Tempo:
The additional roof load imposed by dwarf walls that run at right angles to ceiling joists (Figure 84) must be considered when choosing the size of the joists. An increase in the depth of the joists to the next standard depth will usually provide the additional strength required where the roof slope is more than 1:4. When the slope is 1:4 or less, determine the size of the ceiling joists from the span tables for roof joists (Tables 29 and 30 on pp. 295-297).
Since hip rafters are usually about 51 mm (2 in.) deeper than common or jack rafters, they reduce the space along the end walls to the extent that in low-slope roofs, there may not be enough room to install the outside ceiling joist at normal spacing from the wall. In this case, doubled joists are used and positioned to suit the available space (Figure 85). Tail joists are then added and toenailed to the outside wall plate and end-nailed
84 Rafter heel supported on a rafter plate Rafter plate nailed to top of each ceiling joist with at least two 100 mm (4 in.) nails rafter plate
ridge beam
rafter
exterior wall knee wall with top and bottom plates and stud in line with each ceiling joist and rafter struts at 1.2 m (4 ft.) o.c. ceiling joists lapped directly above interior load-bearing wall
85 Doubled ceiling joists and stub joists used where a hip rafter reduces clear space near the end wall jack rafter
hip rafter at least 50 mm (2 in.) deeper than jack rafters ceiling joist double ceiling joist normal location for ceiling joist if space is available stub joist end wall framing top plate
Since hip rafters are usually about 51 mm (2 in.) deeper than common or jack rafters, they reduce the space along the end walls to the extent that in low-slope roofs, there may not be enough room to install the outside ceiling joist at normal spacing from the wall. In this case, doubled joists are used and positioned to suit the available space (Figure 85). Tail joists are then added and toenailed to the outside wall plate and end-nailed
84 Rafter heel supported on a rafter plate Rafter plate nailed to top of each ceiling joist with at least two 100 mm (4 in.) nails rafter plate
ridge beam
rafter
exterior wall knee wall with top and bottom plates and stud in line with each ceiling joist and rafter struts at 1.2 m (4 ft.) o.c. ceiling joists lapped directly above interior load-bearing wall
85 Doubled ceiling joists and stub joists used where a hip rafter reduces clear space near the end wall jack rafter
hip rafter at least 50 mm (2 in.) deeper than jack rafters ceiling joist double ceiling joist normal location for ceiling joist if space is available stub joist end wall framing top plate
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