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Table 29 — Rafters or Purlins

AS 1684.2
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Inputs

Timber Grade
Span Type
For MGP grades, sizes 240mm and 290mm deep use Sheet Roof (first button) / Tile Roof (second button) rather than Single/Continuous span type.
Roof Mass (kg/m²)
Rafter Spacing (mm)

Maximum Rafter or Purlin Span & Overhang

AS 1684.2 Table 29 — Wind classification N1/N2

Size (D×B mm)Max Span (mm)Max Overhang (mm)
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Design Reference

Figure 7.26/7.27 — Rafters and Purlins design parameters
Figures 7.26 & 7.27 — Rafters/Purlins: coupled roofs and cathedral/non-coupled roofs (AS 1684.2:2021)

Notes (AS 1684.2 Table 29):

i) Maximum spans are based on the support of roof mass only for a coupled roof and the combined roof plus ceiling mass for a cathedral roof.

ii) Allowable overhangs are based on a maximum depth of birdsmouth of D/3. Refer Figure 7.28.

iii) Where rafters are not birdsmouthed, the allowable overhang may be increased to 30% of the allowable single span for that member. Overhang shall not exceed 50% of actual backspan.

iv) Overhang limits do not apply where rafter ends are tied back to wall frame.

v) Wind classification N1/N2 only.

vi) For MGP10/12/15: sizes 240mm and 290mm deep use Sheet Roof / Tile Roof grouping rather than Single / Continuous span type.