Engineering and Construction

Wall framing, like floor framing, is laid out in such a way that a framing member, in this case a stud, occurs under each vertical joint between sheathing panels (Figures 5.29-5.32). The  lead carpenter initiates wall framing by laying out the stud locations on the  top plate and sole plate of each wall. Other carpenters follow behind to cut the studs and headers and assemble the walls in a horizontal position  on the subfloor. As each wall frame is completed, it is tilted up and nailed into position, with temporary bracing  as needed (Figures 5.34-5.37).

Figure 5.29 Typical ground-floor wall framing details, keyed by letter to Figure 5.30.

Figure 5.30 Step Four in erecting a platform frame building: The ground-floor walls are framed. The letters A, B, and C indicate portions of the framing that are detailed in Figure 5.29.

Figure 5.31 Framing details for nonloadbearing interior partitions.

Figure 5.32 Steps in the framing of a typical wall and details at wall intersections and a window opening. In D, the short studs above the header and below the rough sill are called trimmer or cripple studs.

Figure 5.33 As the fi rst step in constructing a wall frame, the chief carpenter aligns the top plate and sole plate side by side on the floor platform and marks each stud location on both of them simultaneously with a pencil and framing square.

Figure 5.34 Nailing studs to a plate, using a pneu- matic nail gun. The triple studs are for a partition intersection.

Figure 5.35 Tilting an interior partition into position. The gap in the upper top plate will receive the projecting end of the upper top plate from another partition that intersects at this point.

Figure 5.36 Fastening a wall to the floor platform. Horizontal blocking between studs as seen toward the left in this photo is typically installed to provide a solid substrate for the later attachment of bathroom hardware, exterior panels, or any number of possible other items.

Figure 5.37 Lower-level wall framing is held up by temporary diagonal bracing until the floor joist framing is in place above and wall bracing or sheathing is complete, after which the frame becomes completely self-bracing. The outer walls of this building are framed with 2 x 6 (38 x 140 mm) studs to allow for a greater thickness of thermal insulation, whereas the interior partitions are made of 2 x 4 (38 x 89 mm) stock.

Figure 5.38 Prefabricated shear wall panels are especially useful in garage wall framing or other walls with large openings where only narrow, solid sections of wall remain to resist lateral forces. They may be made of all wood components or, where even greater strength is required, of wood and metal, as shown here. The corrugated galvanized steel in this panel is over 1/ 8  inch (3.5 mm) thick, and the panel’s capacity to resist lateral forces is several times greater than that of comparable all-wood prefabricated panels. The bottom of the panel will be anchored with bolts embedded 21 inches (533 mm) or more into the concrete foundation, and the sides and top will be screw-fastened to the surrounding wood framing. Holes in the panel can accommodate wiring runs within the wall.

Long studs for tall walls often must be larger than a 2 X 4 in order  to resist wind forces. Because long  pieces of sawn dimension lumber tend not to be straight and may be less  readily available, studs manufactured  of structural composite lumber may  be used instead. The International Residential Code requires horizontal  wood blocking to be installed between studs at midheight in wall frames that are taller than 10 feet (3 m). The purpose of this blocking is to stop off the cavities between studs to restrict the  spread of fire.

Headers over window and door openings must be sized in accordance  with building code criteria. Typically,  a wall opening header consists of two nominal 2-inch members standing on  edge, separated by a plywood spacer  that serves to make the header as  thick as the depth of the wall studs.  Headers for long spans and/or heavy loads are often made of laminated  veneer lumber or parallel strand lumber, either of which is stronger and stiffer than dimension lumber. Several manufacturers market prefabri- cated headers that include thermal insulation as a way of reducing the heat loss that occurs through these difficult-to-insulate assemblies. At either end, headers rest on shortened studs called trimmer or jack studs, which  themselves are nailed to full-height king studs. At the bottom of a window  opening, the  rough sill is supported  on cripple studs (Figure 5.32).

Each corner and partition intersection must furnish nailing surfaces for the edge of each plane of exterior  and interior finish materials. This requires a minimum of three studs  at each intersection, unless special  metal clips are used to reduce the number to two (Figure 5.32).

Sheathing was originally made of solid boards, usually 6 to 10 inches  (150 to 250 mm) wide. If applied  horizontally, these boards did little  to brace the building against wracking caused by the forces of wind or
earthquake. If applied on a diagonal, however, they produced a rigid frame. Today, walls are sheathed with  either plywood or OSB, which provide permanent, very stiff bracing, or with let-in bracing  as described below. Panels are applied as soon as possible after the wall  is framed, often while it is still lying on the floor platform.

In regions of strong winds or earthquakes, wall sheathing plays  a very important part in the lateral stability the structure. A properly sheathed wall acts as a  shear wall to  resist lateral forces. Both interior and  exterior walls can act as shear walls,  which must be provided in both east west and north-south orientations  and must be distributed more or less symmetrically in the floor plan. Stresses within shear walls are proportional  to their length, with shorter walls being subjected to higher stresses than those that are longer. Where walls have large openings for windows or doors, the remaining solid portions  that can contribute to lateral force resistance may become relatively short and therefore exposed to very  high stresses. In such cases, sheathing may have to be attached with  larger nails at very close spacings, the  horizontal edges of sheathing panels  may have to be supported by wood  blocking to keep them from buckling, and studs over which sheathing panels join may need to be larger in  size, such as 3 x or 4 x (64 mm or 89 mm) members, in order to hold  the required nails without splitting.

Where the needed strength cannot  be reliably achieved using site-con- struction methods, factory-fabricated  panels made of wood or steel com- ponents may be used (Figure 5.38).  Shear walls subject to high forces may also require hold-downs to prevent the  walls from pulling up off the foundation or floor platform (Figures 5.39-5.41). Consultation with a structural engineer is recommended (and often  legally required) when building in areas that are earthquake-prone or subject to very high wind forces.

Sheathing panels made from wood or paper fiber, plastic foam, and glass fiber are intended principally as  thermal insulation and to provide a base for water-resistant building paper or house wrap. Most panels of these types are nonstructural, so walls sheathed with such panels rely on  letin diagonal bracing or strategically located structural panels for lateral force  resistance. Let-in bracing may be made  of wood members, such as 1 x 4 (19 x 89 mm) boards, or light steel members that are recessed into the outer  face of the studs of the wall before it is sheathed (Figures 5.32 and 5.42).

Figure 5.39 Strap tie hold-downs are made of galvanized steel straps with hooked or deformed ends cast into the concrete foundation wall (top). After the wall is framed, the exposed length of strap may be nailed directly to framing or, as seen here, nailed through the sheathing into the studs or posts behind (bottom). The number, size, and spacing of nails used to fasten the strap depend on the magnitude of the loads that must be resisted and the capacity of the wood member to hold nails without splitting. In the top image, anchor bolts cast into the top of the foun- dation wall that will be used to secure the sill plate in place are also visible.

Figure 5.40 Hold-downs made from threaded rod and steel plate anchors can resist much greater forces than strap tie hold-downs. They may be used at each floor level to securely tie the full height of the building frame to its foundation. For the type shown here, the nuts at the ends of the threaded rods may require retightening after the fi rst heating season to compensate for wood shrinkage, which can mean that access holes must be provided through the interior wall surfaces. Other models rely on spring-loaded tapered shims or other mechanical compensation so as to be self-adjusting

Figure 5.41 A heavy-duty seismic hold-down similar to that illustrated in Figure 5.40. The anchor rod with one end cast into the concrete foundation wall protrudes through the preservative-treated wood sill where its threaded end is bolted to the anchor. The anchor in turn is bolted to a 4 4 (89 89 mm) post with fi ve bolts of substantial diameter. A conventional foundation anchor bolt with an oversized square washer is also partially visible to the right of the hold-down. Also note the thicker-than-normal, 3-inch nominal (64-mm) sill plate, a common feature in wood light framing designed for high seismic forces.

Figure 5.42 Applying a panel of insulating foam sheathing. Because this type of sheathing is too soft and weak to brace the frame, diagonal bracing is inserted into the outside faces of the studs at the corners of the building. Steel bracing, nailed at each stud, is used in this frame and is visible just to the right of the carpenter’s leg.