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 2.816 2.816 2.762 2.624 2.682 2.624 2.478
38 × 170 * 3.658 3.596 3.384 3.432 3.361 3.180 3.256 3.180 2.991
38 × 195 * 4.343 4.263 3.876 4.054 3.966 3.645 3.834 3.740 3.459
38 × 220 * 4.987 4.800 4.366 4.681 4.521 4.107 4.415 4.295 3.898
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 2.997 2.997 2.939 2.789 2.852 2.789 2.632
44 × 170 3.890 3.822 3.554 3.645 3.569 3.343 3.455 3.374 3.172
44 × 195 * 4.609 4.472 4.069 4.299 4.204 3.830 4.062 3.963 3.636
44 × 220 * 5.228 5.034 4.583 4.930 4.744 4.314 4.671 4.510 4.097
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 2.427 2.427 2.385 2.274 2.320 2.274 2.155
47 × 145 3.271 3.219 3.081 3.081 3.021 2.866 2.931 2.866 2.703
47 × 170 3.998 3.927 3.633 3.744 3.665 3.418 3.548 3.464 3.245
47 × 195 * 4.732 4.568 4.159 4.412 4.305 3.915 4.168 4.065 3.718
47 × 220 * 5.339 5.142 4.683 5.036 4.847 4.410 4.790 4.609 4.189
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 2.751 2.751 2.700 2.570 2.624 2.570 2.431
63 × 145 3.698 3.636 3.420 3.474 3.404 3.220 3.300 3.225 3.037
63 × 170 4.497 4.388 3.999 4.205 4.114 3.768 3.979 3.884 3.580
63 × 195 5.206 5.017 4.576 4.915 4.734 4.313 4.661 4.505 4.100
63 × 220 5.852 5.642 5.150 5.529 5.327 4.856 5.265 5.070 4.617
72 × 120 3.078 3.032 2.908 2.908 2.854 2.714 2.772 2.714 2.565
72 × 145 3.904 3.837 3.572 3.665 3.590 3.365 3.478 3.399 3.198
72 × 170 4.737 4.577 4.176 4.426 4.320 3.936 4.187 4.086 3.742
72 × 195 5.426 5.231 4.777 5.127 4.940 4.505 4.883 4.703 4.284
72 × 220 6.097 5.881 5.374 5.764 5.556 5.070 5.493 5.292 4.823
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 2.694 2.694 2.643 2.514 2.568 2.514 2.376
38 × 184 * 4.041 3.968 3.659 3.780 3.699 3.441 3.579 3.494 3.266
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4