Hi, I had never heard of Air Krete before -- interesting product. They say the R per inch is 3.9, which is a touch better than dense pack cellulose at 3.7 -- probably not enough to make much difference. A well done cellulose job will dense pack the cellulose in the wall cavity such that it fills very well and never settles. It can also be done poorly and leave voids and settle, so I'd try to learn as much as you can about how good the cellulose guy is. One question I would have about the Air Krete is whether they ever have any problem with the wall drying out. It sounds like they put quite a bit of moisture in the wall. Another think to think about is vapor barriers. If you have no vapor barrier in the wall now, I would think about using a vapor barrier paint on the walls, and also sealing up all the holes (e.g. outlets). The cellulose and (I would guess) the Air Krete are permeable to water vapor, and should handle some water vapor migration out the walls, but its good to be on the safe side. Maybe you could let us know what the cellulose bid is? Years ago a friend and I were thinking of starting an insulation business. We went out on a job with a couple guys who wanted to sell their business. This was the Ureaformaldehyde foam, which has since be discredited. Anyway, these guys intentionally sprayed in the wrong mix of the the resin and catylist because the catylist was cheaper -- so they did a bad job just to save themselves a few bucks. My point is, get a good contractor :) Gary

1) If I use cap nails, won't that making the insulation less effective because of the holes? the nails have a plastic cap that will give you a decent seal and will cover the hole left by the nail. as you are nailing into a solid surface (wood) and foam coveres gaps in siding its a non issue as long as you caulk the sides to the studs. 2) energy rater, can you confirm what nerdyshopper said about leaving space between the foam and the drywall? his was a conditioned space application. in homes foamboard can't be left exposed, it has to be behind a fire rated surface like drywall. in his application they used a foil sided foamboard and I guess the radiant barrier (foil) is facing the inside of the wall, putting anything in contact with a radaint barrier is a no no as it doesn't allow the rb to reflect the heat. we put it on exterior walls withthe foil facing the brick, but not to the interior of the wall. yours is a shed.if you plan on finishing the wall out..use a dow blue board and insulate the walls with batts and install sheetrock over them..if its a fancier shed..are you planning on heating and cooling the shed? spending a lot of time in there? what is your location? there is a vapor barrier location criteria. oh and radiant barriers are for hot climates. 3) Any technique for an efficient way us cutting the foam to size so it's gonna be as airtight as possible on irregular shaped dimensions? --> The dimensions are never rectangular. Sides are like: 27" 3/8, 44" 1/4, 28" 1/8 and 43" 3/4 with odd angles. Yep, time and straight edge, and extra razors for the razor knife. cut each to fit tightly and if its too small cut a slice of foam board make it tight fit and nail in place with button cap nails seal with caulk. So you mean caulk every single place where the foam meets the studs? Is it really gonna improve the insulation? exactly. what you are trying to do is make the space comfortable enough to work in. foam sheathing will stop the air flow. if you install it with gaps you will have lots of air infiltration. this is the tradeoff...you do the install of foam sheathing material cost and time or hire a foam company for higher cost and less time. a shop is a diy imo. caulk is cheap. foamboard is easy to work with. insulation doesn't perform because of the air that moves thru it. stop the air movement and it makes a huge difference. how do you plan to finish the ceiling?

Open cell polyurethane spray on the underside of your roof will be way below the minimum recommended R Value for new wood framed homes, according to the US Department of Energy. If you have typical 2x6" rafters, you will only be getting R20 vs. the minimum recommended R30. actually 2x6 rafters are 5.5" filling the rafter bay with 6" of open cell foam meets the catherdalized insulation standard. foam covers faces of 2x's to minimize thermal bridging. see pictures linked in my previous post. Plus, unless the job includes sealing all the openings into the attic from the exterior, you will not be getting the full benefits of the insulation. (See linked document.) document linked is promoting rigid foam sheathing to exterior of roof. OP is applying foam to interior of attic at roofline. when roofline is foamed the air and thermal barrier is now at the roofline not the attic floor. leakage sites that were problematic with insulation at attic floor are no longer sucking (negative pressure) from the conditioned space below. Only if you have those leaks sealed and use closed cell foam does spraying the underside of the roof make economic sense. open cell is used in hot humid climates. not closed cell. Unless you have HVAC in your attic, you will likely be getting a much better return by insulating the attic floor as suggested above. Unless being the operative word... 90% of homes in the south have hvac in attic. and ductwork in the attic. putting equipment and ductwork under the insulation (foam on roofline) allows equipment and ducts to perform. putting foam on attic floor still puts equipment and ducts in 130 degree attic. Spraying R20 under your roof on the Georgia shores and calling that fine and dandy? I wouldn't have anything to do with either of these contractors. If you want an impartial assessment, read the linked materials or contact an energy consultant in your area. Resnet is a good source for an independent energy rater. best of luck op

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?