Please, pick one forum and ask that the other post be ignored.

"Please, pick one forum and ask that the other post be ignored."

WHY?

Not everyone reads all forums....unless they do not have a life...

Cross posting is a valuable approach to get answers from professionals who otherwise would not see the question in any one given forum.

That said, sprayed foam of any type rarely is an effective solution in any application.

Because sprayed foam can cost 5 X ore than conventional fiberglass or cellulose, and provide no more energy savings per inch, sprayed foam can take 5 X more time to simply pay for itself before saving you a single penny.

Be energy smart.

Stay away from expensive spray foams and use proven conventional insulation products like fiberglass or cellulose.

The money you save may be your own!

Thanks for the opinions. We'll get a couple of estimates and think about it.

On a new construction does not spray foam used as insulation between wall studs create an air-tight seal removing the need for a vapor barrier on the inside and tyvek on the outside?

removing the need for a vapor barrier on the inside and tyvek on the outside?

I don't believe housewrap, other than for the rims, is Code anywhere. But you do need an exterior drainage plane regardless of what interior insulation you use.

In any case, the OP is considering foam for the attic/roof. Not clear which or where or in what climate, so it's hard to give any specific guidance. There are conflicting studies on its practicality under the roof decking.

We're in south GA. Very tight attic space. Old fiberglass insulation is settled between joists. The foam seems to offer the benefit of keeping the summer's heat out of the attic, while still allowing us to remodel and not worry about cellulose falling through when we add light fixtures - LOL!

...if Mike Holmes uses it it must be good!

Well the first estimate is in: $3420 for ~2200sf. They will have to seal off our attic fan. Friends who used the same company say the foam has an odor. Any comments on that?

"Because sprayed foam can cost 5 X ore than conventional fiberglass or cellulose."

This is a gross exaggeration for what the OP has described.

The OP has not described the attic conditions very well or the foam he is asking about so I will assume it is a low slope truss system with restricted access and therefore the foam insulation proposed is probably a 1/2 lb density polyicynene free rise open cell expanding foam (60 to 1).

If so, this material is water vapor permeable, doesn't wick water, and has an R value of 4 per inch per s.f. It should cost 1.5 to 2 times the cost of fiberglass if sprayed in a wall. I don't know what the cost difference is when poured into an attic space.

If the attic is to be ventilated it might be difficult to install eave vents that are not blocked by the foam. It is likely the attic would be sealed.

We added foam insulation in our crawl spaces upstairs and around the foundation gaps in our unfinished basement after having an energy audit. It seems to work well, doesn't crumble into the area when bumped, and it definitely takes up less space than the old batting. You are right about the smell...it was pretty nasty for a couple of days, although I'm fairly sensitive to that type of thing and my DH wasn't as bothered by it as I was. I recommend doing it in a season when you can open windows.