1/2″ interior foam board for thermal bridging?
I’m in Long Island NY, in the northern reaches of Climate Zone 4.
I discovered termite damage in a room with two exterior walls. The moisture and termite issues have been resolved, and in repairing damage to the framing, many of the studs were sistered. With all the extra studs, I’m concerned there will be a lot of thermal bridging. To counteract this, I’m considering installing rigid foam board on the interior side of the wall framing. Immediately exterior to the wall framing is exterior gypsum (house was built in the 1960s, when exterior gypsum was apparently popular), and then there is a small gap and then brick veneer.
1. The plan is fiberglass insulation bats in the stud bays (trimmed down given the narrowed stud bays caused by the sistered studs) – I guess this should be unfaced since the foam board will function as a vapor retarder?
2. Then 1/2″ foam board attached to the framing. I’m thinking 1/2″ to minimize loss of interior room space and also because I only need to break the thermal bridge of all those studs to the drywall (and I suppose I get better air sealing as well) since I’m using fiberglass insulation in the stud bays. Is 1/2″ thickness foam board sufficient to break the thermal bridge?
3. Then drywall screwed through the foam board and into the studs. This is another reason for my leaning toward 1/2″ foam board – no need for horizontal strapping.
4. The only 1/2″ foam board available at local Home Depots is FOAMULAR 1/2 in. x 4 ft. x 8 ft. R-3 Square Edge Rigid Foam Board Insulation Sheathing. This is XPS, so while it’s not green-ideal, will it work? Also, this is faced, so I guess faced/vapor retarder side should face interior of house?
5. Is this a reasonable plan of attack? There shouldn’t be any issues drying to the outside. Would condensation on the outside face of the foam board in the summer (AC on in the house) be an issue?