Technical Booklet D Structure·Page 47·Table 4B.32
Table 4B.32: Maximum clear span of purlins supporting rafters for roof pitch 30–45°
This table specifies the maximum clear span in metres for timber purlins of various sizes supporting rafters on roofs pitched between 30° and 45°, with an imposed load of 1.00 kN/m² and C16 timber strength class. Spans are given according to purlin spacing (1500–3000 mm) and dead load range.
Table 4B.32 Maximum clear span of purlins supporting rafters (m); Roof pitch more than 30° but not more than 45°; Imposed load of 1.00 kN/m²; Timber strength class C16 C16
Dead Load [kN/m²] excluding the self weight of the purlin
Size of purlin (mm) | 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
Design spacing of purlins (mm) | 1500 1800 2100 2400 2700 3000 | 1500 1800 2100 2400 2700 3000 | 1500 1800 2100 2400 2700 3000
47 x 150 | 1.87 | — | —
47 x 175 | 2.17 2.04 1.92 1.83 | 2.05 1.92 1.81 | 1.95 1.82
47 x 200 | 2.48 2.32 2.20 2.09 1.97 1.86 | 2.34 2.19 2.06 1.93 1.81 | 2.23 2.08 1.92
47 x 225 | 2.79 2.61 2.47 2.34 2.20 2.08 | 2.64 2.46 2.31 2.15 2.03 1.92 | 2.51 2.33 2.15 2.01 1.89
63 x 150 | 2.07 1.94 1.84 | 1.96 1.83 | 1.86
63 x 175 | 2.41 2.26 2.14 2.04 1.95 1.88 | 2.28 2.14 2.02 1.92 1.84 | 2.17 2.03 1.92 1.83
63 x 200 | 2.76 2.58 2.44 2.33 2.23 2.14 | 2.61 2.44 2.31 2.20 2.10 2.00 | 2.48 2.32 2.19 2.09 1.97 1.86
63 x 225 | 3.10 2.90 2.75 2.62 2.51 2.41 | 2.93 2.74 2.59 2.47 2.36 2.23 | 2.79 2.61 2.47 2.33 2.20 2.08
75 x 125 | 1.84 | — | —
75 x 150 | 2.20 2.07 1.96 1.86 | 2.08 1.95 1.85 | 1.98 1.86
75 x 175 | 2.57 2.41 2.28 2.17 2.08 2.00 | 2.43 2.28 2.15 2.05 1.96 1.89 | 2.31 2.17 2.05 1.95 1.87
75 x 200 | 2.93 2.75 2.60 2.48 2.38 2.29 | 2.77 2.60 2.46 2.34 2.24 2.16 | 2.64 2.47 2.34 2.23 2.13 2.04
75 x 225 | 3.29 3.09 2.92 2.79 2.67 2.57 | 3.12 2.92 2.76 2.63 2.52 2.43 | 2.97 2.78 2.63 2.50 2.40 2.28
2 x 47 x 200 | 3.31 3.11 2.95 2.82 2.70 2.60 | 3.14 2.95 2.79 2.66 2.55 2.46 | 2.99 2.81 2.66 2.54 2.43 2.34
2 x 47 x 225 | 3.72 3.50 3.32 3.17 3.04 2.93 | 3.53 3.31 3.14 2.99 2.87 2.76 | 3.36 3.16 2.99 2.85 2.73 2.63
2 x 47 x 250 | 4.13 3.88 3.68 3.51 3.37 3.25 | 3.91 3.68 3.48 3.32 3.19 3.07 | 3.73 3.51 3.32 3.17 3.04 2.92
2 x 47 x 275 | 4.53 4.26 4.05 3.86 3.71 3.57 | 4.30 4.04 3.83 3.65 3.50 3.37 | 4.10 3.85 3.65 3.48 3.34 3.21
2 x 47 x 300 | 4.94 4.65 4.41 4.21 4.04 3.89 | 4.68 4.40 4.17 3.98 3.82 3.68 | 4.47 4.20 3.98 3.79 3.64 3.50
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet D - Structure.pdf