Technical Booklet D Structure·Page 38·Table 4B.14
Table 4B.14: Maximum clear span of purlins supporting rafters
This table specifies the maximum clear spans in metres for timber purlins of various sizes supporting rafters. The table applies to roof pitches between 15° and 22.5°, an imposed load of 0.75 kN/m², timber strength class C24, and various dead loads and purlin spacings.
Table 4B.14 Maximum clear span of purlins supporting rafters (m); Roof pitch more than 15° but not more than 22.5°; Imposed load of 0.75 kN/m2; Timber strength class C24 C24
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
For three 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
For design spacing of purlins: 1500, 1800, 2100, 2400, 2700, 3000 mm
Spans range from 1.82 m to 5.12 m depending on purlin size, dead load, and spacing.
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