Technical Booklet D Structure·Page 44·Table 4B.26
Maximum clear span of purlins supporting rafters
Table 4B.26 provides maximum clear span values in metres for timber purlins of various sizes supporting rafters on roofs pitched between 22.5° and 30°, with an imposed load of 1.00 kN/m² and varying dead loads. Spans vary based on purlin size, design spacing, and dead load category.
Table 4B.26 Maximum clear span of purlins supporting rafters (m); Roof pitch more than 22.5° but not more than 30°; Imposed load of 1.00 kN/m2; Timber strength class C24
Dead Load [kN/m2] excluding the self weight of the purlin, with design spacing of purlins (mm) at 1500, 1800, 2100, 2400, 2700, 3000.
Purlin sizes: 47 x 150, 47 x 175, 47 x 200, 47 x 225, 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.
Dead load categories: Not more than 0.50 kN/m², More than 0.50 but not more than 0.75 kN/m², More than 0.75 but not more than 1.00 kN/m².
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet D - Structure.pdf