Basement 1/2 Wall Framing Help

[RetroActv]

I'm working on finishing my basement. Kind of stuck on how to best frame the 1/2 wall (house has a lookout basement). I started one section, but before I go too far I thought I'd seek advice.

I've attached a picture for reference. For the section I did, I had the wall go as high as the concrete ledge. What's the best way to handle the ledge? Should I put some XPS down to insulate it, or cap it with a 2x cut to fit from the back of the ledge (tying it into the 2x6 wall) out to the edge of the framed wall? Should I lay some soldiers 4 feet apart, and use insulation in-between? Just a bit stuck on the best approach. I considered framing all the way up to eliminate the ledge, but for various reasons decided to keep the ledge.

My thought once it's framed and ready to be finished, is to use either MDF or another material to have the bottom window casing tie into the ledge itself, since there doesn't seem to be space to use any sort of trim on the bottom, give the window's proximity to the ledge. But, I'm open for ideas.

Height from floor to the concrete ledge is about 37".

Thanks.

 

[Dana]

Polyiso would have been a much greener solution here, but if you have enough 1.5" XPS left over from the wall insulation to cover both the top of the concrete ledge right out over the top of your interior-side studwall would be fine. I'm assuming you'll be installing batts in the studwall (?).

MDF long screwed/nailed through the foam would be fine.

In your case the top plate of the studwall is at the same height as the ledge, unlike the picture below. The principle is the same, except that your ledge-foam would extend all the way to the drywall (or MDF).

XPS is blown with HFCs now banned for the application under the Kigali Amendment to the Montreal Protocol due to their extremely high global warming potential. The HFCs give a temporary performance boost to the foam, but you'll note in the fine print that it is only warrnateed to 90% of it's labeled R-value over time. That 1.5", R7.5 foam should be considered no better than R6.75 a design point of view, and even that may not be conservative enough. Over enough decades the performance will drop to that of EPS of similar density, which would be R6.3 @ 1.5". XPS is perhaps the least-green of all commonly used insulating materials in the US, primarily due to the HFC blowing agents, but also the polymer type and polymer weight per R.

If insulating the cavities with fiber insulation make the drywall or MDF air-tight, and paint it with a "vapor barrier latex" primer, which lowers the vapor permeance enough to avoid wintertime moisture build up, but still sufficiently vapor open that ground moisture can dry toward the room rather than create a mold farm in the stud bays.