Tempo:
bracing of top chord plane, b) lateral web bracing and c) permanent bracing to web member or bottom chord plane. The stiffness of the roof is increased when the sheathing has been applied. Trusses must be installed and braced according to the manufacturer’s instructions and must not be cut or altered.
Site Assembly of Pitched Roofs For on-site construction, the gable roof is the simplest roof constructed with rafters or trusses (Figure 82), which are the same length and pattern and can be erected rather easily. Dormers may be added to provide additional light, headroom and ventilation (see Figure 88). The hip roof design uses common rafters fastened to a ridge board, with hip rafters providing the support for the jack rafters (Figure 83b).
Liveable attic spaces need adequate insulation, an air barrier system and a vapour barrier as discussed in Chapter 5. The size of framing members found in Tables 29 to 32 (pp. 295-301) may need to be increased to provide space for additional insulation to meet energy efficiency requirements, or additional wood framing may be added to increase the space in the roof cavity. Ceiling joists are used to support the ceiling finish and to act as ties between exterior walls and, in some cases, opposing rafters. They may also provide support for roof loads transferred to them by dwarf walls (knee walls) used as intermediate support for rafters, in which case they must be sized accordingly. (See Table 33 on p. 303 for ceiling joist spans.) When ceiling joists also support floor loads, determine what size is needed from the floor joist tables. (See Table 19 and Table 20 on pp. 283-285)
82 Types of pitched roofs
Flat
Monopitch
Gable
Hip
Gambrel
Mansard
Site Assembly of Pitched Roofs For on-site construction, the gable roof is the simplest roof constructed with rafters or trusses (Figure 82), which are the same length and pattern and can be erected rather easily. Dormers may be added to provide additional light, headroom and ventilation (see Figure 88). The hip roof design uses common rafters fastened to a ridge board, with hip rafters providing the support for the jack rafters (Figure 83b).
Liveable attic spaces need adequate insulation, an air barrier system and a vapour barrier as discussed in Chapter 5. The size of framing members found in Tables 29 to 32 (pp. 295-301) may need to be increased to provide space for additional insulation to meet energy efficiency requirements, or additional wood framing may be added to increase the space in the roof cavity. Ceiling joists are used to support the ceiling finish and to act as ties between exterior walls and, in some cases, opposing rafters. They may also provide support for roof loads transferred to them by dwarf walls (knee walls) used as intermediate support for rafters, in which case they must be sized accordingly. (See Table 33 on p. 303 for ceiling joist spans.) When ceiling joists also support floor loads, determine what size is needed from the floor joist tables. (See Table 19 and Table 20 on pp. 283-285)
82 Types of pitched roofs
Flat
Monopitch
Gable
Hip
Gambrel
Mansard
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