Wall bracing is needed to keep buildings from falling. Sheathing the exterior walls is a typical way to provide bracing. The architect, engineer, or whoever creates the plans will specify when any special bracing is needed. Although you don’t need to know everything about wall bracing, it is good to have a basic understanding of it.
Two common exceptions to these methods are:
(1) the short wall often used for garages, and
(2) the 24" wide corner wall. Note that cripple walls have their own requirements.
The IBC states that braced wall panels must be clearly indicated on the plans. However, this is not always the case in the real world. Although shear walls are usually marked on the plans, braced wall panels often are not.
The IBC and IRC contain a table that shows braced wall panel limitations and requirements.
The limitations are related to the seismic design category, and to how many stories are built on top of the walls.
Where braced wall lines rest on concrete or masonry foundations, they must have anchor bolts that are not less than W in diameter or a code-approved anchor strap. The anchor bolts or straps should be spaced not more than 6 apart (or not more than 4 apart if the building is over two stories).
Each piece of wall plate must contain at least two bolts or straps. There must be one between 4" and 12" from each end of each piece. A nut and washer must be tightened on each bolt. In IBC seismic design categories D, E, and F, engineered shear walls
Anchor Bolts
require 0.229” x 3" x 3" plate washers. In IRC seismic design categories D0, D^ D2, and E, braced walls require 0.229" x 3" x 3" plate washers. (See “Anchor Bolts" illustration.) These requirements also apply to townhouses in seismic design category C.
The eleven basic construction methods for braced wall panels are as follows:
1. LIB—Let-in-bracing
2. DWB—Diagonal wood boards
3. WSP—Wood structural panel
4. SFB—Structural fiberboard sheathing
5. GB—Gypsum board
6. PBS—Particleboard sheathing
7. PCP—Portland cement plaster
8. HPS—Hardboard panel siding
9. ABW—Alternate braced wall
10. PFH—Intermittent portal frame
11. PFG—Intermittent portal frame at garage
Ridge boards must be at least 1" nominal in width and must be as deep as the cut end of the rafter.
Hip and valley rafters must be at least 2" nominal and must be as deep as the cut ends of the rafters connecting to the hip of the valley. Gusset plates as a tie between rafters may be used to replace a ridge board.
Rafters must have a bearing surface similar to that of joists at their end supports. Bearing needs to be Ш" on wood or metal and not less than 3" on masonry or concrete.
Drilling and notching have the same limitations for rafters as they do for floor joists. (See “Rafter Drilling & Notching" illustration.)
To prevent rotation of rafter framing members, lateral support or blocking must be provided for rafters and ceiling joists larger than 2 x 10s.
Bridging must be provided for roofs or ceilings larger than 2 x 12. The bridging may be solid blocking, diagonal bridging, or a continuous 1" x 3" wood strip nailed across the ceiling joists or rafters at intervals not greater than 8′. Bridging is not needed if the ceiling joists or rafters are held in line for the entire length with, for example, sheathing on one side and gypsum board on the other.
When rafters are used to frame the roof, the walls that the rafters bear on must be tied together by a connection to keep them from being pushed out.
If these walls are not tied together, then the ridge board must be supported by or framed as a beam in order to support the ridge. Ceiling joists are typically used to tie the walls together. The ceiling joists must be tied to the rafters, the walls, and any lapping ceiling joists. (See ceiling joists.)
