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
C24
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 1.865 1.844 1.784 1.784 1.758 1.687 1.717 1.687 1.609
38 × 120 2.552 2.516 2.420 2.420 2.378 2.267 2.313 2.267 2.148
38 × 145 3.264 3.211 3.073 3.073 3.013 2.858 2.923 2.858 2.695
38 × 170 * 3.990 3.920 3.625 3.736 3.657 3.411 3.540 3.456 3.238
38 × 195 * 4.725 4.562 4.151 4.405 4.298 3.907 4.160 4.057 3.709
38 × 220 * 5.334 5.136 4.676 5.030 4.840 4.401 4.782 4.601 4.180
44 × 95 1.996 1.972 1.907 1.907 1.878 1.800 1.833 1.800 1.715
44 × 120 2.723 2.684 2.578 2.578 2.532 2.412 2.462 2.412 2.283
44 × 145 3.474 3.416 3.253 3.266 3.201 3.034 3.104 3.034 2.859
44 × 170 4.237 4.161 3.806 3.963 3.878 3.582 3.752 3.663 3.402
44 × 195 * 4.967 4.784 4.357 4.664 4.510 4.102 4.403 4.288 3.897
44 × 220 * 5.588 5.383 4.906 5.273 5.077 4.621 5.017 4.828 4.390
47 × 95 2.058 2.032 1.964 1.964 1.933 1.852 1.887 1.852 1.764
47 × 120 2.803 2.762 2.652 2.652 2.604 2.479 2.531 2.479 2.346
47 × 145 3.571 3.512 3.324 3.356 3.289 3.116 3.188 3.116 2.935
47 × 170 4.351 4.271 3.889 4.067 3.980 3.662 3.850 3.758 3.478
47 × 195 * 5.072 4.886 4.452 4.784 4.607 4.193 4.515 4.382 3.984
47 × 220 * 5.705 5.497 5.012 5.386 5.186 4.722 5.126 4.933 4.488
63 × 95 2.347 2.316 2.233 2.233 2.196 2.100 2.141 2.100 1.996
63 × 120 3.176 3.127 2.998 2.998 2.941 2.795 2.856 2.795 2.641
63 × 145 4.025 3.955 3.659 3.775 3.697 3.448 3.581 3.498 3.277
63 × 170 4.865 4.689 4.278 4.557 4.426 4.033 4.308 4.204 3.834
63 × 195 5.559 5.359 4.894 5.252 5.061 4.615 5.003 4.818 4.389
63 × 220 6.247 6.025 5.506 5.906 5.693 5.195 5.628 5.422 4.942
72 × 120 3.358 3.305 3.165 3.165 3.105 2.948 3.014 2.948 2.783
72 × 145 4.243 4.169 3.821 3.977 3.894 3.602 3.770 3.682 3.425
72 × 170 5.071 4.889 4.466 4.790 4.618 4.212 4.528 4.397 4.006
72 × 195 5.790 5.586 5.106 5.476 5.278 4.818 5.219 5.028 4.584
72 × 220 6.504 6.277 5.743 6.154 5.935 5.422 5.868 5.656 5.160
ALS/CLS
38 × 89 1.706 1.687 1.636 1.636 1.612 1.550 1.577 1.550 1.482
38 × 114 2.385 2.352 2.266 2.266 2.227 2.126 2.169 2.126 2.017
38 × 140 3.120 3.071 2.942 2.942 2.885 2.739 2.800 2.739 2.585
38 × 184 * 4.401 4.309 3.920 4.110 4.019 3.689 3.887 3.792 3.502
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4