I used 2" and cut the pieces out of a 4x8 sheet and cut them 1/4" or so shy of the average bay sizes to give room for the foam to go in. I had a few that didn't want to stay against the rim joist as they were foamed and I didn't have any washer nails to hold them in tight. The few that gave me trouble got marked with a marker and I drilled a few holes in the foam board and shot foam in the back side and let it sneak back out the holes and shaved the excess off. it is a night and day difference between the foam board and just having batting stuffed up in the spots. I don't have a heated basement and can tell a world of difference. I think I got around 30 plugs out of one 2" 4x8 sheet of foam board with a few pieces left over for odd sized spots. One can of great stuff foam did between 8-10 plugs with a price around 6 bucks a can and the sheet price of $22.50. Once you get set up and going it doesn't take too awful long to do. I got the ones with obstructions fitted with a hand saw and in place first and then stuck 10-12 in a row so I just had to concentrate on foaming. I noticed that if you spend too much time putting the foam blocks in after the can has been partially used it wouldn't go near as far as if you started foaming and went from one to the next.

You don't necessarily need the degree days. Just go to the REScheck site linked below and enter the project information to see if the design complies with the energy code for its location. All residential projects I have designed in the last 10 years have been required to have a passing REScheck score. All but 6 states currently allow it's use as evidence of energy code compliance. It's major advantage is that it considers overall energy use (insulation thickness and mech. equip. effeciency) and allows you to shift insulation and equip. values to see what combination is most effective. You can also download the software at: http://www.energycodes.gov/rescheck/download.stm Here is a link that might be useful: REScheck online calculator

"madpebs87 "plus then you might actually have to seal some of the holes in the ceilings." Wouldn't you do this anyway? You foam the roof deck/rafters, do nothing to the ceiling for insulation, why would you not seal all the plumbing/lighting etc holes that go up into attic? Great thread (bookmarked) giving me lots of info when i build in 3 years in coastal ga." been out of town so just getting to answer this. when the attic is vented, you absolutely want to seal all openings between living & attic space. when the attic is unvented & foam sealed, then you want air exchange between living & attic space. you can get this exchange from not sealing the openings that trades make & never seal, or seal it up tight and dedicate an exchange air pathway. problem is...seldom does anyone seal these openings, so adding a dedicated pathway is redundant. people think they built tighter than they actually did in my experience. but it is all just a guess until you blower door test to see what leakage actually exists. build tight, ventilate right, and TEST to find out what performance actually is. OP, I have to defer to folks in climates with basements, as we have too high of a water table in La. for basements. I have no hands on experience with basements, best of luck.

I'm glad to come across this thread because I'm also trying to figure out whether/how to add blown-in insulation to our attic, and possibly radiant foil. I hope I'm not derailing the thread by tacking on. Our home is a roughly 120 year old Victorian, and it also has a sprinkling of old insulation in the (sealed) attic, but nothing more. And when I say attic, I should clarify--we actually have a finished attic/third floor but the very peak of the attic, above the ceiling of the finished area, is unfinished. It's like a capital A, where the lower half is the finished portion and the upper half is unfinished. I'm sure there's proper terminology for that but I don't know what it's correctly called. We use the finished portion regularly, or at least we would if it didn't get very hot up there in both the winter and the summer. In the winter, we can counteract this by closing the HVAC vents so the attic is only heated by the hot air rising through the house, and that works well enough. But in the summer, we add two window units in addition to the house AC (to cool a space that's probably 400 sqft)--the window units are kind of a mixed bag because with the way they're installed, they let in a good portion of hot outside air around them through the window. We're contemplating replacing the window units with a minisplit system in the attic alone, but I feel like it's worth exploring all the various possible ideas to try to keep summer heat out of the finished portion of the attic before installing a whole new additional system. Any thoughts or ideas for me?