You can also do as AC hacker has done and use rigid foam, and just use expanding foam in a can (great stuff) around the rigid foam. You cut the foam to fit between the joists and use the expanding foam around the edges to seal it up. WAY cheaper and air seals just as well, and you get the same R value per inch if you use rigid polyiso. He has a thread somewhere about it, I think its about his kitchen remodel?

I don't think it is much cheaper, let alone WAY cheaper. Rigid foam is nearly $20 for 2x8' by 2" boards around here and there is too much waste. Then add in several small cans of foam to seal the edges... In AC's thread he said he would use my technique next time.

I didn't realize asking about spray foaming an attic would cause such division. This difference of opinion could actually be very good in coming up with a way to quickly, cheaply, AND qualitatively use spray foam.

I know how it goes, QUICK, FAST, CHEAP pick two.

We might be on to something here. Since I live in southern California, I don't really need to worry about vapor barriers as much as you folks in the frozen north.

I do have a garage that is attached to the house. I even have a contractor acquaintence who is telling me that spray foaming that bit is going to be way expensive and I should forget about it.

I like the spray foam idea in the garage portion that is attached to the living areas. It keeps out the carbon monoxide from the vehicles. I can do the same with plastic and cheaper too, however... I'm in my 40's, by myself, and have a full time job. I'm not going to leave the contents of the garage outside while I take a few days to staple plastic wrap on the ceiling and two walls of the garage. Then go tape up the staples. In this instance, spray foam would be an incredible time saver. And with the eco foam that is out there, I'm not killing the environment.

Back to my attic. Let me remind you, 40's, by myself and full time job. Would spray foam be any faster than cellulose?

And before I forget, has anyone had any experience with the foil shields you put in the attic to reflect heat?

Let me know.

Interesting. Last time I checked it out I thought I priced the rigid foam at quite a bit cheaper. I'll have to double check that I guess.

I can buy foam board up to 3" thick for $0.50 per board foot at R5 per inch of thickness, 2" thick 4'x8' is $30.50

For Cellulose a $10 bag covers 60 square feet at R19 and is R3 to 3.8 per inch, so it's cheap if you have the space and if I remember right the blower to blow it in my attic was $75 for the day, under $1,000 to make my attic R60.

Sorry to come across as negative. Recall that I did say "in an attic". In an attic you have room to spare. That's the sole reason why r60 is recommended in attics as opposed to r40 for walls. Bringing an attic to r60 with spray foam costs a LOT more than it does with cellulose. If you really want you can squirt a "flash" of foam on the entire ceiling and then blow cellulose. Or you can just air seal and use cellulose.

My 600 square foot workshop (built by a previous owner) had numerous small air leaks in the ceiling that I was not able to find and seal. So I pulled out the fiberglass, had about 4 inches foam blown in, then blew in 2 feet of fiberglass on top.

Result is the air leaks are absolutely, positively sealed and I have an R80 ceiling.

The foam cost about $1500. I got a deal from a guy that cut the price to get the order. He was starting a foam business.

Wow R 40 is recommended for walls? Is that in particular regions or everywhere? I was looking at using Tiger Foam, and an inch of that with normal R 13 fiber glass, plus what little R value Drywall and the brick outside walls have only get me to about R 20. Normal wall construction down here in Alabama is 2x4, it just about takes a fist fight to get anything thicker. Not sure how i could even get to R 40.

R 40 is the BSC general recommendation. The code here is only R 20 for walls and R 38 for attics (unless you have electric heat). If you do the energy modeling you will see positive results with added insulation up until around R 40. Above that and the windows dominate the load by such an astounding margin that it makes little financial sense to go further.

Here is a handy guide to air sealing an attic. It is very thorough.

http://www.buildingscience.com/docum...-sealing-guide

If you follow that guide one shouldn't need to put in a thin layer of foam insulation over the whole attic but just where one needs to. One could do the job oneself and seal it equally well while saving big bucks over paying someone else.