|In addition to the issues of sustainability of wood production and use that were raised in Chapter 3, there are issues that pertain especially to wood light frame construction:¥ A wood light frame building can be designed to minimize waste in several ways. It can be dimensioned to utilizefull sheets and lengths of wood products. Most small buildings can be framed with studs 24 inches (610 mm) o.c. rather than 16 inches (406 mm). A stud can be eliminated at each corner by using small, inexpensive metal clips to support the interior wall Þ nish materials.
If joists and rafters are aligned directly over studs, the top plate can be a single member rather than a double one. Floor joists can be spliced at points of inß ection rather than over girders; this reduces bending moments and allows use of smaller joists. Roof trusses often use less wood than conventional rafters and ceiling joists.
¥ Laminated strand lumber and rim joists, wood I-joists, laminated veneer lumber beams and headers, glue-laminated girders, parallel strand lumber girders, and OSB
|sheathing are all materials that utilize trees more efÞ ciently than solid lumber. Finger-jointed studs made up of short lengths of scrap lumber glued together may replace solid full-length wood studs.¥ Framing carpenters can waste less lumber by saving cutoffs and reusing them rather than throwing them automatically on the scrap heap. In some localities, scrap lumber can be recycled by shredding it for use in OSB production. The burning of construction scrap should be discouraged because of the air pollution it generates.
¥ Although the thermal efÞ ciency of wood light frame construction is inherently high, it can be improved substantially by various means, as shown in Figures 7.17Ð 7.21. wood framing is much less conductive of heat than light-gauge steel framing. Steel framing of exterior walls is not a satisfactory substitute for wood framing unless the heat ß ow path through the steel framing members can be broken with a substantial thickness of insulating foam. loadbearing headers across the tops (Figure 5.32).
Sheathing, a layer of wood panels nailed over the outside face of the framing, is a key component of platform framing. The end nails that connect the plates to the studs have little holding power against uplift of the roof by wind, but the sheathing connects the frame into a single strong unit from foundation to roof.
The rectilinear geometry of the paralel framing members has no useful resistance to wracking by lateral forces such as wind, but rigid sheathing panels brace the building effectively against these forces. Sheathing also furnishes a surface to which shingles, boards, and ß ooring are nailed for Þ nish surfaces. In buildings constructed without sheathing, or with sheathing materials that are too weak to brace the frame, such as insulating plastic foam, diagonal bracing must be applied to the wall framing to impart lateral stability.