Thank you Rollie..love the way you break it down. It is amazing the difference it made years ago when sheet products became available. Prior to that walls/ceilings were made of individual boards..then all of a sudden 32 sq ft with no holes in them. Great for reducing air infiltration. With sheetrock you are sealing all the gaps where the rock joins and if you seal the penetrations you make a lot of air tightness can be achieved.Always seal wall to ceiling joints even if installing ceiling moldings. The detail work..sealing sole plates,around electrical outlets, dryer venting through walls..caulk is a great thing! In unvented attucs choosing ICAT recessed cans and not IC cans, sealing all gaps around bath fans.. stove vents ..fireplace vents this makes an excellent air barrier. Once the air barrier is complete then any insulation will perform better. what lowers R-value is air movement and misinstalls. I would recommend that you also insulate the bonus room area. In my climate these are problem rooms as they are surrounded by hot attic air..as opposed to exterior walls which are exposed to outdoor temps. Attics reach 140 degrees here. If you eliminate the foam in this area you will pay for not installing it in comfort and utility costs. It just doesn't make sense to me to not use the better method for the area where living space is in the attic... air seal then insulate walls conventionally roofline with foam. over bonus room also. savings from wall foam will pay for bonus room install best of luck,

to focus back on my original questions... I can't do ICF, that's not an option. The type of construction is fixed and the builder is not a custom builder. I have to keep the options and suggestions down to something that can be accomplished without any changes to the basic design considerations, hence windows, insulation and limited sound abatement. The house would be in northern va, so a mixed climate. I don't have a choice on MI Windows, so I have to do the best with what is available. My research so far shows they have a few different lines, the "best" line appears to be their EC line, vinyl extrusion with a honeycomb structure in some of the sections. Anyone have actual experience with that line? They have a bunch of "best product" awards, which mean nothing. I see lots of negative posts here from the same people over and over, and they may be super knowledgable but I still see no information that DIRECTLY shows me something I can bring to the dealer about these windows. The insulated sheathing vs non insulated (zip vs zip-r in my case) does this require any major changes in construction? Other than taking into account the extra inch and a half used? Anything else I should think about? The airtight construction technique looks to be using caulk around drywall and floors. I'm going to see what they think about that as well as spray foaming the areas between floors and caulking/foaming all penetrations etc. Should I insulate under the slab? I'm guessing no, but I just don't know. Basement is not a walkout, but it will be finished.

Hi I’m just jumping on here to get some clarity for myself.... we do not need a new roof right now. We want to expose our ceilings rafters in our 1920s home. It’s a two story with radiator heat and we’re in Colorado so we need insulation. From what I’ve read the insulation needs to go on the outside of the roof boards which sounds like we would need to take the roof off to do this. Is that the case? Exposing the ceiling would mean redoing the roof at the same time so we can add insulation and then put the roof on top of that?

"I was thinking the one big advantage of 2x6 here is that the framing portion goes from R3 to R5 - a rather significant increase. I would also guess that 2x4 construction would be laughed out of Minnesota." Yes, but also remember that a stud transmits heat about twice as well as stationary air so every stud that is connected to both the inside (sheetrock) and outside (sheathing) acts as a thermal bridge that sucks heat out of the house. If a cavity is fully insulated then a 2x6 stud will transmit less heat out than a 2x4 stud will but it will still suck heat out. However, if the cavities are not full then the exposed sides of those studs become cold sinks. They suck heat out of the air space between the sheetrock and foam insulation. Heat in the room goes through the sheetrock in to the air cavity and then in to the side of the stud and out of the house. In effect bypassing the foam insulation. When calculating whole wall r-value (by first calculating whole wall u-value) most houses use a 'framing factor' of 25%. These bits of the wall have a higher u-factor because they transmit heat out much better than the insulated portions. However, with bits of stud sticking out acting as cold sinks the framing factor will be higher. Rather than a 2" width of exposed stud we now have about 6" of exposed stud (2" on each side plus 2" on the face). So all of these studs will create a much higher framing factor and so much higher u-value and much lower whole wall r-value. So, doing a very quick calc on one of our walls... I came up with an actual framing factor of 32% using the traditional face method. When adding in the exposed sides of studs if we only did 3" of closed cell I get a framing factor of 63% (many of the studs that calculate in to the framing factor, such as jacks, are sandwiched between other studs so do not have the exposed side). So while the r-value for the cavities is r-21, the whole wall r-value for a 32% framing factor is r-11 and the whole wall r-value including the exposed sides of the studs is r-6. R-6 is quite bad if that is indeed what it is. So in this case, if there will only be 3" of insulation in the cavity, a 2x4 wall will actually be more energy efficient.