The ventilation problem is a real risk. But I believe in "build it tight and ventilate it right". This is, do the air sealing/insulation, measure tightness with a blower door, calculate air changes per hour (ACH) and install and HRV or ERV of needed.

Not dogs and cats but I've heard in some places down south like New Orleans males and females within the same immediate family tend to have sex togther. Oh wait, that doesn't have anything to do with foam in the walls,,,,,,,,,never mind. :-)

The leak problem won't show up until the roofs over the foam get old enough to leak. The big problem is that you may not be able to tell there is a leak. My opinion is that foam would be best reserved for use under metal roofing, preferably standing seam.

I wonder if you could do a variation of the cardboard inserts that preserve the air flow to the soffits, so you had an air gap between the plywood/osb on top of the joists, and the spray foam, a kind of formwork if you know what I mean.

I went to a home show today and spoke with the only people I know of in town here in BC that do sprayfoam, he says the city is yet to approve closed cell as an air/moisture barrier.

Kind of silly because I've seen very few poly barriers that are anywhere as well sealed as foam, and rim joists? Fuggeddabahdit. Mine have insulation but no plastic at all, from what I can see. Unfortunately my basement is finished with a fixed ceiling (I don't love suspended but I sure wish I had it here) so I can't really fix the rim joists, otherwise I would get them all done when I get my garage ceiling done. I don't really think the moisture barrier approval thing is an issue for me, since the house was built in the '80's (and there is no moisture/air barrier under the floor above the garage, despite it being originally a carport, and therefore a cold area)

The guy says $4.50 cdn + GST (no pst for enviro/energy-friendly stuff usually) for 3" of closed cell, I will do my sums and see if it's worth doing myself. I bet he'd be a lot faster and neater than me!

You won't have the roof issue unless you are doing a sealed attic with closed cell foam.

We have a vaulted ceiling in one area of the house where the foam is (obviously) sprayed between the joists at the roof. Our metal roof leaked there after a violent storm. We knew within 20 minutes inside where it was leaking because it was open celled foam (Sealection500).

Same thing where the overflow pan for the A/C leaked one time early on and we saw some water on the bathroom floor below. The attic is sealed on the attic floor with the same stuff. That's why we would never use closed cell foam in such areas.

We only have cats, so can't address the final question.

Thanks for the responses, that helps.

We're looking at 5" open cell on the roof and about 3" open cell in all walls before sheetrock goes back up (the advantage of a gutted house). I know the theory is that open cell allows water to penetrate and tell you there's a leak, but I've also read that it may not work as designed. Dallasbill, your story makes me less concerned.

I also went to a home show this weekend and there were about 15 foam booths. One said his method is to spread a mesh cloth over the joists and then spray foam onto that, rather than directly onto the underside of the roof. He said the air pocket that creates (1) better insulates and (2) prevents the roof from melting. I don't buy either of those arguments because (1) that air pocket would get to the same temp or hotter than the roof and (2) roofs just don't melt like that... anywhere. Any disagreements with that?

Trapped air is, in itself a good insulator. I can see the air gap thing working well if it allowed air flow to and from the soffit vents, assuming you have them, although if I envision it correctly the soffit vents would now only ventilate the cavity between the rafters and the suspended foam. You would need to add vents to provide fresh air to the roof space, assuming that the roof space is not now part of the conditioned space. Assuming it isn't, you'd need the vents.

I guess your insulation laid on top of the ceiling keeps house warm/warm air out of roof space, new foam on rafters provides further barrier to snow on roof melting, and, in summer, a barrier to heat penetrating beyond that.

I've heard of people using a perforated foil barrier, which would still allow for airflow etc.

In Australia, which is, admittedly a mostly hot climate with mild winters, it's pretty much standard to use 'sarking' which is an air/moisture impervious underlay directly under the roofing. Advantage of that is no issues of moisture damaging timber and it stops the heat right there. Most popular roofing there is terracotta or concrete tiles, followed by colorbond steel roofing.

Having said all that, I look out my window here in British Columbia and see it's lightly snowing, and it's almost April, and I wonder about the wisdom of moving back here!

I assume your attic is sealed, as that is the only reason to apply it to the roof underside.

The "mesh guy" sounds like a complete crock, and proves said with the shingle melting myth.

Yes. In fact, I think I have bigger problems than my roof leaking and rotting. I think I'm now living in a toxic time bomb. My whole house smells like chemicals, and I've since been told it's because parts A & B weren't mixed correctly. It's been just 11 days since my attic was sprayed and I feel like I'm being poisoned and I feel like I need to move out now or I'll have some really big health problems. Help.

Also, I talked to the roofer who did some excellent roof work for me, and one of his first questions was about trapped moisture affecting the rafters and shingles. Unfortunately, this was after the attic was sprayed.

2001; what state do u live in?

@joe_mn I live in North Carolina. Two or three days after I made my first comment above, I had to move out of my house. Everything in the house seems to have been saturated with the vapors from the foam, including my clothes; even my cats smell like the foam and feel sort of uncharacteristically coarse (I had to have one of my longhaired cats shaved and boarded at the vet after she began throwing up, and another of my cats developed a sort of rash on his ears and abdomen). My attic now stinks like something foul, and I noticed even after washing my clothes 3-4 times they still have a faint odor similar to the current odor in the attic (initially my clothes smelled like the foam chemical vapors that were dispersed through the house). The off gassing is so bad that if I'm in the house for just a short time I get dizzy, I feel like my brain is foggy, my eyeballs feel sticky, my sinuses become irritated, and if I stay too long I wake up the following day feeling very fatigued and like I'm coming down with a cold/flu. I also feel like there is a very fine, fine "dust" on my skin after I've been in the house; it's very strange and it seems like whatever it is I'm feeling in the air also has a very rapid drying effect as my lips, nostrils and eyes quickly feel like all the moisture is being sucked out of them. The last time I went into my attic, I felt like I was going to collapse, and it took several days to recover. Yeah, it's a BIG problem, and I'm telling everyone I meet to stay away from spray foam insulation.