I am in the early stages of building a 5000sq ft house in the mountains east of Salt Lake City, Ut. Temperatures will range from -10 to 90. I would like to do a double wall of 2X4s with a 5" gap making it a 12" wall. The r-rate would be 50+ and ceiling 60+. I would spray 2" closed cell against the outside wall and 10" of cellulose to the sheetrock. My architect thinks I'm nuts and thinks I should do 2X6 single wall with zip/1"foam sheathing with 2" foam and 3.5 inches of cellulose inside. A study by Building Science in Oregon stated that its not a good idea to put foam against the outside wall because it would increase the moisture content on the sheathing. The humidity level is much lower here generally and I'm not sure the zip board being treated would make a difference since you don't tape the inside edges. I plan on using Hydronic in floor heating on both levels. Basement will be in the ground 48". This brings up another question for the basement slab. Is it reasonable to do the 4" slab then do 2" ESP foam, then the pex with 1 1/2 concrete. I have watched the concrete folks consistently not pull up the pex and wire to the mid point. All floors will be tile. I will most likely do my own install. and framing. I have just finished Siegenthaler's book plus 12 hours of your comments of you forum. So my head is terminal, be gentle.

In that environment an open diffusion wall works well, if you are going the double stud wrought. Look up Thorsten Chlupp, Reina Properties He builds Passive House buildings in Fairbants. You can build a net zero in the Utah mountains that is economical. I've done it with an ICF building in Park City. 10,000 square feet, off grid, self heated, self cooled, self electrified, no utilities. What are you trying to do? What are your goals.

It also sounds like your Architect is questionable for your wishes. It is easy to design a home that heats and cools its self passively in SLC. Lots of Sun, High exposure. Yu need High internal mass, super insulation, good windows, doors, sealed completely, HRV, Solar thermal, Thermal storage tank and throughout the standard HVAC systems. No utilities for heating and cooling will save you $400 a month on a 5000 sf house. That is 10 to 20 K savings in HVAC $400 a month saving in utility costs is $100,000 of mortgage. Making the house Passive will cost less than $120,000 additionally meaning that it is a net positive cash flow from day one. https://www.facebook.com/ICFSolutions?ref=hl to see house built in Park City Utah

Brian

In that environment an open diffusion wall works well, if you are going the double stud wrought. Look up Thorsten Chlupp, Reina Properties He builds Passive House buildings in Fairbants. You can build a net zero in the Utah mountains that is economical. I've done it with an ICF building in Park City. 10,000 square feet, off grid, self heated, self cooled, self electrified, no utilities. What are you trying to do? What are your goals.

It also sounds like your Architect is questionable for your wishes. It is easy to design a home that heats and cools its self passively in SLC. Lots of Sun, High exposure. Yu need High internal mass, super insulation, good windows, doors, sealed completely, HRV, Solar thermal, Thermal storage tank and throughout the standard HVAC systems. No utilities for heating and cooling will save you $400 a month on a 5000 sf house. That is 10 to 20 K savings in HVAC $400 a month saving in utility costs is $100,000 of mortgage. Making the house Passive will cost less than $120,000 additionally meaning that it is a net positive cash flow from day one.

Brian

have you considered SIP's panels, you can have walls & roof done in about 2 days...............