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 1.896 1.874 1.813 1.813 1.786 1.714 1.744 1.714 1.634
38 × 120 2.593 2.556 2.458 2.458 2.414 2.301 2.349 2.301 2.180
38 × 145 3.314 3.261 3.120 3.120 3.058 2.900 2.966 2.900 2.734
38 × 170 4.051 3.979 3.694 3.791 3.711 3.472 3.591 3.506 3.293
38 × 195 4.795 4.648 4.230 4.468 4.368 3.977 4.219 4.114 3.773
44 × 95 2.029 2.004 1.937 1.937 1.907 1.828 1.861 1.828 1.741
44 × 120 2.766 2.726 2.618 2.618 2.571 2.448 2.499 2.448 2.317
44 × 145 3.527 3.468 3.314 3.315 3.249 3.078 3.149 3.078 2.900
44 × 170 4.300 4.223 3.878 4.021 3.934 3.646 3.806 3.714 3.460
44 × 195 5.059 4.873 4.439 4.731 4.589 4.176 4.464 4.353 3.963
47 × 95 2.091 2.065 1.995 1.995 1.964 1.881 1.916 1.881 1.791
47 × 120 2.847 2.805 2.693 2.693 2.643 2.516 2.569 2.516 2.380
47 × 145 3.625 3.565 3.387 3.406 3.337 3.161 3.234 3.161 2.977
47 × 170 4.416 4.335 3.963 4.127 4.038 3.727 3.905 3.811 3.538
47 × 195 5.166 4.977 4.536 4.852 4.688 4.268 4.578 4.455 4.051
ALS/CLS
38 × 114 2.423 2.390 2.301 2.301 2.262 2.159 2.202 2.159 2.048
38 × 140 3.169 3.118 2.986 2.986 2.928 2.780 2.842 2.780 2.623
38 × 184 4.467 4.384 3.995 4.170 4.078 3.755 3.942 3.846 3.562