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

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

with foam the install is crucial. inexperienced untrained installers do not get the air sealing that makes for an air tight seal. we use open cell here, full rafter depth and faces of 2x rafters covered. this is a hot humid climate. ask to see installs of jobs they have done for others or to visit sites where jobs are ongoing. insulation should not dip in and out in rafter bays but be mostly even. 6" of foam is 6".. not 3" to 6". open cell has less R-value than closed cell. and all should be installed to specific R-value spec' best of luck

"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.