Vapor barrier on ceilings?

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Old 07-15-04, 07:36 PM
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Vapor barrier on ceilings?

Please help me out here. I have a 24'x24' garage with trusses on 24 centers. I want to insulate the ceiling but will probally not put up drywall right away.

I was thinking of adding a 4 mill vapor barrier over this insulation. I have been told on a ceiling yes and no?

What is right? Does it matter?

Thank you
 
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Old 07-15-04, 07:57 PM
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Vapor Barrier Depends

Whether or not you use a vapor barrier depends upon what is above the garage ceiling.

If you have an attached garage and there is living space above it, then insulation should have a vapor retarder and it should be place up against the floor of the living space above.

This means that if you use kraft faced insulation, the vapor retarder goes "up" against the underside of the floor.

The key is that vapor retarders go toward the heated side of the structure.

Put another way, vapor retarders go toward the living side space of the joists or studs.

If the garage is attached or detached, unheated and there is no living space above the garage, no vapor retarder is required since there will be no significant heating or cooling differential between the garage and the garage attic to worry about 'vapor'.
 
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Old 07-15-04, 08:07 PM
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Most States require any insulation in a garage be covered with a fire rated material. I strongly recommend you check with your local authorities for their building codes.
 
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Old 07-16-04, 12:08 PM
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Thanks very much! The garage is not attached.
 
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Old 07-16-04, 12:48 PM
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Wink

Still check code for there . And yes I would for sure put up a 6 mil poly there on the celing after the insulation is up. to help hold it with 24" on center and to keep any fiberglass dust from comeing down on you.


ED
 
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