Once the stud size and spacing and the framing system have been selected, it is time to consider how to brace the building to resist the forces of wind, earthquakes, and eccentric loading. Will diagonal bracing be adequate, or should the building be braced with structural sheathing and/or shear walls? This question is best answered in the context of the design of the building as a whole, considering the other materials that complete the wall system. How is the wall to be insulated? Where are the openings in the wall for doors and windows? Will there be an air-infiltration barrier? What material will be used for the exterior finish? The details relating to these issues are addressed in this chapter, along with some suggestions for their appropriate use. How these various details are assembled into a complete wall system depends on local climate, codes, tradition, and the talent of the designer.
sizing headers
Headers are structural members over openings in walls for windows or doors. Header size depends on wood species and grade, loading, header design, and roughopening span. Following is a rule of thumb for sizing a common header type, the 4x header (see 68B):
For a single-story building with a 30-lb. live load on the roof and 2×4 bearing walls, the span in feet of the rough opening should equal the depth (nominal) in inches of a 4x header. For example, openings up to 4 ft. wide require a 4×4 header and up to 6 ft. wide, a 4×6 header.
advanced framing
Advanced framing minimizes the amount of structural material that is required to hold up the building. The greatest impact on framing efficiency can be made in the walls because wall construction has evolved in such a way that the typical wall is overbuilt. Floors and roofs are constructed reasonably efficiently because the design challenge has been to span horizontally with an economy of materials. Standard framed walls, however, contain numerous extraneous and oversized elements. The elimination and downsizing of wall members not only saves lumber, it also lowers the effect of thermal bridging, thus saving energy. Advanced framing of walls is discussed in this chapter (see 74-76).
