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Old 01-09-2014, 11:34 AM   #1
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Garage ceiling/room above


New homeowner here. I have an attached garage with master bedroom above. I knew this would be an issue, but want some advice before I spend a dime. The garage is fully drywalled and in poking some test hole I'm seeing r-11 or r-13, faced toward the subfloor and in great condition but no vapor barrier. The drywall on the ceiling was covered by regular styrofoam panels (red flag!). So after this deep freeze in PA, I need to expedite this project. The ceiling is coming down. The question is - should I pay up for spray foam, or keep the batts and glue up 2in ISO foil backed boards, tape, and seal around any gaps?? And does foil backed ISO need drywalled for fire protection?

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Old 01-09-2014, 11:58 AM   #2
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Garage ceiling/room above


An attached garage needs 5/8 fire code drywall.

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Old 01-09-2014, 11:40 PM   #3
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I agree with Joe, need the Type X and Fig. 7; http://www.buildingscience.com/docum...n-crawlspaces/

And: http://www.buildingscience.com/docum...al-performance

From R-19-----R-30, read Footnote "g";http://energycode.pnl.gov/EnergyCode...e=Pennsylvania

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Old 01-10-2014, 07:28 AM   #4
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Garage ceiling/room above


Awesome stuff! Thanks! On the 2nd link I have Fig 5: Compliant & Cold. I'm shooting for Fig 2, or Fig 1 if I have the time & effort.
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Old 01-16-2014, 11:19 PM   #5
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Garage ceiling/room above


Insulated ceilings minimize heat passing through as it rises, but insulating an unheated garage ceiling also may help reduce the chilling effect of cold air circulating underfoot. Some newer garages have insulated ceilings; older ones may not. If the garage ceiling is finished with plywood or drywall, chances are better that insulation exists. To check, you’ll need to cut a hole in the drywall and look inside with a flashlight, or remove a sheet of plywood. If the ceiling is not finished and you see no insulation, or if cutting into the drywall or removing plywood reveals a bare cavity, new insulation may help break the chill. Insulating a tall garage ceiling often is better left to professionals who can add insulation batts, blow in loose insulation or spray in foam. The insulated ceiling should be covered with drywall or plywood afterward. While you're in the garage, address drafts that may infiltrate around the garage door.
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Old 03-09-2014, 10:48 PM   #6
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Gary (or anyone else), in the 2nd link the first two figures show what I want to achieve. Right now I have fiberglass insulation, drywall, then regular styrofoam glued to the drywall (previous owners idea). Do you believe I can achieve the same results of Fig 1 or 2 by simply taking styrofoam out and properly installing rigid foam on top, then drywall again as a fire retardant?? Or would I need to take down the existing drywall??
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Old 03-10-2014, 09:11 AM   #7
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Do you have access to the knee wall? In my bonus room, they slid R19 (6" thick) into the 2x10 joists. My plan is to blow cellulose into that cavity to close the air gap. Can you check and see if they have enough insulation in that section? Also, if there is the air gap between the floor and the insulation, all of the foam board in the world on the garage side won't help because the cold are of the attic/knee wall will be getting under your floor.

Jumping into the knee wall will give you a plethora of information.

You mentioned that there wasn't a vapor barrier, but the vapor barrier would be against the floor, not the drywall facing the garage.
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Old 03-11-2014, 12:53 AM   #8
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Fig. 7 in the first link I left shows over a garage is similar to a crawlspace. IMO, the layer of drywall between FB would not effect it much (the key is air seal all joints/holes/gaps). You are required to cover the FB with drywall- 5/8" Type X because of the living space above; "e. Type X gypsum board for garage ceilings beneath habitable rooms shall be installed perpendicular to the ceiling framing and shall be fastened at maximum 6 inches o.c. by minimum 17/8 inches 6d coated nails or equivalent drywall screws." From; http://publicecodes.cyberregs.com/ic...002_par010.htm
Always link where it is from or it is plagiarism...MC Plywood is unacceptable.

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Old 03-11-2014, 11:55 AM   #9
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Thank you Gary!! I now have my gameplay for the garage ceiling thanks to your assistance. Now all I need is the western PA weather to get warmer...
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Old 03-11-2014, 11:56 AM   #10
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*gameplan
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Old 06-05-2014, 10:50 AM   #11
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Ok I'm going forth with my project soon and I have a question - since I have proper rolled insulation in between the joists of the garage ceiling and I'm really trying to achieve a proper seal, what thickness of rigid foam would be best?? I'm conflicted between the .25" fanfold since it's cheap or adding even more r-value and doing 1".
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Old 06-06-2014, 07:22 AM   #12
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Go 1".

Fan fold won't hold up and is typically micro perforated.
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Old 06-06-2014, 07:52 AM   #13
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Thanks! I see on Lowes site now they list their fanfold as being perforated to allow moisture.
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Old 06-06-2014, 09:23 AM   #14
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You compressive strength of fanfold at that thickness is not good enough to screw drywall through and hang it from. Stick with a 1 inch XPS foam instead.

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