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
C16
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 1.722 1.702 1.650 1.650 1.626 1.563 1.590 1.563 1.493
38 × 120 2.363 2.331 2.245 2.245 2.207 2.097 2.149 2.107 1.957
38 × 145 3.031 2.984 2.714 2.859 2.804 2.509 2.722 2.663 2.343
38 × 170 3.715 3.575 3.154 3.483 3.362 2.916 3.303 3.145 2.724
38 × 195 4.256 4.093 3.589 4.040 3.825 3.320 3.792 3.579 3.101
44 × 95 1.845 1.823 1.765 1.765 1.739 1.670 1.699 1.670 1.593
44 × 120 2.525 2.489 2.395 2.395 2.353 2.244 2.290 2.244 2.108
44 × 145 3.230 3.178 2.913 3.042 2.983 2.699 2.894 2.831 2.522
44 × 170 3.901 3.753 3.389 3.699 3.562 3.137 3.505 3.379 2.932
44 × 195 4.465 4.296 3.856 4.240 4.078 3.570 4.054 3.845 3.338
47 × 95 1.902 1.880 1.819 1.819 1.792 1.719 1.750 1.719 1.639
47 × 120 2.600 2.563 2.465 2.465 2.421 2.308 2.356 2.308 2.179
47 × 145 3.322 3.268 2.978 3.127 3.066 2.788 2.974 2.908 2.607
47 × 170 3.986 3.835 3.486 3.785 3.641 3.241 3.599 3.480 3.030
47 × 195 4.561 4.390 3.981 4.333 4.169 3.688 4.144 3.970 3.449
ALS/CLS
38 × 114 2.207 2.178 2.100 2.100 2.066 1.975 2.013 1.975 1.864
38 × 140 2.896 2.852 2.625 2.735 2.684 2.427 2.607 2.551 2.266
38 × 184 4.019 3.865 3.398 3.815 3.622 3.143 3.590 3.389 2.935