DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Insulation and Radiant Barriers > Vapour barrier over drywall?

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Old 09-23-2013, 12:24 PM  
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Default Vapour barrier over drywall?

Up on the high ceiling there is:

1) New dry wall
2) Styrofoam 2"
3) Old gypsum board somewhat moldy, not sure to what extent
4) some tin foil 1950's?
4) Moor vents (new)
5) roof with airflow to outside vents.

I was thinking of covering it all with poly 6mm, then finish it. Main reason is to keep the mold out and save me from tearing it out and rebuilding.

Good idea, or could it make it worse?

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Old 09-23-2013, 04:55 PM  
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I would think it would make it worse if the ceiling can't breath.

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Old 09-24-2013, 08:29 PM  
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This is all dependent on your climate. In cold climates, you do not want water vapor to be trapped in a cold area since it will condense out. Around us in our cold WI climate, a few homes were built that had plastic under the siding - this was such a disaster that these homes had to be torn down. So in a cold climate, the moisture barrier goes just under the interior drywall. This keeps the water vapor out of the cold region, so it stays vapor rather than water.

The styrofoam, if sealed well on the edges, is a vapor barrier and it would prevent moisture from being trapped. If, however, the cracks are not sealed, moisture would get through and then condense on the old sheetrock underneath - this could be the cause of the mold you see. Not good - you may want to clean up or remove that drywall and reinstall or replace the styrofoam. Then put a vapor barrier over the styrofoam and seal up the edges of the styrofoam. I am assuming you live in cold climate.
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Last edited by Drywallinfo; 09-24-2013 at 08:33 PM.
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Old 09-27-2013, 04:56 PM  
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Mold can be corrected or prevented by using moisture resistant sheet rock, proper ventilation and high gloss paint. Adding foam is only good on the opposite side of the finished side of the sheet rock.
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Old 09-28-2013, 12:05 PM  
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I've never heard of mold being corrected unless it just once getting wet. Looks like the flat ceiling is okay just the slope. There is bunch of old celuose insulation up there along with a birds nest. Not a fun job. What i find is old piece of half rotten reclaimed lumber used in places, but the basic framing seems to be good lumber.

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