Permissible Clear Spans for Flat Roof Joists (to BS 5268-7.2)

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 in metres.
  • Click on a span to generate a full calculation (you can adjust the exact span).
  • This span table is to the format and methodology given in BS 5268-7.2.
  • These spans were calculated using our flat roof joist 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 FLAT ROOF JOIST CALCULATOR
C16
Dead load per square metre (in kN/m²) supported by joists
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 joists (in mm)
Joist size
Width × depth (mm)
400 450 600 400 450 600 400 450 600
Permissible clear span (metres)
38 × 95 1.693 1.674 1.623 1.623 1.600 1.538 1.564 1.538 1.470
38 × 120 2.326 2.294 2.210 2.210 2.173 2.075 2.116 2.075 1.969
38 × 145 2.984 2.938 2.717 2.816 2.762 2.578 2.682 2.624 2.462
38 × 170 * 3.645 3.505 3.182 3.432 3.329 3.019 3.256 3.180 2.884
38 × 195 * 4.173 4.014 3.645 3.966 3.813 3.459 3.793 3.645 3.305
38 × 220 * 4.700 4.521 4.107 4.467 4.295 3.898 4.273 4.107 3.725
44 × 95 1.815 1.794 1.737 1.737 1.712 1.644 1.672 1.644 1.569
44 × 120 2.485 2.451 2.358 2.358 2.317 2.211 2.255 2.211 2.096
44 × 145 3.180 3.130 2.856 2.997 2.939 2.710 2.852 2.789 2.590
44 × 170 3.826 3.680 3.343 3.636 3.496 3.174 3.455 3.343 3.033
44 × 195 * 4.379 4.213 3.830 4.163 4.003 3.636 3.983 3.830 3.475
44 × 220 * 4.930 4.744 4.314 4.688 4.510 4.097 4.486 4.314 3.916
47 × 95 1.872 1.850 1.790 1.790 1.764 1.693 1.723 1.693 1.615
47 × 120 2.559 2.523 2.421 2.427 2.385 2.274 2.320 2.274 2.155
47 × 145 3.271 3.215 2.920 3.081 3.021 2.772 2.931 2.866 2.649
47 × 170 3.909 3.761 3.418 3.716 3.574 3.245 3.548 3.418 3.102
47 × 195 * 4.474 4.305 3.915 4.254 4.091 3.718 4.070 3.915 3.554
47 × 220 * 5.036 4.847 4.410 4.790 4.609 4.189 4.585 4.410 4.003
63 × 95 2.140 2.114 2.041 2.041 2.009 1.924 1.960 1.924 1.831
63 × 120 2.909 2.865 2.671 2.751 2.700 2.536 2.624 2.570 2.425
63 × 145 3.677 3.539 3.220 3.474 3.365 3.059 3.300 3.220 2.925
63 × 170 4.298 4.138 3.768 4.090 3.936 3.580 3.916 3.768 3.424
63 × 195 4.915 4.734 4.313 4.679 4.505 4.100 4.482 4.313 3.922
63 × 220 5.529 5.327 4.856 5.265 5.070 4.617 5.045 4.856 4.418
72 × 120 3.078 3.032 2.792 2.908 2.854 2.652 2.772 2.714 2.536
72 × 145 3.838 3.696 3.365 3.653 3.516 3.198 3.478 3.365 3.059
72 × 170 4.485 4.320 3.936 4.270 4.111 3.742 4.090 3.936 3.580
72 × 195 5.127 4.940 4.505 4.883 4.703 4.284 4.679 4.505 4.100
72 × 220 5.764 5.556 5.070 5.493 5.292 4.823 5.265 5.070 4.617
ALS/CLS
38 × 89 1.547 1.530 1.486 1.486 1.466 1.412 1.435 1.412 1.352
38 × 114 2.171 2.143 2.067 2.067 2.033 1.945 1.982 1.945 1.848
38 × 140 2.851 2.808 2.624 2.694 2.643 2.490 2.568 2.514 2.376
38 × 184 * 3.941 3.790 3.441 3.745 3.600 3.266 3.579 3.441 3.119
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4