I’m planning on insulating my 11×20′ garage this season to function as a 4 season shop space. Wall constrruction is 2×4, 16″ OC with brick exterior and plaster lathe/sheetrock interior. One 20′ wall is attached to house and has fiberglass batts. The other walls are not insulated.
I was planning on adding 1.5″ rigid foam directly to the interior sheetrock then 2×4″ studs 24″ OC layed flat over top (fastened to 2×3″ nailers top and bottom) then1.5″ rigid foam beetween studs and fininshing with 1/4″ ply or extetior siding panels.
What do I do wih the wall shared with the house? I was going to add a VB to the 3 non-insulated walls, I assume I should forgoe this on the attached wall as there should already be a VB on the inside of the house.
Am I on the right track? Any suggestions?
Replies
1) Where do you live?
2) What form of heat are you planning to use?
3) What are you planning to do with the large hole in one wall known as the garage door?
4) How are you handling the ceiling?
5) If the walls are already rocked, how do you know there's no fiberglass behind them?
You shouldn't need to do anything (insulate or VB) to the common wall with the house.
Unless you're pulling the garage into the house "envelope" (to be heated with the house furnace), or you're planning to heat continuously with gas-fired, unvented space heaters (not a good idea from several standpoints), there's no need for a vapor barrier anywhere (though it won't hurt to have one on just behind the wall finish on the outside walls).
1) Souhern ontario. Cold damp winters, hot humid summers.
2) radiant heaters located high on walls.
3) Garage door was replaced last year with a 3 layer insulated roll up. I was going to supplement with that shiny flexible garage door insulation stuff and when the space on either side of the door (6") is furred out it should be fairly tight. (I realize this area is my biggest heat loss but the wife wasn't going to let me do carriage doors).
4) The ceiling is plastered with fiberglass batting in the attic space. I may have additional blown in at some point.
5) The lathe/sheetrock (don't ask me why there's a 1/2" layer of each!) is smashed to shit so I know thee's nothing behind. If the metal lathing wasn't there I'd probably rip down sheetrock and insulate beetween the studs but after tearing apart some other walls in the house it's way too labour intensive.
Why no VB? or why on the outside walls? (the exterior brick is in the process of being covered with sheathing>housewrap>pine board and batten)
The idea of insulation beetween garage and house was more for sound suppression but you're right; it might be nice to steal a little radiant heat from the house!!!
If I don't need a vapor barrier I would rather not as it's just one more thing to do for what is supposed to be a quik project that will make the temp bearable during the winter.
I'm also debating insulating the floors with sleepers and rigid foam alrhough this may make the house a tough sell should we ever move.
Basically, you don't need a vapor barrier if there's no water vapor to barricade. Unless you use unvented gas heaters or install a shower in the garage, the only source of moisture is your breathing. Not enough moisture to be a problem even if you were in the garage 24/7, even ignoring the massive air leakage that even a well-sealed garage door represents.
No point in additional insulation between house and garage since the common wall probably represents less than 20% of the exterior wall area of the house, and probably much less than 10% of the heat loss. Insulating that wall alone (and not insulating the rest of the house) will do little in terms of cutting energy consumption. And if you want sound suppression a couple more layers of drywall would be more effective than foam.