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Plastic Vapor barrier in attic prior to blown insulation

Plastic Vapor barrier in attic prior to blown insulation

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  #1  
Old 01-26-14, 09:25 AM
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Plastic Vapor barrier in attic prior to blown insulation

I am going to blow insulation into my attic and noticed one video where the people put down plastic over the floor studs as a vapor barrier prior to blowing the insulation.

I have only seen this in 1 video of about 10, should I do this ? is it needed or provide benefit?

Thanks
 
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  #2  
Old 01-26-14, 10:09 AM
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In extremely cold climates, which I think you qualify, a vapor barrier or class I vapor retarder is recommended on the warm side of the insulation. But installing one properly after the sheetrock is up is difficult if not impossible. As al alternative, a good layer of paint can do part of the job and air sealing the house to attic even more so. Air leaks transport much more moisture than vapor diffusion, so recessed lights, electrical boxes, plumbing and wire penetrations and a chimney chase can be worthwhile projects.

Also, make sure bath and kitchen fans are vented fully to the outside, not just into or below a soffit.

Here is a link on vapor barriers: Vapor Barriers or Vapor Diffusion Retarders | Department of Energy

Bud
 
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Old 01-26-14, 12:16 PM
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If I understand you correctly, you are wanting to put a poly vapor barrier over the top of your ceiling joists, on top of any existing insulation, and then add more insulation on top of that? IMO that would be a bad idea, as moisture could possibly condense inside the insulation that is below the poly... especially on the colder perimeters of the home.
 
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