The traditional cut roof

Refer now to Fig. 8.21. On traditionally constructed roofs little temporary bracing is required if the purlins are well fixed at their support points. This means of course ensuring that supporting brickwork has not only been constructed but that the cement mortar is adequately cured, otherwise damage to the wall could occur from the movements of constructing the roof above it. Although the illustration shows the trussed rafter roof detailed in Chapter 6, the essentials of bracing of course remain the same in any roof form. No specific guidance exists for the bracing of traditional roofs, but the recommendations laid down in BS 5268: Part 3 for trussed rafter roofs could well be followed with few modifications.

It is advisable to fit the diagonals B, the binders G being replaced by the ridge board and the ceiling joist binders themselves. Stability bracing can be achieved by adding diagonal brace F with brace J being fitted from the binder diagonally across the hangers to the purlin. Because the hangers may well be spaced further apart than with a trussed rafter system this member should be more substantial, probably 50 mm x 100 mm in section. If the purlin strut is used as illustrated in Fig. 3.4 this additional brace will not be required. Brace H in Fig. 8.21 is of course the purlin itself in a traditional roof. Finally the ceiling joist diagonal brace K should be fitted as indicated.

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