Table 4B.20: Maximum clear span of purlins supporting rafters

Table 4B.20 Maximum clear span of purlins supporting rafters (m); Roof pitch more than 22.5° but not more than 30°; Imposed load of 0.75 kN/m2; Timber 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 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 Design spacing of purlins (mm): 1500, 1800, 2100, 2400, 2700, 3000 Table provides maximum clear spans in metres for each combination of purlin size, dead load, and spacing.