Permissible Clear Spans for Purlin Supporting Rafters (to BS 5268-7.6)

Slope Imposed load Strength class
  • 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 5268-7.6.
  • These spans were calculated using our purlin 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 PURLIN CALCULATOR Equivalent rafter span table
C16
Dead load per square metre (in kN/m²) supported by purlin
Not more than 0.5 More than 0.5 but not more than 0.75 More than 0.75 but not more than 1
Purlin spacing (in mm)
Purlin size
Width × depth (mm)
1500 1800 2100 2400 2700 3000 1500 1800 2100 2400 2700 3000 1500 1800 2100 2400 2700 3000
Permissible clear span (metres)
72 × 120                                    
72 × 145 2.164 2.030 1.921 1.831     2.030 1.902         1.922 1.800        
72 × 170 2.535 2.378 2.251 2.145 2.056 1.978 2.378 2.229 2.108 2.008 1.923 1.849 2.252 2.109 1.993 1.897 1.816  
72 × 195 2.905 2.725 2.580 2.459 2.357 2.268 2.726 2.555 2.417 2.302 2.205 2.120 2.581 2.417 2.285 2.175 2.082 1.993
72 × 220 3.274 3.072 2.909 2.773 2.657 2.557 3.073 2.880 2.725 2.596 2.486 2.391 2.910 2.726 2.577 2.453 2.348 2.233
72 × 245 3.643 3.418 3.237 3.086 2.958 2.846 3.419 3.206 3.033 2.890 2.767 2.661 3.238 3.034 2.869 2.731 2.608 2.471
95 × 120 1.974 1.853         1.853                      
95 × 145 2.382 2.237 2.120 2.022 1.939 1.867 2.237 2.099 1.988 1.895 1.816   2.120 1.988 1.881      
95 × 170 2.790 2.620 2.483 2.369 2.272 2.188 2.620 2.459 2.329 2.220 2.128 2.048 2.484 2.329 2.204 2.101 2.012 1.936
95 × 195 3.196 3.002 2.845 2.715 2.604 2.508 3.003 2.818 2.669 2.545 2.440 2.348 2.846 2.670 2.527 2.408 2.307 2.220
95 × 220 3.601 3.383 3.207 3.061 2.936 2.828 3.384 3.177 3.009 2.870 2.751 2.648 3.208 3.010 2.849 2.716 2.602 2.503
95 × 245 4.006 3.764 3.569 3.406 3.267 3.147 3.765 3.534 3.349 3.194 3.062 2.947 3.570 3.349 3.171 3.022 2.896 2.786