Sharp-eyed observers may have noticed that the roof of the second floor is asymmetric. In the spirit of "form follows function", the south facing roof plane is larger than the north facing roof plane in order to fit more solar panels than would have been possible otherwise. Will it look a bit odd? Yes. But hopefully only a bit.
Another thing that you may have noticed is that the house appears to have no eaves. In the more traditional method of framing a house, the roof rafters would extend beyond the plane of the walls to create the eaves. But that would create a "thermal bridge" between the interior of the house and the exterior. A thermal bridge is a path for heat to travel without encountering any insulation.
In this house, once the windows are installed, the entire house will be wrapped in 4 inches of rigid foam insulation and the eaves will be added after the foam in order to minimize the thermal bridging. I say minimize rather than eliminate because there are a few penetrations that seem impossible to design away (I'm looking at you, plumbing vent stacks.)
Ultimately it should all wind up looking like this:
|Front elevation by Steve Baczek|
Because there will be so much insulation on the outside of the walls, there's less need for insulation in the stud cavities. I will still be getting dense-pack cellulose blown into the stud bays but having so much insulation on the outside allowed me to specify 2x4 walls rather than 2x6. This will give me around R-22 on the outside and about R-12 on the inside, as well as about 30 additional square feet of interior space.
At some point, I'll write a more detailed post about the wall and roof assemblies.
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