Technical Booklet D Structure·Page 45·Table 4B.28
Table 4B.28: Maximum clear span of purlins supporting rafters
This table provides maximum clear spans in metres for timber purlins of various sizes supporting rafters at roof pitches between 30° and 45°, with an imposed load of 0.75 kN/m² and timber strength class C16, varying by dead load and purlin spacing.
Table 4B.28 Maximum clear span of purlins supporting rafters (m); Roof pitch more than 30° but not more than 45°; Imposed load of 0.75 kN/m2; Timbers strength class C16 C16
Dead Load [kN/m2 ] excluding the self weight of the purlin
Size of purlin (mm): 47 x 150, 47 x 175, 47 x 200, 47 x 225, 63 x 125, 63 x 150, 63 x 175, 63 x 200, 63 x 225, 75 x 125, 75 x 150, 75 x 175, 75 x 200, 75 x 225, 2 x 47 x 200, 2 x 47 x 225, 2 x 47 x 250, 2 x 47 x 275, 2 x 47 x 300
Design spacing of purlins (mm): 1500, 1800, 2100, 2400, 2700, 3000
Dead load categories: Not more than 0.50; More than 0.50 but not more than 0.75; More than 0.75 but not more than 1.00
Spans range from 1.83 m to 5.21 m depending on purlin size, spacing, and dead load.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet D - Structure.pdf