Wind-resistant Walls

Claudette Reichel  |  7/23/2008 9:18:59 PM

Figure 1, Stud-to-plate and Plate-to-foundation Connections

Figure 2, Story-to-story Connection and Structural Sheathing

Figure 3, Narrow Wall Bracing

Figure 4, Corner Hold Downs

Wall strength

For wood frame construction: The wood species used for framing should have a specific gravity greater than 0.49. Examples are Southern Pine, Douglas Fir-Larch, Hem-Fir, Red Oak and mixed Maple. Lumber 2x4 wall studs should be spaced 16 inches on center (o.c.); 2x6 studs can be spaced 24 in. o.c.

Plate-to-foundation connection: The sill or bottom plate of walls should be secured to the foundation with 5/8-inch anchor bolts (and 3x3-inch washers), embedded 7 inches in solid concrete foundation or 18” in a block stemwall. Bolts in stemwalls with frame floors should be spaced every 4 feet (or to code tables) and at all corners and wall openings. For slabs, bolts should be spaced closer, typically 18-24 in. apart. (Figure 1, Plate-to-foundation Connection)

Stud-to-plate connection: Each stud must be connected to the anchored bottom plate and to the top plates to resist the code specified uplift load; this may be achieved with hurricane hardware or with specially sized and installed structural sheathing that extends continuously from bottom plate to top plate. (Figure 1, Stud-to-plate Connection)

Story-to-story connection: Upper and lower stories of wall framing must be tied together. This is typically done with long metal strapping used every 4 feet or specially installed and nailed sheathing. (Figure 2, Story-to-story Connection)

Structural sheathing and shear walls: Exterior walls and interior load-bearing walls need sufficient reinforcement to resist wind shear (racking) and lateral forces on the house. Full structural sheathing of exterior walls is recommended; typically 7/16” or 15/32” plywood or OSB. Blocking is required to provide framing behind all panel seams; nail spacing of 6 in. may meet shear loads, closer when the sheathing is used for both shear and uplift loads.  (Figure 2, Structural Sheathing) 

Narrow wall segments next to large openings (particularly garage doors) may require commercial engineered shear wall segments for increased lateral resistance. When designing your home, try to avoid placing window and doors near corners.  (Figure 3, Narrow Wall Bracing)

Corner hold-downs: Additional hardware called “hold-downs” are needed at the ends of each wall segment (typically at each outer corner of the house) to prevent tip-over and resist the higher forces created when wind flows around a corner. If installed on a properly nailed 3-stud corner, one hold-down can serve both walls.  (Figure 4, Corner Hold Downs)

For masonry construction: Concrete block walls should be connected to the foundation with full-height steel rebar reinforcement at least every 4 feet. Vertical rebar reinforcement is also needed at all corners and both sides of openings.

For SIPS, ICF, ISPS and other building systems: The manufacturer or an engineer should verify that the building system is engineered and attached for your design wind speed. As with any building system, installation according to manufacturer’s or design specifications is essential.

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