1. User avater
      xxPaulCPxx | Mar 09, 2009 08:58am | #2

      It won't, there is too much friction invloved for it to slip down.

      If you are really worried, you can use a foam glue on the rafters and the panels to keep them extra stuck in place.

      Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!

      Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

  2. cargin | Mar 09, 2009 02:21pm | #3

    Mitrano

    I have 2" XPS on 2 sloped ceilings over plaster.

    I then furred out the XPS with 1x3s. It takes a 4 3/4" screw to hit framing. But then you have a nice surface to screw drywall on.

    No problems with slipping.

    In this age of rising prices and the need for superinsulating our homes I opted for deeper styrofoam.

    Rich

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