The problem with the R25 (R15 plus 10 code wall) is that the exterior insulation is expensive, complicated to install, requires specialty fasteners, and the builder needs to do some tricky things with the air sealing and the window installation. It's a pretty labor-intensive and expensive way to get R25.
So, we are thinking about an easier way to assemble the structure - using a builder to put up the house quickly and then work on all the interior layers ourselves -- indoors and out of the elements and bugs.
Rachel Wagner (Wagner Zaun Architects) presented this alternative at the 2016 Duluth Energy conference and we are thinking about a variation on this approach. It seems like a pretty simple way to get to ~R40.
So, we are thinking about an easier way to assemble the structure - using a builder to put up the house quickly and then work on all the interior layers ourselves -- indoors and out of the elements and bugs.
Rachel Wagner (Wagner Zaun Architects) presented this alternative at the 2016 Duluth Energy conference and we are thinking about a variation on this approach. It seems like a pretty simple way to get to ~R40.
Here's the layers we would use:
BUILDER TO INSTALL:
1. Vertical Siding with more that 3/8 in air gap. Eliminates rain screen complexity
2. WRB - Tar paper
3. External Plywood Sheathing - windows and deck attach to this layer.
4. 2x6 structural wall
OWNER TO INSTALL
5. Mineral wool batt insulation
6. Foam board insulation - Optional layer of any R value if we want more performance/thickness. Even 1 inch would add an extra R5.
7. Plywood air barrier - with seams taped. Continues on underside of the roof trusses.
8. Vapor Barrier - Class 2 vapor retarder paint applied over all of plywood.
9. 2x4 non-structural wall and electrical chase; filled with mineral wool batt
10. Drywall
11. Latex paint