How to Design a Plywood Shear Wall for Wood Frame Building
Shear walls consist of wood framing covered with structurally rated sheathing, either orient-strand board (OSB) or plywood. When properly constructed and located, the shear wall increases the stability of the building by resisting uplift forces and forces imposed along the length of the wall. As the mechanics of seismic stress in buildings have become better understood, building codes, such as the International Residential Code, increasingly call for shear wall construction in residential buildings.
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Things You'll Need
- 2x4 lumber
- Structural panels rated "Structural 1," either plywood or OSB
- Large and small carpenter's squares
- 4-foot level and small level
- Tape Measure
- Hammer
- Nail gun (optional)
- Structural hardware (optional, unless specified by a structural engineer)
- Illustrated framing guide with shear wall discussion, published 2004 or later
Instructions
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Assess the complexity of your building to determine whether you can design your shear walls yourself or if you should consult a structural engineer to develop the shear wall design. If you have a good working knowledge of building construction, you can safely design shear walls for a smaller rectangular one-story or two-story building situated on relatively flat ground in an area without a history of earthquakes. If you do not have such knowledge or your building project exceeds these limits, you should consult a structural engineer. No one lacking a structural engineering degree should attempt to design shear walls for a building in which wall length exceeds 75 feet.
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Locate exterior shear walls from the foundation upward to the roof, including crawl spaces. The building design should include continuous footings underneath all shear walls. Shear walls should align from story to story. If your building design includes stories that do not continuously vertically align, consult a structural engineer.
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Implement shear wall design with adequately dimensioned lumber. Use a minimum of 2x4 studs on 16-inch centers throughout. Many residential buildings use 2x6 studs. Consult a contemporary framing guide to ensure that the wood framing supporting your shear panels provides adequate strength and stability.
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Use five-eighths-inch thick 4x8 or 4x10 structural panels ("sheathing") -- labeled "Structural 1" on the face of the plywood or OSB -- on the framing. Use 16d (16 penny), 3 1/2-inch common nails that fully penetrate studs and plates. Most shear panel designs call for nails on 12-inch centers from floor plate up along the stud and into the top plate. Some shear panel designs may require nails on 6-inch centers. If in doubt, consult a structural engineer.
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Use hold-down hardware (available at larger home-improvement centers) to secure the floor plates of shear panels to the underlying frame. Use anchor bolts and threaded rod embedded in concrete footings with structural epoxy to tie the shear panel to the foundation. Consult a recently published framing guide to determine which hardware types your structure requires.
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Tips & Warnings
Good shear wall design incorporates elements that increase structural stability by resisting largely horizontal forces along the wall's length and the uplift forces in an earthquake that tend to lift and rotate the building off its foundation or even tip the wall over entirely. Safe shear walls require good framing design and construction, consistent shear nailing and appropriate and liberal use of the metal fittings that tie the structural components together.
Do not guess at shear panel requirements. Contemporary framing books for nonengineers will provide more details and specifics to help you design and build safe shear walls.
References
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