I've got the answer for you... If you're planning on finishing the interior walls and you want the house to be real tight, you should consider using icynene foam. Icynene does have to be installed by a contractor, but I recently insulated a 3000 sf 1850s post and beam farm house with it and the entire intstallation took about 2 hours and was less expensive than estimates with traditional fiberglass bats. The materials are more expensive, but the labor was cheap! Icynene will give you a complete seal - NO drafts and no need for roof venting. It does not have as high an r-value as other poly based foams, but it is water based and does not off-gas so it is very GREEN. It still has a much higher r-value than rigid foam, or fiberglass, and by virtue of creating a complete seal, will HUGELY increase the efficiency of your home. You are lucky in that your interior walls are not yet finished. Sprayed on foam options aren't great if you have to strip the interior walls first. Icynene is the ONLY option I'd consider in your situation. Good luck.

I would go with the 1.5" insul board and forget the strapping. It is more important to have a continuos run of insulation than the extra thickness and with the strapping every 24", there is NO insul board covering the wood at that point. Just mho.

I definitely want to keep things simple. I was aware of the zipR shearing but I have heard it is typically cheaper to use regular zip board and a separate rigid foam. I don't like house wrap because I think 90% of the residential house wrap is not installed per manufacturers recommendations. I work commercial construction and have seen the tyvek required installation methods and rarely see that in the residential market here. I also thought I could save money and give me the piece of mind by taping the seams myself. I will look into the price difference on the zip sheathing and separate foam and the R-zip. Might be the way to go if it is minimal difference.

Here's a bit more info to give you a better idea. Zone 5B, Cold winters, hot summers (rarely humid but like this year...humid and hot summer!) My walls will be 2x6 with either dense fiberglass or mineral wool insulation (products readily available locally). My current debate among my thoughts is trying to decide about the WRB (MY HOUSEWRAP) and at what tier/level/plane to install it (Or even two). Windows are not permanent, and in a forever home (God willing), windows will need to be replaced in the same lifetime I live. Therefor, I don't want to choose some method that would hinder future upgrades/replacement. (Such as installing foam over a flange so it must be cut out, or installing a type of flashing that requires more of the foam wall or window box to be torn out to replace the next time around. I am debating between a quality house wrap to prevent moisture and also act as an *air* barrier not a *vapor* barrier. Basically, on a cool winter day with 50 MPH Wind, I don't want that wind (air) easily permeating through the house because I will a.) not be sealing the joints of foam b.) possibly not even taping the foam joints c.)not going to use any internal poly as a air or vapor barrier. I am not sealing the foam joints because foam shrinks and expands and those joints will not stay tight forever. If I have the luxury, I will install (2) layers of 1" thick versus (1) layer of 2" thick to provide staggered joints and prevent air from moving inwards that much more. There is a wealth of information on greenbuildingadvisor, but it seems to boil down to personal preference on two things. One being that I can opt for innie (windows set towards the OSB wall sheathing layer) or outie (windows that are at the most exterior plane as possible). And we all know that flashing a window opening is important for multiple reasons, and that the standard way includes integrating your house wrap (WRB) into the rough opening with multiple methods. I would like to use a flexible peel & stick flashing that will seal to/against the house wrap. My concerns for those who have rigid foam on the exterior are a.)where did you locate a house wrap (Or WRB)? and b.)in what fashion did you set your windows? It varies by foam thickness, but generally 1.5"+ of foam requires framing out a window frame/buck for window support whereas under 1.5" doesn't seem to need the additional support. And of course the other option is the fasten the window like standard construction, on the sheathing level right against the sheathing (osb in my situation) and into the studs. This would then mean I would either use the WRB at the same time to detail the window opening, or perhaps not. But also means I would have to design a custom flashing to cover the exposed foam around the window, since the window is set inside from the foam and siding. I am surprised house wrap (a WRB) seems to not be the norm. It is here...and it is something I do not want to overlook. My understanding is that in new construction with rigid on the outside, builders extend the window opening (like you said Mushcreek) to the same thickness as the foam, therefore that foam will not have an exposed edge. I read on GBA that instead people build plywood boxes for the windows the thickness of the foam + 3/4" and then use a 1x3 or 1x4 flat around the window opening fastened thru the foam into the window opening studs. Then the window flange is fastened to this flat 1x3 or 1x4 frame, and it also brings the window out the extra 3/4" so that 3/4" firing strips can be used to install siding. I do not think house wrap *over* the extended window frame would be as effective as if I just installed the windows flush with the foam level, allowing my flexible sticky flashing tape to easily fold over the opening and adhere to the foam. ---starting to think I should just not be so concerned about this detail. Turning my hair grey.