Attn: Dana, Clever Solution

[dlarrivee]

I'm hoping you can lead me in the right direction here.

I have a 2x4 stud wall, on my split level entry landing... I removed the drywall to fix a crack, the original board had a joint exactly at the same height as the framing transition for the header over the door...

I have stucco on the outside that isn't going anywhere any time soon.

I plan to spray 3" of 2lb. density foam in the stud bays, but I'm hoping you can point me in the right direction as far as killing the thermal bridging at the header and each stud?

I can spray within 1/2" tolerance of the face of the studs just fine.

I would like a double stud wall, with 1" space, but don't have enough room for that with the stair landing. I could afford to lose about 2"...

[dlarrivee]

Okay so tell me if I'm crazy.

I get some 1.5" thick XPS and rip it to 1.5" wide strips... as well as some 1/2" thick plywood.

Essentially a foam and plywood furring strip.

I create a sandwich at each stud face, and use 2" thick XPS at the header.

I suppose another option would be an 1 5/8" steel stud wall in front of the existing wall, spaced off the existing framing to allow a 2x6 rough in door...

Am I over thinking this?

[LLigetfa]

I'm not Dana but will put in my two cents. You could simply cross strap it with horizontal 2"x2" leaving very small thermal bridging. My guess is you want the plywood sandwich so that you have something to screw into but you could skip the plywood and just use long screws. The amount of thermal bridging on just the screws would be minimal.

To reduce cracking at structural transitions, I avoided making butt joints on them. Instead, I floated strips of plywood between the structural members to screw the drywall to.

[dlarrivee]

I'd thought of that already, but wanted better.

[Dana]

XPS strips cut to stud width is a fairly standard solution and works well. And the dimensional tolerances of XPS are also quite good, making it pretty easy to end up with flat finish surfaces. I'd go with that.

If cost is not an issue and minimal depth is there are aerogel versions already cut to stud width for thermally breaking the studs. A 10mm thick strip of the aerogel goods is worth ~R4 (about the same as a strip of 3/4" XPS) which roughly doubles the R value of a wooden 2x4 stud. The improvement on whole-wall R is much more dramatic with metal studs than wood due to the higher thermal conductivity of the steel, but it's still significant with wood 2x4s.

[dlarrivee]

I'm impressed.

I've actually wrapped pipe with aerogel impregnated matt of some sort. The sales rep was proud because the stuff came on a roll and could be cut to fit any given pipe circumference... The rolls were nearly 300 pounds however. The 1/4" matt was said to be equal to 1" of mineral fibre that we used for the rest of the job.

I suppose my biggest concern is having a finished wall thickness that is close to a "standard", so that I wont need a custom door jamb.

Using xps, glued to the face of the stud with PL300 would work great, I suppose the plywood isn't necessary, especially if I use adhesive on both sides of the xps.