Permissible Clear Spans for Rafters (to BS 5268-7.5)

Slope Imposed load Strength class Plasterboard
  • Find the column for your dead load and spacing, and the row for your timber size to find the permissible clear span on slope in metres.
  • Click on a span to generate a full calculation (you can adjust the exact span and slope).
  • This span table is to the format and methodology given in BS 5268-7.5.
  • These spans were calculated using our rafter calculation engine.
  • These span tables are the equivalent of other industry-standard span tables and are calculated to the same standards.
  • This table uses commonly available UK regularised timber depths.
  • Read the notes at the bottom of the table for assumptions, references and related standards.
Back BACK RAFTER CALCULATOR Equivalent purlin span table
C24
Dead load per square metre (in kN/m²) supported by rafters
Not more than 0.5 More than 0.5 but not more than 0.75 More than 0.75 but not more than 1
Centre-to-centre spacing of rafters (in mm)
Rafter size
Width × depth (mm)
400 450 600 400 450 600 400 450 600
Permissible clear span on slope (metres)
38 × 95 2.238 2.152 1.953 2.123 2.041 1.850 2.028 1.949 1.766
38 × 120 2.821 2.713 2.463 2.677 2.573 2.334 2.558 2.458 2.228
38 × 145 3.402 3.272 2.971 3.229 3.104 2.817 3.085 2.966 2.690
38 × 170 3.979 3.828 3.479 3.778 3.634 3.299 3.612 3.472 3.150
38 × 195 4.555 4.383 3.984 4.326 4.161 3.779 4.136 3.977 3.609
44 × 95 2.350 2.260 2.052 2.230 2.144 1.945 2.131 2.048 1.857
44 × 120 2.961 2.848 2.588 2.811 2.703 2.454 2.687 2.583 2.343
44 × 145 3.569 3.434 3.121 3.389 3.260 2.961 3.240 3.115 2.827
44 × 170 4.174 4.017 3.653 3.965 3.815 3.466 3.792 3.646 3.311
44 × 195 4.776 4.598 4.184 4.539 4.367 3.970 4.341 4.176 3.793
47 × 95 2.402 2.310 2.098 2.280 2.192 1.989 2.179 2.094 1.899
47 × 120 3.026 2.911 2.646 2.873 2.763 2.509 2.746 2.640 2.396
47 × 145 3.647 3.509 3.191 3.464 3.332 3.027 3.312 3.185 2.891
47 × 170 4.264 4.105 3.734 4.051 3.898 3.544 3.875 3.727 3.385
47 × 195 4.879 4.697 4.276 4.637 4.463 4.058 4.436 4.268 3.878
ALS/CLS
38 × 114 2.682 2.578 2.340 2.544 2.446 2.218 2.431 2.336 2.117
38 × 140 3.286 3.160 2.870 3.119 2.998 2.721 2.980 2.864 2.597
38 × 184 4.302 4.139 3.762 4.085 3.929 3.568 3.905 3.755 3.407