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Continuous vapor barrier sealed and covering basement floor & walls?

Continuous vapor barrier sealed and covering basement floor & walls?

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  #1  
Old 10-27-19, 08:41 PM
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Question Continuous vapor barrier sealed and covering basement floor & walls?

New construction in Chicago - Should my 10 mil poly vapor barrier cover my basement slab and run up all walls to the floor joists; all taped and seal to create one continuous vapor barrier membrane? The floor would be slab + 10 mil poly + 1/2" foam board + 5/8" sub-floor + waterproof vinyl planks. The walls would be concrete wall + 1" foam board + 3.5" R-15 mineral wool + 10 mil poly vapor barrier + 5/8" drywall + latex paint. All interior walls would be built on top of the sub-floor and there is a 9' ceiling that will be insulated with mineral wool and have 5/8" drywall.

Looking for thoughts on this approach and any other ideas. Thanks!!
 
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Old 10-27-19, 08:52 PM
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Short answer, no. Vapor barriers below grade are a bad idea. What you are describing would only be done in an unfinished, unframed, conditioned crawl space.
 
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Old 10-28-19, 03:30 AM
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You've created a massive water trap, moisture, not water needs to be able to flow, putting up the plastic traps the moisture, turning it into water which has nowhere to go!
 
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Old 10-28-19, 02:48 PM
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I see no problem with the way you want to do the walls.
You are in Chicago so it gets cold therefore you need a vapor barrier on the inside walls under the drywall.

Not sure about the floor. I think something like Drycore would be a better option.
It will not get that cold so you really do not need a vapor barrier, better that it breathes.

The only caution I have is that I hate doing this on a new foundation as you cannot be sure that it will not leak.
But if you are confident that the outside of the foundation is waterproof I cannot see a problem.
 
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Old 10-28-19, 05:06 PM
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The latex paint on your drywall is a class III vapor retarder and is all you need. You don't use vapor barriers on framing below grade because below grade the wall has to be able to dry to the inside since it can't dry to the outside.
 
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Old 10-28-19, 06:07 PM
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You are in Chicago so it gets cold therefore you need a vapor barrier on the inside walls under the drywall.
I]Vapor Barriers Are a Good Thing, Right? Builders once installed polyethylene plastic on the inside of exterior walls to stop the flow of moisture into call cavities in the winter. Now building scientists question the practice.[/I]

Old school thought was seal it up, but the only place where barriers are advised today is under a slab.
 
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Old 10-28-19, 06:54 PM
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As long as you don't have a liquid water leak the amount of moisture vapor passing through the concrete is very minimal and easily added to the normal interior heating and cooling. That vapor only becomes a problem when you block it (a vapor barrier) and allow it to accumulate.

Bud
 
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