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So I have two questions that I was hoping I could get some clarification on. First, here's the details on my project...

I am insulating a basement room. I have already glued and seals 1" rigid foam to the concrete foundation. I then framed a wall 1/4" off of the rigid foam. (I also used rigid foam and roxul in rim joists) I am in the northeast and this area of the basement has never gotten water. Lastly I installed roxul in between the studs. I am about to close it up but had these questions.


1) There seems to be so many varying opinions on when to use poly on studs over between drywall with this method. Should I? Will this create mold trapped inside? Any insight?

2) If I need to use poly, do I also apply poly to the interior walls (the walls in the middle of the basement, not perpendicular to the foundation) of the basement room? Or just the exterior walls?

Thanks!
 

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The frequent use of poly got started by mistake many years ago and due to it creating more problems than it eliminates the experts are now working in reverse to limit its use. It is this change in direction that has fostered the widely varying opinions and even code requirements. Some basics.
Moisture is still passing through your foundation, that is the nature of concrete. The tar on the outside may slow it somewhat but moisture can move vertically over 100' so it has no problem soaking up from below the footings and slab and into the walls. The good news is, it does so very slowly and if allowed to pass it can be handled on the inside very easily.

The problem arises when we block it with a vapor barrier. When it can no longer pass to the air it accumulates until it matches the moisture in the soil from where it came. One of the modern lines of thinking is to eliminate the vapor barrier and use nothing more restrictive than a vapor diffusion retarder and the 1" blue or pink foam board (unfaced) is a retarder. Hard to believe moisture passes through it but in a vapor form it does.

Th add more confusion, they changed their minds AGAIN. Well not completely, but the only foam board rated to be left exposed is foil faced Dow Thermax and it is certainly a vapor barrier. So, they tested and said, if the concrete behind the foil facing gets wet and stays wet, not a problem. However, they did not say we should be using a vapor barrier just that it may not be bad when we use this one product. Confused? Join the crowd. My opinion remains to omit the vapor barrier unless required by code (some still need to see it). Allowing a small (tiny) amount of moisture to dry to the inside ensures it will not be accumulating behind any vapor barrier.

I'll stop there and do read the link christoff posted, they have others as well.

Bud
I type slow,
No vapor barrier anywhere is fine especially on interior walls.
 

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Discussion Starter #5
The frequent use of poly got started by mistake many years ago and due to it creating more problems than it eliminates the experts are now working in reverse to limit its use. It is this change in direction that has fostered the widely varying opinions and even code requirements. Some basics.
Moisture is still passing through your foundation, that is the nature of concrete. The tar on the outside may slow it somewhat but moisture can move vertically over 100' so it has no problem soaking up from below the footings and slab and into the walls. The good news is, it does so very slowly and if allowed to pass it can be handled on the inside very easily.

The problem arises when we block it with a vapor barrier. When it can no longer pass to the air it accumulates until it matches the moisture in the soil from where it came. One of the modern lines of thinking is to eliminate the vapor barrier and use nothing more restrictive than a vapor diffusion retarder and the 1" blue or pink foam board (unfaced) is a retarder. Hard to believe moisture passes through it but in a vapor form it does.

Th add more confusion, they changed their minds AGAIN. Well not completely, but the only foam board rated to be left exposed is foil faced Dow Thermax and it is certainly a vapor barrier. So, they tested and said, if the concrete behind the foil facing gets wet and stays wet, not a problem. However, they did not say we should be using a vapor barrier just that it may not be bad when we use this one product. Confused? Join the crowd. My opinion remains to omit the vapor barrier unless required by code (some still need to see it). Allowing a small (tiny) amount of moisture to dry to the inside ensures it will not be accumulating behind any vapor barrier.

I'll stop there and do read the link christoff posted, they have others as well.

Bud
I type slow,
No vapor barrier anywhere is fine especially on interior walls.


Thanks for the information!
 
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