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?

There were "concerns" about the insect-proofing used on cellulose. Nothing actually proven, but the OMGTOXINS!! crowd started a big uproar about all the possible chemicals and potential carcinogens on the recycled newsprint (it's 50%+ post-consumer content) and many retailers decided to stop carrying it. Fiberglass requires no fireproofing and has no printing ink. Before you start blowing insulation: Are you planning any ductwork, wiring and can lights? If so, postpone the insulation until they are done and inspected. The insulation blower and raker should be the last person in the attic. Make sure you have the baffles (the nail to the rafters) so you can pile insulation along the outside walls without blocking air flow up through the soffit vents. (if you have them) Blowing fiberglass (it's in small chunks) is a PITA, but with a painter's disposable paper overall, a hood and a mask it's not hazardous. Do it in early morning, and shimmy out of the overall so it turns inside out with the fiberglass on the inside. Then take a shower and wash your hair.

It seems to me that you should answer two questions. Do you want conditioned space in your attic? How much money are you willing to spend? Our story: In our 1/2 story remodel we have conditioned living space. It had always been living space (at least for 70 or more years of our home's 97 years). During the depression there had been vermiculite in the space above the ceiling. In the 1950's parts of it got fiberglass bats in the space above the ceiling. (It had always been finished like an after thought, pressboard walls, and even cardboard over 1xs during the depression!) When we gutted the poorly finished space, we decided to have cathedral or loft type ceilings. Our roof does not have any vented soffits, nor a ridge vent either, so we had to have spray foam insulation in order to do the cathedral ceilings and have some kind of insulation. It did cost a small fortune (in our estimation), but it is highly effective. Between that and foam backed roof sheathing we have a cold deck roof. Unless the snow load is wet/heavy, we don't have to shovel it; the entire roof melts evenly with virtually zero icicles and no ice dams. The 1/2 story space needs very little heat, there is more sound proofing to the outside than before, and this will sound odd, but the foam literally glues your house together. Kind of hard to describe. Our space has been inspected by structural engineers, don't worry! But before the foam was sprayed you'd arrive at the top of the stairs and walking in certain spots created "creaking". After the foam was installed, no more creaking. We are very satisfied with spray foam. YMMV Others who will post here clearly prefer blown in cellulose. Since I have no experience with that type of insulation, I hope they will post about it. Hope you get the information you need and end up with a space that meets your needs.

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?