Engineering and Construction

In wood light frame structures constructed with  advanced framing techniques (also called optimum value engineering), special attention is given to minimizing the use of redundant or structurally unnecessary wood members, thereby reducing the amount of lumber required to construct the frame and, once the frame is insulated, increasing its thermal efficiency (Figure 5.64). A variety of techniques may be used, including:

Spacing framing members at 24 inches (610 mm) rather than 16 inches (406 mm) o.c.: Wider spacing of framing members reduces the amount of lumber required. In exterior walls,  thermal efficiency is also improved by the reduction in thermal bridging area in comparison to walls framed with more closely spaced members.

Designing to a 24-inch (610-mm) module: When the outside dimensions of a framed structure conform  to a 24-inch module, sheathing panel waste is minimized. Planning rough opening sizes and locations in floors,  walls, and roofs to conform, where possible, to modular dimensions can  reduce waste even further.

Designing to modular dimensions also reduces wastage of interior wallboard.

Using single top plates in all walls, both bearing and nonbearing: In the  case of bearing walls, this requires  floor or roof framing members to align directly over studs in the walls  that support them.

Figure 5.64 Comparison of walls framed with  conventional and advanced techniques. Wall A is framed . Studs are spaced at 16 inches (406 mm) o.c., the layout  of the wall and its openings is not coordinated with the framing module,  and standard details are used for corners, openings, and other features.  In wall B, studs are spaced at 24 inches (610 mm) o.c., the length of the wall and the location and size of its openings have  been coordinated to the greatest extent possible with the 24-inch module, and redundant framing members have been eliminated. Note that with the single top plate, fl>oor joists or roof rafters (shown dashed in these figures) bearing on wall B must fall directly over studs below. The total length of framing lumber used in  wall B is half of that required for wall A. Though only a foot and a half shorter in  length, wall B also can be sheathed with five standard-sized sheathing panels, whereas wall A requires six. Even if  wall A is constructed of 2 X 4 studs and wall B is constructed of 2 X 6 studs, the  overall savings in materials and reduction in waste in wall B are substantial.

Minimizing  other  unneeded framing members: Don't use headers over openings in nonbearing walls,  since they are not needed; in bearing walls, use headers only as deep as  required for the loads and span.  Where corner studs serve only to provide nailing surfaces or support  for wallboard, use other, less waste- ful blocking techniques or metal clips  designed for this purpose instead. Replace jack studs supporting headers at window and door openings with metal hangers; eliminate unneeded cripple studs under rough  sills. All of these techniques save lumber and, in exterior walls, increase energy efficiency by reducing thermal bridging through solid framing members.

Eliminating unneeded plywood and OSB wall sheathing: Where let-in bracing is structurally adequate  for lateral force resistance, eliminate structural panel wall sheathing entirely and cover walls with insulating  sheathing for better thermal efficiency. Where structural panels are required, use the minimum extent of  panels necessary.

Advanced framing techniques rely on unconventional framing methods and significantly  reduce  redundancy in the building frame. For these reasons, they should not  be used without guidance from a  structural engineer or other qualified design professional, and special review and approval from local building authorities may be required. Nevertheless, where these techniques  are used, significant benefits can be realized. According to the National Association of Home Builders Partnership for Advancing Technology in Housing, advanced framing techniques can reduce the amount of  lumber used in a wood light frame  structure by up to 19 percent and  improve the energy efficiency of the insulated structure by as much as 30 percent.