Vapor Barrier On Basement Pony Wall - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 01-06-2011, 12:03 PM   #1
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vapor barrier on basement pony wall


I'm finishing a section of my basement that has a 4' concrete pony wall (below grade foundation) with 4' framing set on top. The framing is set back on the top of the foundation by about 4". I'm planning a new wall flush with the foundation to a new top plate on the floor joists above, no ledge. My question is about the vapor barrier.

The concrete wall will be insulated with EPS then fiberglass in the new wall against the EPS rigid board, so the EPS will act as a vapor barrier against the cold wet concrete, but what should I use as a vapor barrier on the framing above the foundation?

If I continue the fb in the new wall to the ceiling, do I use 6 mil on the warm side of fb on the top half of the new wall then tuck it behind the EPS where it meets the foundation? Doesn't seem right working the 6mil around all the studs, lots of holes. I insulate only within the existing framing on top of the foundation, put 6 mil on the warm side of that, and tuck into the EPS where it meets the foundation? This would leave air gaps between studs of the new wall and behind, also doesn't seem right. I read somewhere air gaps in basement walls promote air flow increasing moisture movement and drafts, maybe that's called convection.

I'd like to stuff the entire cavity (created with the new framing above the pony wall) with fiberglass (or something else, suggestions?) but can't find a definitive answer on where to put the vapor barrier.

I live in Vancouver Canada, the house was built in 1962.

Thanks eh,



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Old 01-11-2011, 03:12 AM   #2
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I have the same scenario in my basement (Ontario house built in '66) and would like to bump this to the top for more views.

Is the framing on top of the pony wall an interior wall?


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Old 01-11-2011, 02:27 PM   #3
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Hi Pete,

The framing on the pony wall is not an interior wall, it's 2x6 studs on the exterior rim of the foundation.

Not sure you'd need insulation or vapor barrier on an interior wall, guess that depends on what the other side of the wall is used for though...

So, far as I can tell, my best bet is a vapor retarder above the pony wall, such as kraft faced insulation. No 6 mil at all. Rigid board against the foundation, well sealed, then faced fiberglass batting in the existing framing above, (paper facing warm side of fb). I'll pack the new framing with fb as well without a barrier so any vapor that gets in can dry to the exterior or interior.

I found a lot of good info at though I think this is a consulting firm that tests in labs, not the real world, for what it's worth. is good too.

Haven't started the job yet though, so if anyone has any feedback on my "kraft faced fb as vapor retarder" solution, be glad to hear it.


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Old 02-13-2011, 08:07 AM   #4
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Basement Insulation


With respect to insulating your basement - or anything else for that matter, small gaps or penetrations and incompletely sealed transitions etc., in your vapor barrier create enormous problems by concentrating moisture movement through them. What you need is a single, monolithic barrier to moisture movement.

While it is more expensive, spray foam insulation, when properly applied is the very best solution - it creates a thermal barrier, an air barrier and a recognized vapor barrier in a single application. It has a higher R value than any other material on the market and because it locks out moisture, it will eliminate that slight damp and occasional musty smell that basements can sometimes take on.

There is a good local spray foam blog if you are interested in more on spray foam in the Fraser Valley and Vancouver.

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