Can I put rigid foam on studs to prevent thermal bridging?

Question

I'm re-insulating an interior wall & putting up drywall to replace the old plaster walls. Rather than screwing the drywall directly into the studs, I'm toying with the idea of putting a 1/2 inch of polystyrene rigid insulation along the stud, to prevent thermal bridging. I would then put up the drywall with longer screws that would go through the poly, and dig into the studs.

Is this a bad idea? Will this cause problems either during installation of the drywall or days/months/years after installation?

Answer 1

It's common to do the reverse...clad the outside in foam insulation to prevent thermal bridging from that side.

Your idea is sound. I'd suggest using full panels and then tape them. That would add additional insulation to the entire wall and also act as a Vapor barrier for you.

Another technique is instead of using insulation, install 1x2" slats horizontally across the studs every 16" and install the sheetrock to that. The theory is the same in that the only bridging would then be and the small points where the two pieces of lumber meet.

Answer 2

With air porous insulation like fiberglass (I'm assuming the 1/2 inch poly is to supplement fiberglass and not the only insulation) there are convection loops between the inside and outside.

See this paper:
http://www.ics-rm.net/dl/benefits/Principles_of_Heat_Transfer.pdf

In this regard, your poly would help reduce the delta T across the fiberglass and thus slow the engine powering the loop. I have always liked the strapping idea for fighting thermal bridging but it's not as effective against convection loops. The horizontal wood does block 1" of the loop but not the other 3.5 inches.