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Old 11-15-2012, 03:34 PM   #1
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Insulating a Garage Ceiling

Hi There Y'all

I am new to this forum. I am seeking a way to insulate my garage ceiling and I appreciate any input that you might have.

But first a little backstory.

We have a split level house, bedrooms over garage(non-climate controlled).

House built in the 1960's. We moved in two years ago

Garage celing was insulated and then finished with drywall. I began to notice that the paint on the drywall bubbling in some areas. (uh-oh)

Some exploratory pokes in to the sheetrock revealed extensive severe soaking and mold of the insulation batts which were attached paper vapor barrier down towards the garage.

My theory holds that this garage which is non climate controlled, gets steamy and hot in the summer time. for forty years that humidity has been rising up and meeting with the living space area which was climate controlled and cool in the summer time and that all that humidity was just sticking right into that insulation.

so we are getting ready to rip out all the drywall and saturated insulation and the tar paper which was below the subfloor above. So hopefully we wont have to replace the second floor subfloor. And now I am wondering what to do, to insulate effectively and to prevent this from ever happening in the future.

Oh yes, I am also concerned about using insulation products which may pose an indoor air quality concern such as spray foam and or ridgid board insulation. There is a lot of scuttlebut over whether these are safe for humans indoor, but I want to err on the side of caution and skip them.

So I have so many questions?

Vapor Barrier? If so, which side of the insulation? Rock wool? Put drywall up again?

Any help would be wonderful.

Thanks so much


Curl is offline   Reply With Quote
Old 11-15-2012, 10:04 PM   #2
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Is this area just used as a garage anyway? Or is this room used for another purpose simultaneously?

At any rate, first solve the water leak issue by removing old/damaged sheet rock. Once this is addressed, then you should just put back sheetrock to cover the opening caused by the repair of the water issue mentioned.

I was trying to look for a specific question from your post, but since you left it generally stated, I hope you don't mind the general response.


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Old 11-15-2012, 11:09 PM   #3
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Sure sounds like there a leak someplace not just rising moisture for it to have been that wet.
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Old 11-16-2012, 08:42 AM   #4
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Roxul would be a good choice.

My son has exact same design, garage in basement with bedrooms over. Going to tear out drywall and search craigs list for cheap styrofoam and FILL it as well as can be, finishing cracks with spray foam in a can,,,'Great Stuff',,,then drywalling over it all. Nothing wrong with styrofoam if its covered by drywall in case of fire, no fuming. best R value you can get.

While we are in there will replace ANY flex furnace ducts we find with solid pipe, tape and seal ALL joints so leakage isnt an issue and I am sure the bedrooms will be very much warmer. Will put plastic over joists before drywall.

Key to the NEED for this is I parked my car in there. With the door open If my car was backed in,,,the fumes were VERY strong in bedrooms when car was started and moved outside as fast as possible. IF it was well insulated and sealed could not happen that fast.

While we are at it if we can find any extra Styrofoam the outside block wall gets at least 2" with drywall over. Then basement room with unfinished walls same thing. Its COLD in there now,,,,cant hurt much
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Old 11-17-2012, 07:15 PM   #5
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You didn't say where you live, but in northern areas the vapor barrier is always installed on warm side.
The moisture that you have encountered is from moisture laden household air penetrating the insulation and when it reaches the cold vapor barrier, the moisture condenses on the plastic.
When you remove the moldy insulation, staple 6 mil plastic onto the subfloor.
Then, as previously mentioned, insulate with R20 Roxul batt insulation.
New drywall can then be reinstalled.
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