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I am renovating a room with 2 x 4 stud walls. I’ve removed all old plaster and insulated the exterior walls with fiberglas. I’d like to add r-value without additional framing and significant reduction of room dimension. Location here is mid-Atlantic.
I was thinking of adding 1/2 inch foil-covered rigid insulation on the interior over the studs, attaching new drywall with 2 inch drywall screws. This would reduce heat flow through the framing (lots of studs in these walls) to the interior.
Does anyone have experience with this? Any problems with stability or flatness of the drywall and seams when screwed to the studs through the rigid insulation?
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It works well, I've been doing some of this for years now. I've even used foam and 3/8 rock on outside walls, (so old trim would go back on just right. No problems with rock joints or nailpops if you do careful work.
*As lonecat said, it's not a big deal. I have done it many times. A couple hints: if you use roofers to put up the foam, make sure you sink them all the way, and use the least amount possible. Double screw all the drywall (use two screws an inch or two apart) to make sure it gets sucked all the way in. You will need jumbo (1-3/8") corner bead to get nails into the framing on corners. And when you are done a stud finder will no longer work because of the foil on the insulation. Good luck.
*Thanks, Nick, for your helpful advice! I appreciate it.
*Maybe too late for this idea now that the FG is in place, but another approach that would give good R value and also greatly decrease air leakage would be to spray 3-1/2 inches of urethane foam in the bays. You'd get R-24 plus seal up all the air leaks without reducing the room size at all. More expensive that FG batting, but probably cheaper than furring all the studs out to give enough room for more FG batting. I'd pay $1.85 per square foot for 3.5", R-24 of urethane, installed, but then I'm in the sticks. -David
*Do be careful -- when I did this for the first (and only) time, the screws did suck the drywall into my 1" rigid insulation a bit. Only saw it after I put the primer on, had to fix it with more joint compound. Also check your fire codes -- in my area, I put 1/4" drywall over the foam, only to discover later that 1/2" is specified over foam. Had to add another layer.
*Consider using r-foil insulation it is only 5/16" thick, has an r-value of 8.3 up, 14.3 down, 9.8 horizontally. It comes in three widths 16", 48",72", it costs less than 2" extruded polystyrene, and is a vapor barrier. It is a real time saver and it is tough as nails. Check it out at http://www.tvmi.com
*The 1/2" foam board (polyiso) I bought doesn't seem very rigid. The first batch of 1" I bought was very rigid, but the second batch was much more brittle, though the same brand name (and rating). Check around, and test whatever you decide on before doing the whole house.
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I am renovating a room with 2 x 4 stud walls. I've removed all old plaster and insulated the exterior walls with fiberglas. I'd like to add r-value without additional framing and significant reduction of room dimension. Location here is mid-Atlantic.
I was thinking of adding 1/2 inch foil-covered rigid insulation on the interior over the studs, attaching new drywall with 2 inch drywall screws. This would reduce heat flow through the framing (lots of studs in these walls) to the interior.
Does anyone have experience with this? Any problems with stability or flatness of the drywall and seams when screwed to the studs through the rigid insulation?