I know so many opinions can get confusing, but as Arkie stated Iso panels will give you much higher r value per inch. I recall Dana had also said because of the high R value than kept the interior surface of the Insulation warm enough that Moisture would not condense there. If permeability is an issue, Roofers use felt backed Iso panles that are more permeable, and probably cheaper. You don't need the sealing capability anyway if you keep with the zip panels as they are sealed at the joints.

I find it hard to believe that no insulation contractors in your area can apply wet sprayed cellulose, but if not, there is also spray applied fiberglass insulation that can be used to fill the area where the strapping is applied.

Another thought is to install your bottom and top horizontal straps out away from the 2x6 wall so that they are in line with the vertical straps. Then toe nail the vertical straps at the top and bottom to these straps. Alternatively, assemble the outer vertical straps and top and bottom horizontal straps on the floor and just stand them up like you would a conventional framed wall. The sequence would be to install your horizontal straps first, except for the top and bottom straps. Cut your top and bottom straps and lay them next to the wall to mark your vertical strap locations directly over the outside 2x6 studs. Nail the vertical strap studs to the top and bottom straps and stand up and nail the vertical straps to the horizontal straps and the bottom strap to the subfloor and the top strap to the ceiling joists.

"You don't need the sealing capability anyway "
this is incorrect. It's true that the Zip sheathing will be the air seal layer of the envelope, but since there is exterior insulation beyond that, it too has to be sealed. Air current within or behind insulation negates it's value. If you're applying two layers you can tape only the outside layer (so the inside layer can be paper faced) but with one layer it should be taped.

Posted By Bob I on 04 Mar 2013 09:11 AM
"You don't need the sealing capability anyway "
this is incorrect. It's true that the Zip sheathing will be the air seal layer of the envelope, but since there is exterior insulation beyond that, it too has to be sealed. Air current within or behind insulation negates it's value. If you're applying two layers you can tape only the outside layer (so the inside layer can be paper faced) but with one layer it should be taped.

I hadn't thought of that, makes sense.

Rob,
I went back and looked at the mutineers objection again as I haven't commented on them. A big one was bracing during construction needing to be inward only. Well apparently a single wall can be completed this way. Ok fine it's the outer wall & once all sides are up the walls must be free standing with bracing through shear panels or internal braces etc. So the outside walls are all up and brace themselves remove the temporary internal braces and begin building inner walls. As each inner wall is erected it is braced by temporary braces to the corresponding outer wall (across the top) these temporary braces are removed to install the permanent cap plate. Building the inner walls is no more trouble than building any other interior wall except for some care in layout to align the openings. Frankly it's a whole lot easier to lift a 2x4 wall than a 2x8 wall. Come to think of it I do have experience building double walls, THE STUPID WAY, out of trusses They were for a mansard roof and were 2 foot wide Where they sat on the second floor 8" at the top They included an overhang that projected 2 foot further out from the floor below at the their bottom which was a foot below the floor they sat on. I built them horizontal with sheathing AND ROOFING in sections as long as 32 feet and erected them with 2 rented wall jacks and ONE helper. NEVER AGAIN!

Seams doubling the cost of walls and labor are you now even or over the cost of alternative system Like SIPs, ICFs and SCIPs?

Hi Richard:

I did look into SIPs (R-29) and here, the walls on the main floor would cost about $4.64 per sq ft vs about $3.00 per sq ft for an insulated (R-30.8) 2x6 stick-built wall. Neither price includes interior nor outside wall finishing.

I have requested the prices for Preserved Wood foundation SIPs because my cement foundation, insulated to R-20, will cost about $11,000 (before taxes). I don't consider the 'labor savings' because that is the exact opposite of what I an trying to accomplish by building it with myself with my mutant "mutinous crew".

No one around here 'trusts' Preserved Wood foundation SIPs and my wife is really concerned about the re-sale value of a house built on a 'wood' foundation. The drainage around my house will be excellent, so I am not really concerned.

Rob.

I really like the idea of a double 2x4 wall. Could one build the outer wall. Set the trusses. Then build the inner wall with no obstructions? If one were using "advanced framing" i.e. studs at 2' centers, would the building inspector pass it?

I don't know, but a 2x4 wall with staggered studs 12" apart sounds like better than code.