To get responsible answers to roof insulation questions you must supply us with more information about the roof/ceiling construction, the HVAC system, and the climate.

We're in south GA, we use a heat pump and the house is solidly built with lots of wood in the attic. We installed an attic fan with the new HVAC a couple of years ago. Foam seems like the neatest solution. Or is it too good to be true?

I'm about as far from So. GA as you can get, in the mountains of CO., but we have sprayed in foam between our rafters in our upstairs (now a finished master suite). Not only is it "neat", it works extremely well for us. It is cold here every winter and the upstairs needs little (sometimes no) heat. We don't have A/C and in the summer it used to be considerably hotter upstairs than downstairs. Now the temps are closer to the same up and down stairs. It is much more comfortable now. However, we had it professionally done and it is NOT cheap. We have a 9/12 pitch roof and our house is about 50' long by 25' wide. The insulation job was around $6,000. YMMV. We didn't have any choice though because we had an expensive new roof that was not vented and when we went to finish the space as living space we could not use fiberglass bats; because of the lack of venting we had to do a cold deck. Fine with us, in the end, no ice dams at all! And as added bonuses the foam helps deaden outside noise and surprisingly really seems to kind of "glue" our creaky old house together. HTH

"Too good to be true" - have you gotten a quote yet?

In terms of sealing up a space, it is hard to beat foam. In terms of price, ouch!

Just a price comparison to the quote above - we are getting quotes for blown in cellulose for the attic right now. It is about 1000 sq ft and the quotes have been $500-$1,000. There is no way I was spending an extra $5k to cut my heating bills by $20/month for the few "winter" months we have.

bill1, are you concerned about water retention/moisture absorption with the cellulose? As you might have read on a recent thread of mine, I'm considering retrofitting the empty wall cavities with insulation and topping off insulation in the attic. Our auditor had recommended dense-pack cellulose, and many others agree, including the authors of this very informative paper about passive climate control on historical buildings (www.wag-aic.org/1999/WAG_99_baker.pdf).

But after talking things over with my father, who restores historical homes in northern maine, I'm avoiding the cellulose, as he says he spends his days tearing down walls that have rotted because of the water retained by cellulose. I have two estimates scheduled this week with local insulation companies, and the one that has the best reputation (at least as far as I can tell) has this on its website: "If Fiberglass insulation becomes wet, usually it will not lose any R-Value if it able to completely dry out. Cellulose insulation usually needs to be replaced once it becomes wet."

Anyway, just curious what your thought process is these days. Best of luck!

I live in a drastically different climate - raleigh NC. We have a pretty short season where we have to heat the house. Most of the year we either have the windows wide open (so moisture is about the same inside as outside) or we have air conditioning on (so the outside air is more humid.) We have about zero chance of moisture escaping from the house, freezing in the attic, and dripping back down.

In my case, we are redoing a redo of a 1912 colonial. The walls were all opened up, so I had lots of options. I made sure that they were sealed top and bottom against air movement and then used fiberglass rolls. That was more a matter of conveniences since we were doing 1 room at a time. It wasn't really practical to have anything blown in a dozen different times.

For the attic, there was some minimal fiberglass insulation that was either black from air movement or black and white from the bird droppings (apparently the prior owners didn't mind a flock of birds living in the attic!) I removed all of that mess then sealed everything with canned foam.

The estimate is $3420 for ~2200sf house. They will have to seal off the attic fan. Now I hear there's an odor associated with this foam. Any comments on that?

It is pointless to compare the moisture movement through a building shell in northern Maine to one in Georgia and equally pointless to compare the design of walls to roofs. If you accumulate enough irrelevant information you will not be able to find a good solution. Start with the conditions you cannot change, then the insulation you need and then design a system that addresses moisture movement rather than starting with a popular new solution and trying to find justifications for it.

Solvent-based polyurethane closed cell foams out-gas for months. Water-based polyicynene open-cell foam should be OK for habitation after a day, perhaps longer in an enclosed attic.

abbeycat, here's our real life experience. We asked our contractor about off-gassing before install and were told the material would not be toxic. Our closed cell foam had a slight smell the first day, and not even as noticable downstairs as it was upstairs. After the first day, it was not an issue at all. We did not have to leave the house and the installation contractors wore basic respiratory protection. Our relative lack of fumes could be because of the type of closed cell foam they use. Their truck said they had soy-based foam... but I did not inquire as to whether that was specifically what they used in our house. YMMV. Be sure and ask the contractor about this issue too.

Soy based foam is open-cell polyicynene and doesn't use solvents.

Correction: there are closed cell foams that contain soy but it would be misleading to say they are "soy based".

Thanks!