Spray foam insulation inside existing walls

[Bill Dufour]

Wondering about spray foam insulation for the next home. Everything I read about spray foam says spray it in layers not more then 2" thick after it foams up. If it is sprayed to make 3.5 inches or more in one shot it will not cure correctly, may shrink later, may never stop smelling etc.
But then they say go ahead and fill up a 2x4 or 2x6 wall cavity by drilling a small hole and shooting it full in one shot. I know the retrofit stuff is slow expanding maybe not self supporting in a overhead shot so it is not used in exposed bays. Probably costs more as well.
So Is it okay to spray foam a full stud bay in one shot? there is no way to do two shots. I assume they use extra long nozzles to get to the end of things like in dense pack insulation. I bet in dense pack they charge extra and ditch the long nozzle when no one is looking to save on time and material. No one can tell later anyway.
It does surprise me that PC correct California still allows r13 in walls instead of r15. That would seem like an easy non-controversial upgrade.
Bill D

[Edward Dyas]

I've seen it done but don't have experience with it myself. The guy would spray one coat between the studs and it would swell up and slightly out from the studs. Once dry they took a blade and shaved the excess off. As far as the smell I saw it a few days later and didn't smell anything but I've been around chemicals so long I can't smell it anymore.

The only bad thing I can say about the foam in general is the stuff like Great Stuff. I've had a lot of trouble with ants getting into it chewing it up and removing it.

What I would check into is the flammability of the foam. I would think if a house caught on fire it would be almost impossible to put it out.

[Jim Becker]

I would imagine, as you mention, that the product being use for hollow existing walls is going to be very different than the closed cell foam I have in the 2400 sq ft home addition I added in 2008. I don't recall them spraying in layers, per se, but in the 6" wall portions as well as the roof rafters, there was more than one pass for practical reasons at least. I honestly was unaware that anyone was spraying foam into wall cavities like that...

[roger wiegand]

There have been a lot of problems with spray foam in closed cavities, I don't think it is done anymore around here. Problems range from voids to incomplete cure to overexpansion bowing or breaking the wall material. Doing it correctly requires a very skilled operator.

Dense pack blown-in cellulose is the universal recommendation for retrofit insulation in New England these days. We did that combined with 2" of rigid foam and air sealing over the entire exterior to give us a vert tight, highly efficient house. We did spray foam in the attic and rim joists, as they were accessible.