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100 to 150 mm (4 to 6 in.) from the end of each piece. Locate butt joints in each member over a supporting post or within about 150 mm (6 in.) of the quarter points in the span. (See Tables 15 to 17 on pp. 277-280) Joints are not permitted in either the end spans or in not more than half the members at any one location. Bolts at least 12.7 mm (1⁄2 in.) in diameter and spaced not less than 1.2 m (4 ft.) apart can also be used to laminate a wood beam. Alternatives to built-up wood beams and columns include steel or glue-laminated timber (glulam) (Table 19 on p. 283) laminated veneer lumber (LVL) beams, and parallel strand lumber (PSL). Ends of beams must bear at least 89 mm (31⁄2 in.) on concrete or masonry walls or columns. To prevent deterioration, the ends of wood beams, located at or below grade and framed into masonry or concrete walls, must be treated to prevent decay or have
a 12 mm (1⁄2 in.) air space at the ends and sides. Untreated wood beams should also be separated from the concrete with an impermeable membrane if they are 150 mm (6 in.) or less above grade.
BEAM AND JOIST INSTALLATION Joists can rest on top of the beam (Figure 53), in which case the top of the beam is level with the top of the sill plate (Figure 52). This method is used where the basement has adequate headroom below the beam. The joists should lap above the beam and the maximum recommended length of lap is 300 mm (12 in.). Where more clearance under a wood beam is desired, the beam may be installed flush with the joists, which are then supported by joist hangers or other structural connectors attached to the beam. Joists can also be supported on ledger strips attached to wood beams
53 Joists supported on top of wood beam
built-up wood beam
wood joist toenail metal or wood column