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Strutting beams continued

Diagram showing a strutting beam within a section of a roof. The beam sits on a stud at the rafter end, and on a block on top of a stud to provide strutting beam support at the other end. There is 25 mm clearance at mid span of the strutting beam. A strut runs between the strutting beam and an underpurlin beneath the rafter. The thickness of the strutting beam for the majority of its length is 'D'. At the end it has been angle cut to match the slope of the rafter. The height of the vertical part is labelled '100 mm or D/3 whichever is the greater'.

The ends of strutting beams may be chamfered A chamfered edge is a shaped or bevelled edge connecting two surfaces. It is used to soften sharp edges and to improve fit. to avoid interference with the roof claddings. Where the end dimension is less than 100 mm or one-third of the beam depth, whichever is greater, an alternative support method must be provided. This support is similar to that shown for hanging beams.

Table 27 of AS 1684 provides details for maximum strutting beam support.



Diagram showing a section of a roof with ridgeboard, roof strut, strutting beam and underpurlin. The strutting beam span is marked as the horizontal distance from below the ridgeboard to the beginning of the eaves. The length of the ridgeboard is 'A'; the length of a rafter from the ridgeboard to the beginning of the eaves is 'B'. A formula states: Roof area supported ridge strutted = (1/2) A x (1/2) B. An area on the roof that is half of length A long and half of length B wide is shaded to illustrate this area.