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pete0403 01-23-2012 03:50 PM

Opinions on wall system please

I'm looking to get some opinions on finishing a room in my basement. This is going to be a room for dog grooming. The room is 1/2 underground, has a cement wall half way up on 2 sides and a 2x4 wall the rest of the way (exterior sheathing is lined with tar paper).

Not pictured in the (crude) drawings is capillary breaks under the XPS and bottom plate of the new wall as well as foam board, caulk, and insulation around the rim joists. All insulation will be roxul and drywall mold-resistant. New wall would be blu-wood with probably a PT bottom plate.

Please be critical of any errors I'm making in these ideas so I know. I Live in ON.

Option A:
It would be nice to have a built-in ledge on two walls but I'd lose a bit of R-value with the 4" exterior wall.

Option B:
Better R-value...the new wall would be insulated as would the space between the VB and new wall.

Option C:
Same as B except 2"XPS instead of poly VB.

mae-ling 01-23-2012 04:02 PM

NO poly vapor barrier.
Building science has lots of good info. Look around there site.

Here is a previous thread on this topic. Good reading.

pete0403 01-23-2012 04:22 PM

I thought it was just no poly vb for concrete...the upper 1/2 of the wall is a standard 2x4 wall.

mae-ling 01-23-2012 04:32 PM

You are correct. Sorry confused the colors in your drawing.
Do option A with modification. build top part out to be flush with bottom part. put in minimun r20 or more up to the thickness of the new wall. Poly it properly and seal it to the concrete.

pete0403 01-23-2012 06:10 PM

Thanks. So basically option B is the way to go? Too bad I was liking the idea of the little ledge.

Is there any problem with insulation in front and behind the VB?

pete0403 01-25-2012 11:29 AM


mae-ling 01-25-2012 05:31 PM

On the wood wall you want vapor barrier on the warm side of the wall, No Vapor barrier on the concrete.

If you want the ledge put 2" strips on each stud, and bottom plate. Then use r20 insulation. seal the poly to the bottom of the wood wall and concrete joint.

So basically A with 2" strips added to studs

pete0403 01-26-2012 12:19 PM

Good idea, thanks.

pete0403 04-11-2012 03:10 PM

I have decided to go with option A so I have a ledge built into the wall around the outside walls of the room. It will be a handy thing to have for bottles, etc and it will be about 6-8" over the top of the counter in some spots leaving enough room for outlets (no sink, just countertop). This is a dog grooming shop.

The question is, (looking in post #1, option A). How is the best way to tie the two walls in? Place a 2x4 flat side against the existing (brown) wall at the height of the new wall and then toenail the top plate of the new wall in from above?

With the new wall against the foamboard, there will be a 1/2" gap between the top 2x4 plate and the existing wall...herein lies my problem. I'd like to avoid ripping 2x6's.


Mohonri 04-12-2012 04:32 PM

To tie the top of the half-wall into the bottom of the existing wall, you'll need to put in short pieces of 2x4, laid flat, with the grain perpendicular to the wall.

One question you asked earlier was about putting VB in the middle of the insulation. The general rule is to put the VB as far towards the warm side as you can. That way, the "cold" side of the VB is as close as possible to ambient warm-side temperature, and so the water vapor is less likely to condense. The closer the VB is to the cold side, the colder that moist interior air will be when it hits the VB, and the more likely it will be that you get water in your walls.

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