Efficient, Strong Framing
A powerful emphasis on advanced framing techniques for a passive house.
We used advanced framing wherever we could throughout the California FHB House. The 24-in.-on-center spacing with stacked framing members from the rafters to the foundation provides a continuous vertical load path, reducing stress on individual framing members in the structure. Reducing the number of framing members means slightly reduced labor costs, and it increases the space for insulation, which will save us money in the long run.
Our framing plan also had to consider the effects of earthquake tremors on the house. While we’re not in the Bay area, we have to build to the same seismic requirements. To resist these forces, we need to tie the building together so the structure acts as one unit. Our engineer, Mark Jokerst, designed shear walls in the house to resist simultaneous vertical and lateral forces. The shear-wall connections must resist intense loads that change direction every few seconds—the idea is not to prevent all damage, but to prevent the building from collapsing on occupants.
The first level of strengthening is the sheathing and its nailing pattern. Vertical plywood sheets nailed every 6 in. on the perimeter and every 12 in. in the field add lateral strength. To further strengthen the structure, reinforcements are added where walls are interrupted or change direction. In addition to the typical foundation bolts tying the sill to the foundation, Simpson Strong-Tie hold-downs are run vertically to connect framed walls to concrete stem walls and to connect the second-story walls to the first story. These same hold-downs are used horizontally along with metal strapping to reinforce the connection where the first-floor wall is interrupted by the projecting second-floor system.