This weekend, we reached the final exterior layer of the building envelope: the siding! (In this case, “exterior” is considered as anything outboard of the framing.) We started the day by installing two perpendicular layers (1×3 & 1 x4) wood strapping over the continuous insulation and second layer of house wrap. The first layer was run vertically, spaced 16″ on center to align with the wall framing. We attached it by driving long screws through the strapping, outboard insulation, and sheathing and into the studs. Since our siding runs vertically, a layer of horizontal strapping was also needed. This was installed similarly to the first layer, but using even longer (7″) screws and countersinking the screw heads to create a flat surface for siding application. These two layers of strapping provide a solid attachment point to nail our siding to. The strapping creates an air gap between the siding and house wrap, so any water that manages to get behind the siding can drain freely downward; this air gap also encourages air circulation behind the siding, promoting further drying of any moisture in the assembly. This 3/4″ air space does unfortunately offer an inviting space for insects to congregate, and must be detailed to prevent curious critters from getting in. To this end, we placed a strip of Cor-A-Vent at the bottom of each bay between vertical strapping courses. Cor-A-Vent is a corrugated plastic product with one end wrapped in a screening filter fabric; it allows air to pass through, but not insects. With both layers of strapping installed, we were able to finish our day by putting up the first piece of vertical siding. Exciting!
So far the majority of our time has been focused on the various layers of the building envelope. The building envelope is what separates “inside” from “outside”. Good design and detailing of the building envelope is the most important passive design measure when it comes to minimizing building energy use and ensuring thermal comfort for building occupants. The Hygge House’s building envelope, when finished, will be made up of 9 separate layers: Drywall, Intello air/vapor control membrane, 2×6 wood framing (with dense pack cellulose insulation in the cavities), plywood sheathing, Mento house wrap, Gutex Multitherm wood fiber board insulation, another layer of house wrap, wood strapping, and finally vertical tongue & groove rough sawn wood siding! Each layer performs one or more of the essential building envelope functions: providing structural support, protecting components vulnerable to moisture from bulk water, providing an air and/or vapor barrier … and presenting an attractive finished surface to people inside and outside the building!
This was the last weekend that the courses was officially in session. Since many members of the class are graduating and some have plans to leave the area this summer for jobs or travel, a celebration was in order for the last weekend we would all be at the build together. Kent and his wife, Lynn, generously provided us with lunch, and we all got to enjoy some great food on our lunch break while reflecting on our experiences of the build. Those of us who will be staying in the area over the summer will continue to work on the house on weekends until it’s ready to load onto a truck and travel to the Green River Festival. We’re no longer being graded on participation, but watching the project come together provides a strong incentive to keep showing up!