Insulating wall cavity with 1.5" steel studs

[Jotun]

I am remodeling my basement and have a wall where I needed a total width of 4" to match an existing stone faced wall. The rest of the basement is 2.5" EPS foam with standard studs, and .5" foam on the floor (and Advantech subfloor).

For this shallow area I was able to match the existing wall with 2.5" of EPS foam (1 inch and 1.5" layers with overlapping seams) and 1.5" steel studs against the insulation. Would it be worth putting insulation between the studs as well? I have 1.5" EPS panels I could fit inside the channel of the studs. If so, would friction fit be enough or should they be sealed somehow? I'm not really sure what's worthwhile here and the best method to use since it's a bit unconventional. Thank you.

 

[Dana]

I am remodeling my basement and have a wall where I needed a total width of 4" to match an existing stone faced wall. The rest of the basement is 2.5" EPS foam with standard studs, and .5" foam on the floor (and Advantech subfloor).

For this shallow area I was able to match the existing wall with 2.5" of EPS foam (1 inch and 1.5" layers with overlapping seams) and 1.5" steel studs against the insulation. Would it be worth putting insulation between the studs as well? I have 1.5" EPS panels I could fit inside the channel of the studs. If so, would friction fit be enough or should they be sealed somehow? I'm not really sure what's worthwhile here and the best method to use since it's a bit unconventional. Thank you.

The thermal bridging of steel studs is substantially higher than wood, so the performance of any insulation you install there will be cut roughly in half (assuming 16" on center spacing). At 1.5" EPS runs about R6, so figure on R3-R4 performance after thermal bridging. But even R3 reduces heat flow by about 25% from your existing 2.5" ~R10. If you have the material on hand that might otherwise go in the dumpser HELL yes it's "worthwhile". Gluing it to the first layer of foam with a few blobs of foam board construction adhesive is better than a friction fit, which could conceivably flex or bow out enough over time to create a convective air bypass between layers.

If you don't have enough material, carefully splitting R15 batts (rock wool or or fiberglass) into two 1.75" thick batts with and friction (and compression) fitting delivers about the same performance as 1.5" EPS, and would usually be cheaper, and (unlike low density fiberglass) is sufficiently air retardent that it won' t lose performance to convection through the batt.

If batts, seek out batts designed specifically with steel framing in mind, which are manufactured at the full 16" or 24" width, not the 15" or 23" friction-fit widths used for 2x framing.