Welcome to the confusing and controversial world of building envelopes. To further simplify and confuse: Airtight is most important, and thermal bridging is more important than R value (to a point). Fine Homebuilding has a new Lstibureck article out on foam sheathing that is a must read for those interested in this topic. A couple takeaways: choose XPS over EPS. Strongly consider a rain screen. Upgrading to 2x6 gets you another 2" of CAVITY insulation. If youre considering foam sheathing then hopefully you know the many weaknesses of cavity insulation. I would prefer thicker foam sheathing staying with 2x4. I would also put the housewrap on the outside of the foam. Its not doing you much good between the sheathing and foam. If you get the right thickness of foam sheathing(as jlizer suggests is 1.5") then youre sheathing will generally be kept warmer than condensation temps. The real challenge of course is preventing what happens in worthy's pic. This is possible to do with tapes (ZIP system, others) and sealants but having a house wrap to integrate with flashing is a nice detail that doesnt rely on a particular chemical companies formulation. Havent done the double stud wall yet but to me it seems more trouble than its worth. It doesnt reduce thermal bridges at plates or your floor bands and eats a tremendous amount of interior floor space while reducing the amount of light (and heat for passive solar) that your windows let in. I would consider the ICFs for basement. @Robin; not everywhere else because they are expensive and dont take to changes very well. Better yet, look at pre-cast concrete walls (Superior is one brand) The complications listed above with wall thicknesses and furring for siding is one of the many reasons we have been using SIPS. Its great you are aware of the importance of air sealing. Strongly recommend you have a blower door test done at the framing stage. What you dont measure you cant improve. Here is a link that might be useful: Blower Door Test Explanation w pictures and diagrams

note that all my comments are on common practices and materials I see in my 10+ years in the efficiency business. this is not to say one product is superior over another, just itrw here in La. concerning flash & batt: I've never seen anyone do flash and batt. to get the foam company to apply such a small amount turns companies statewide off. instead they talk the homeowner into full depth..or close approximation in 2x4 walls. also note that I've never recommended foam sprayed walls, and if they go that route..foam has to completely fill the stud bay..overfill with open cell & shave flat with stud faces. never seen flash and batt on attic side of ceilings either. If you could get a company to flash & batt walls it would entail a second trip to do again a minimal cost job to do attic floor. here we don't do fiberous insulations against rooflines so flash & BIBS wouldn't be installed. I wonder why would a foam company make multiple trips to the same site where they are making mininal dollars? even if they did foam & batts or blown..it is usually different crews. so you would have multiple trips and tie up two crews. now if it was for a bulider with several projects a year..that would work. but for a homeowner with one house at most every several years..just don't see it happening. maybe in Austin Texas. I try to be that bridge that brings homeowners and trades people together. so that is my pov in all this. people in my trade are unbiased and only sell efficiency so although we don't have a material dog in the fight its the efficiency that we fight for. Davd cary & lzerarc Yes builders do use tyvek & foam sheathing. because they don't understand clearly what the end goal is. if a builder has upgraded from felt to housewrap..that to them is a big step. and now you want them to skip the housewrap?? land of mercy!! you tryin to put them out of business? LOL! here we have hurricanes. solid sheated walls with osb & cdx is the norm. putting 1" polyisocyanurate foam sheathing over the solid sheated walls and taping all the seams..tape has to adhere to CLEAN and DRY surfaces.. sealing any holes mades by trades people before then installing cladding has been our most cost effective wall to date. follow with conventional insulation on interiorr of walls and air tight drywall. you've got high performance wall. R-7 foam sheathing..R-13 to R-15 insulation..not bad for a 2x4 wall. of course air sealing also includes sealing sole plates to slabs or subfloors, proper flashing & sealing of windows and doors. Air sealing ceilings..that is a whole other post. we do walls well..but ceilings! recessed lights that aren't ICAT holes for supply boxes returns..bath vent fans..stove vents.. speakers.. and wire and plumbing penetrations. the air sealing is in the details. but it pays back in comfort, smaller tonnage hvac, better indoor air quality. another post would be fresh air requirements & how exactly do do it. here is a link to my utility co-op's energy efficiency design for new homes. while it isn't as comprehensive as I pushed for it does show lots of good information. pay special attention to the exterior wall composition. you'll see that since so many builders INSIST on housewraps that they specify that it be next to studs and sheathing over tyvek. in general: designers/architects really let us down in that they don't design with hvac & ductwraps in the conditioned space. or incorperate accurate load calcs into the house when it is in design stages. maybe some do..but I've had several architects incorperate my spec sheet word for word onto thier plans. MY spec sheets. hell, they went to college for years, IMO they should have a clue...but just my angst there! trades people should seal holes they make as they make them. hvac should be comperhensively sized..not just rule of thumb. insulators should learn where to put the foam and educate themselves in thermal boundry locations. in a perfect world. continuing education for everyone! LOL! best of luck.

Hi jgirl,Your doing it the smart way not roofing until after stucco.Out here,in order to insulate and dry wall, it has to be roofed and lathed, but cant be stucco'd until after drywall. I dont subscribe to the theory that hanging drywall will knock stucco off the walls, but that's what the county wants in the order they want it, so we gotta do it their way or the highway. We will face the chance that the stucco crew will slop on our shingles.They seem pretty professional in the way they lathed the house cleaning up after themselves and we asked them to be careful with the roof. They said that's a standard practice on all their projects to keep the shingled areas covered and they come highly refered to us, so i hope it works out. The route you are taking is the best route,imo. Scratch/brown coating is the first two coats of cementious based coats that are applied before the acrylic color coat. The scratch coat is applied rough, then the brown which is smooth and corners formed,(bullnose in our case),and somewhat smooth.Those two coats are allowed to sit for 30 days to allow for cracking, then the color coat.We are going for an old world texture.Best of luck on the rest of your build.

I'm remodeling our small bathroom and putting in a walk-in shower, where the longest side is on an exterior wall (no windows). Whomever built the house did not use plywood sheathing. The only sheathing on the house is foil faced foam board. When I redid the insulation in the bathroom, I put in ThermaFiber (mineral wool), not only for insulation but sound dampening. No vapor barrier has been installed yet. Well, a few weeks ago when it got really cold here, I noticed quite a bit of water at the bottom plate of that wall. When I checked the insulation, it was completely soaked at the bottom like sponge. Obviously, the condensation/dew point happened right where the mineral wool met the foam board. I ripped that out and have now taped the seam between the foam board and the studs, top plate, bottom plate with metal foil tape to eliminate any air gaps. What I am thinking of doing is this and I need advice on if this would work. Fill the remaining void with 3" pink foam board and seal any gaps with spray foam. Then, put a 6 mil plastic vapor barrier over that. The tile backer board is going to be 1/2" Schluter Kerdi board, so there is some more insulation. What I'm trying to do is minimize any air gaps in that space and prevent moist air from entering those stud bays. My other concern is if I got condensation in there, where would it go?