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The Dogger 12-09-2012 09:30 AM

Vapor Barrier ?
Hello all, just starting to finish my basement and joined the site today.

Quick background: I have an inground basement (poured concrete floor), with a drain tile/sump pump system already installed. I have not had any water issues in the basement since I have lived here for the last 5 years (house is 10yrs old). The builders at the time of construction did build 2x4 walls with insulation around the outside walls of my basement and I have found that they installed a standard plastic sheet vapor barrier between the concrete block foundation and the outside of the 2x4 wall. They also installed another vapor barrier (plastic sheet again) on the inside of the 2x4 wall.

After having a few contractors over to assess a seperate issue (support pole moving) in my house, they have recommended to me that this double sided vapor barrier was a thing they did for a few years in my area, but is actually not a great idea as it creates a "zip lock" bag effect around the insulation/2x4 wall - which in turn could get mold if there was a moisture issue in the basement.

I will be finishing the walls myself, and the last contractor recommended to me that I either put slits in the vapor barrier between every 2x4 or actually completely remove it.

Can anyone advise to me what I should do here? I have a hard time removing a vapor barrier that was purposely put there for a reason but then again I know nothing about this topic and need help.

Gary in WA 12-09-2012 04:01 PM

Welcome to the forums! There are many threads on basements from using the white "search box" at the top of every page. This will get you started on the "diaper" insulation system you now have and don't want;

Pick your choice, not poly; pp.8, 26-29, 47-51, summary pp.69;

The slits do nothing as a vapor barrier is area weighed;


The Dogger 12-09-2012 05:59 PM

OK, I just skimmed over that buildingscience article and I'm already officially overwhelmed. From what I read there I should rip down every wall along the outside of my basement and re-build it according to one of their recommended ways.

I understand having the diaper effect is bad, but will I be OK if I just remove the inner-side poly and put sheetrock up?

Gary in WA 12-11-2012 10:50 PM

You could try it that way, if you want. The foamboard against the concrete with a drain interior warms the cavity to prevent condensation, fig. 15;

Without the foam and just poly sheeting on the concrete, with f.g. batts;


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