Batt insulation vs spray foam?

[kj_mustang]

I also dont know how you replace a damaged metal panel when sprayed in place.

If it is closed cell spray foam, I know you can just pull the metal away from the foam. I did it on my building. I had a dent in a ridge near the bottom of a panel caused by a mower, so I removed some fasteners and pulled the panel back and fixed the dent. Quite easy.

 

[haugy]

If foam too thin the inner surface could become cold enough to condense moisture (thinking foam and batt now = someone trying to cheap out). Rule is simple: vapour barrier must be INSIDE of the location of the freeze zone ( the point along the temperature gradient from inside to outside where it hits zero C = 32 F).

While I won't overly debate your statements, because they are mostly accurate, you're speaking for Northern areas only. What applies to you doesn't always apply to others. For example, our vapor barrier goes on the outside because we're a warmer climate. Vapor barrier should go to the side that is warmer and incurs more moisture. In the north, that would be inside of the insulation. In the south, that's outside of the insulation against the metal.

And to add, going with Foam and Batts is not the cheap way out. In fact, foam + batts has a higher R-Value than foam alone. If the closed cell foam is properly applied, it creates the air/water barrier as you've noted. But then the air between the foam and batts allows the batts to truly do their work, and you get a higher R-value. I had 1" closed cell in my 6" thick walls. Then came in with R-19 batts. My 30x40x14 was kept cool in the summer by a single window unit AC, and above 50° in the winter from one safety heater, and an occasional hanging shop heater to heat it up in a hurry.

By spending for more foam, it would have cost more, and only gained me about another R-5, for a total of R-10 in the walls. My way I got an R-20+ easily.

 

[cannuck]

While I won't overly debate your statements, because they are mostly accurate, you're speaking for Northern areas only. What applies to you doesn't always apply to others. For example, our vapor barrier goes on the outside because we're a warmer climate. Vapor barrier should go to the side that is warmer and incurs more moisture. In the north, that would be inside of the insulation. In the south, that's outside of the insulation against the metal.

And to add, going with Foam and Batts is not the cheap way out. In fact, foam + batts has a higher R-Value than foam alone. If the closed cell foam is properly applied, it creates the air/water barrier as you've noted. But then the air between the foam and batts allows the batts to truly do their work, and you get a higher R-value. I had 1" closed cell in my 6" thick walls. Then came in with R-19 batts. My 30x40x14 was kept cool in the summer by a single window unit AC, and above 50° in the winter from one safety heater, and an occasional hanging shop heater to heat it up in a hurry.

By spending for more foam, it would have cost more, and only gained me about another R-5, for a total of R-10 in the walls. My way I got an R-20+ easily.

Not living anywhere near warm areas, I never even THINK in those terms, so thanks for setting that part straight.

R20 is not the goal in the North, R40 walls are. It takes over 4" of perfect (i.e. not likely to happen...except from board or MIPs from a reputable factory) or more like 5 1/2" of field sprayed decent foam. THAT is what I mean by cheaping out as your combination of 1" foam (may or may not make good vapour barrier at that thickness - HIGHLY dependent on skill of the applicator and material) and is at best R5, but compressing the "R20" fiberglass does NOT maintain the same insulation quality and would cost significantly more than your foam + batts. You are probably right that you DO have a safe and realistic R20 but you can't just add the 5 and 20 and get 25 when compressing the glass batt.