Spray foam in attic

[David]

Anyone in a hot climate used spray foam in the attic? I've heard great things about them in cooling and mixed climates. I have heard of few people who've actually done it in a hot one.

I don't see how foam insulation in the rafters will help keep the heat out. The sun bakes the roof for so long, it'll eventually cook the attic. But since it's closed off, an exchanger needs to replace the air. So does it replace it with cool air from the a/c unit? And if so, a huge attick would require a lot of tonnage from the a/c. Which leads me to believe I'd actually have higher (or much higher) electric bills. Keep in mind, our electric bills are huge down here already. Adding more to the bill is adding more to the highest rate (as we're charged in tiers for usage). Doesn't sound attractive to me.

Any thoughts on this one?

[CThomp]

How about just vented soffit and solar electric roof vents to actually suck the air out?

Some of my neighbors have them and they seem to work fine.

Is your roof hipped or gabled?

A buddy of mine has a 2400 sq/ft house on stilts with soy-based spray foam insulation throughout. I think he said his last power bill was $85 or so.

[David]

I'm preparing for a new house - still trying to design it. It's about 3000 to 3500 sf foundation. The right half of the house will eventually/hopefully be finished in the future. So the roof is pretty complex, IMHO. Hipped - for sure. Gabled - possibly. Such a complex roof would require a lot of spray foam.

[CThomp]

That friend of mine had his whole house done for $11K. And that was for the entire house. The attic, the floor system, and the walls. The house is totally sealed with this stuff. It's freakin quiet to. You can't here a sound in this house.

Here's the house:

http://www.leepa.org/dotnet/Photo/Photo.aspx?Id=455232&Width=640

[Roy J.]

I worked on a house a few months back with foam spray in the attic and walls--it seems like it's a great way to keep the bugs and vermin out of the walls though I'd dread ever having to cut into the roof for an addition. The ceiling was toungue and groove with no insulation. I wondered about how the cool air would transfer up into the attic requiring the a/c units to essentially cool all the attic space too.