2" in rim joists should really be 3". 2" of foam on ceiling..clarify please is this like on the attic floor & blown or batts to be added over foam? otherwise 2" isn't anything..big R-7 at BEST. if it is 2" on roofline...what is that supposed to achieve? it just isn't clear...to me what is being offered. keep in mind with foam companies part of the charge is built in for time to set up, mix to heat & hoses to heat up. the extra product (ie 3" vs 2") is just that ...product. doubling the amount of product doesn't double price. If foam co is being honest with you. shop around. I doubt 100 hours labor, 3 guys @ $15 each shouldn't take a week and a half to install sheathing. builder probably did quick calc of $x for foam sheathing = $xx X 2 for labor = 10k. in my area no one uses foam sheathing over 1" thick, so I don't know costs of thicker foam sheathing. but do some price checking. best of luck

Wrapping the exterior with 2" of rigid foam will prevent thermal bridging across framing members (up to 20% of the wall area!) and is well worthwhile. If you tape the rigid foam you'll also have a tight barrier against air penetration. A combination of 2" of foam on the outside of the wall and blown-in cellulose inside is a very cost-effective solution that will perform better than flash and batt. If the "flash" isn"t thick enough everywhere you can get a condensing surface inside the wall, which is bad. Cellulose is only corrosive if it's wet, and if your insulation is wet you have bigger problems than corrosion to worry about.

The 1/4" of foam or radiant barrier (actually the air in the bubbles) is meant to serve as a break for the thermal bridging across the headers and studs. Some of my walls are 1/3 solid wood that bridge directly to the outside. The aluminum foil-bubble-foil radiant barrier claims an R value of 6 with at least 0.75" of airspace on both sides for a vertical installation. I'm skeptical of this claim as well, but if installed correctly it should work in theory...I'm just not sure if it is cost effective, and I'm concerned about trapped moisture. Building Sciences recommends against radiant barriers in basements, but I haven't found much research on their use in combination with other insulation (such as closed cell spray foam) in exterior walls. I have a mixed brick veneer/wood framed bank ranch in NC (mixed-humid) and am primarily following the Building Science Charlotte Profile whenever possible, as this is a remodel not a new construction. I found the recommendation of the radiant barrier in exterior walls on manufacturer's sites, so I'm trying to gather some independent research as to whether they're truly effective.

Looking at ccspf of R7.5, plus fg batts between the studs to meet Ontario Building Code (OBC) min. of at least R24. Here's the architect's drawing for XPS on the exterior. (Instead of the polyethylene pillow on the rim joists, I will use ccspf. As well, if I use ccspf for the walls, the Blueskin can't be used as the heat of the spray destroys the adhesion, says the spray contractor.) Ratio of exterior to interior insulation. I've built several homes in our Climate Zone 5 with 1" XPS on the exterior, unfaced fg batts on the interior. I lived in one for six years and kept up with that buyer for a few years. No visible problems. Here's Dr. Joe: "I grew up with this wall in Ontario - 2x6 wall with R-5 foam sheathing (Photograph 2) coupled with unfaced fiberglass batt cavity insulation covered with an interior 6 mil poly air/vapor barrier (Photograph 3). This wall is currently being built all over Minnesota and Wisconsin. It is still being built in Ontario. And it works." * ********* spray foam under the slab I hadn't heard of that before the spf contractor made that point too. Thanks for the confirmation! I will decide when closer based on price. ********** a liquid applied air barrier in lieu of the spray foam As you say, no insulation value to that. What I typically see here on high-end infills is simply housewrap over sheathing. relocating to a more southern climate Actually, before the upper end housing market collapsed here, we were all set to move south--to New Hampshire. We're not fans of heat. Or alligators!