Garage/Shop Heater Installs?

[gstrom99]

Good advice. I've looked (a little) at the spray foam "systems" both online and at the Green and Orange stores. They all seem kinda pricey to do a full job. I like the idea of putting a coat of an inch or two on the metal walls, then filling the rest up with batts.

 

[ovrszd]

Yes the DIY kits are expensive.

 

[PEJ5]

Get a couple of quotes from independent Insulation companies. I ended up with a professional job insulating my rim joists full (16" high x 5.5" deep) of spray foam for $100 more than the cost of the DIY canisters.

 

[gstrom99]

Looks like a good plan. The rim joist job would be hard to do with batts, and tough to make 'em stay up there too.

 

[ovrszd]

My builder says most inadvertent heat loss is at the top wall plates. When our insulator spray foamed our house walls the builder had him also foam the top of the wall plate and up the batten boards like your pics.

After he told me what to look for I started paying attention to house roofs on frosty mornings. Very common to see heat loss from the wall plates.

 

[John_Mc]

John, your building is definitely sealed tightly with no air transfer.

In regards to Spray foam (closed cell). It has an R value of 6-7 per inch. 95% of it's R value is gained in the first two inches. So in a 5.5" wall you have somewhere around R value 17. If you were after R value you would have been better served by spraying an inch to seal the building, then blowing "wet" cellulose or batt fiberglas.

Batt 6" fiberglass would have added R value 19.

The problem with Batt fiberglass is that it has too many breaks. While the batt itself is R19, you don't approach that number for the whole wall, even if you had no windows in that wall.

I agree that the first inch of spray foam has the most effect. In fact, the first inch of almost any insulation has the most effect as far as bang for your buck. (You see diminishing returns on your investment per inch for every inch after that.) The "first inch effect" of closed cell spray foam is even more pronounced, since that first inch also makes the seal.

Most of the recommendations I see for closed cell spray foam for our part of the country recommend going to at least 3" in the walls, and 4" is quite common (no one builds new construction for heated spaces with just 2x4 walls around here). Our 2x6 frames have a 5.5" cavity. It was sprayed to about 4"-4.5" thick over most of the cavity, with the part abutting the studs sprayed at or very close to the full thickness of the wall. (The studs have less R-value, and on top of that the R-value of a stud really only really works up to the thickness of the insulation. So if you have a 2x6 stud, and only insulate it up to 3" thick, you effectively have the R-value of a three inch stud for the stud itself.) We did not fill the whole cavity to 5.5" due to cost (of materials and labor: trimming closed-cell foam is a pain in the butt if it expands out beyond the cavity) and due to diminishing returns (as with any insulation). The ceiling is sprayed to at least 6" thick.

 

[ovrszd]

Another alternative that's gaining popularity here. Spray foam 1-2" then blow the wall cavity full of wet cellulose. No air transfer and excellent R value. Very easy to remove excess to stud face.

 

[PEJ5]

The standard here (Canada) is to go with R22 or R24 batts in the 2x6 stud walls AND apply 2 or 3 inches of rigid foam (R10 or R15) on the outside before installing siding. The rigid foam stops thermal bridging through the studs. The other real issue with only insulating the stud cavities is all the places where 2, 3, or 4 studs are nailed together for strength...no insulation there.
The passive solar builders are building two 2x4 walls separated by 16" and filling the huge cavity with blown insulation...R50 walls!