Tempo:
measured between the inside edges of the joist supports and have been calculated for standard Canadian lumber sizes. Strength requirements ensure the floor joist system is strong enough to support the anticipated loads. Deflection requirements ensure that the deformation of the floor under heavy load is within acceptable limits and will not lead to defects, such as cracking of the ceiling below the floor. Vibration requirements ensure that the floor is adequately stiff so that, for example, foot traffic will not cause dishes in cabinets to rattle. Dimension lumber floor joists are usually 38 mm (2 in. nominal) thick and either 140, 184, 235 or 286 mm (6, 8, 10 or 12 in. nominal) deep depending on the loading, span, spacing between joists, and species and grade of lumber.
Alternatives to dimension lumber floor joists include laminated veneer lumber (LVL) joists, parallel chord trusses and wood I-joists. Wood I-joists have become common residential floor framing materials because they can span longer distances and they shrink less because they are made from dry materials. Typical residential wood I-joists are 241 mm (91⁄2 in.) and 302 mm (117⁄8 in.) deep. Wood I-joists have special installation details (Figure 61) that differ from those for dimension lumber joists. Because of their thin webs, wood I-joists are less capable than lumber joists of supporting vertical loads (for example, from load-bearing walls above). For this reason, special blocking techniques are used to transfer vertical loads around and through the wood I-joists
61 Principles for wood I-joist installation proper storage and handling
adequate joist bearing length
correct span distance
rim framing to transfer continuous wall loads all wood I-joist cantilevers require engineering
squash blocks to transfer point loads
safe installation— bracing or sheathing correct placement and sizing of holes in webs
web stiffeners (where required) to transfer floor loads
Alternatives to dimension lumber floor joists include laminated veneer lumber (LVL) joists, parallel chord trusses and wood I-joists. Wood I-joists have become common residential floor framing materials because they can span longer distances and they shrink less because they are made from dry materials. Typical residential wood I-joists are 241 mm (91⁄2 in.) and 302 mm (117⁄8 in.) deep. Wood I-joists have special installation details (Figure 61) that differ from those for dimension lumber joists. Because of their thin webs, wood I-joists are less capable than lumber joists of supporting vertical loads (for example, from load-bearing walls above). For this reason, special blocking techniques are used to transfer vertical loads around and through the wood I-joists
61 Principles for wood I-joist installation proper storage and handling
adequate joist bearing length
correct span distance
rim framing to transfer continuous wall loads all wood I-joist cantilevers require engineering
squash blocks to transfer point loads
safe installation— bracing or sheathing correct placement and sizing of holes in webs
web stiffeners (where required) to transfer floor loads
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