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 1.168 1.160 1.136 1.136 1.124 1.092 1.106 1.092 1.055
38 × 120 1.758 1.743 1.693 1.693 1.670 1.608 1.634 1.608 1.536
38 × 145 2.309 2.289 2.235 2.235 2.210 2.142 2.171 2.142 2.052
38 × 170 * 2.887 2.859 2.781 2.781 2.745 2.649 2.690 2.649 2.540
38 × 195 * 3.488 3.450 3.305 3.344 3.296 3.169 3.223 3.169 3.027
38 × 220 * 4.106 4.056 3.725 3.920 3.859 3.576 3.766 3.697 3.446
44 × 95 1.342 1.331 1.300 1.300 1.286 1.246 1.263 1.246 1.199
44 × 120 1.895 1.881 1.843 1.843 1.825 1.775 1.797 1.775 1.717
44 × 145 2.481 2.459 2.399 2.399 2.371 2.295 2.328 2.295 2.209
44 × 170 3.096 3.065 2.978 2.978 2.939 2.833 2.878 2.833 2.713
44 × 195 * 3.733 3.690 3.475 3.574 3.522 3.337 3.441 3.382 3.218
44 × 220 * 4.386 4.314 3.916 4.182 4.115 3.762 4.013 3.939 3.628
47 × 95 1.395 1.387 1.364 1.364 1.354 1.320 1.336 1.320 1.269
47 × 120 1.959 1.944 1.904 1.904 1.885 1.833 1.855 1.833 1.772
47 × 145 2.562 2.539 2.476 2.476 2.446 2.367 2.401 2.367 2.276
47 × 170 3.194 3.161 3.070 3.070 3.029 2.918 2.965 2.918 2.794
47 × 195 * 3.847 3.802 3.554 3.681 3.626 3.414 3.542 3.481 3.292
47 × 220 * 4.516 4.410 4.003 4.303 4.234 3.847 4.128 4.051 3.711
63 × 95 1.620 1.610 1.581 1.581 1.568 1.530 1.546 1.530 1.486
63 × 120 2.262 2.244 2.193 2.193 2.170 2.105 2.133 2.105 2.031
63 × 145 2.943 2.915 2.837 2.837 2.801 2.704 2.745 2.704 2.595
63 × 170 3.653 3.612 3.424 3.502 3.452 3.291 3.376 3.319 3.172
63 × 195 4.381 4.313 3.922 4.182 4.117 3.770 4.017 3.945 3.639
63 × 220 5.045 4.856 4.418 4.856 4.673 4.248 4.666 4.513 4.100
72 × 120 2.411 2.391 2.335 2.335 2.309 2.239 2.269 2.239 2.157
72 × 145 3.130 3.099 3.013 3.013 2.974 2.869 2.914 2.869 2.751
72 × 170 3.876 3.832 3.580 3.712 3.658 3.443 3.575 3.515 3.323
72 × 195 4.640 4.505 4.100 4.425 4.335 3.942 4.247 4.169 3.806
72 × 220 5.265 5.070 4.617 5.070 4.881 4.441 4.900 4.716 4.288
ALS/CLS
38 × 89 1.039 1.033 1.012 1.012 1.004 0.978 0.989 0.978 0.946
38 × 114 1.611 1.596 1.553 1.553 1.533 1.479 1.502 1.479 1.417
38 × 140 2.196 2.178 2.128 2.128 2.105 2.041 2.069 2.041 1.947
38 × 184 * 3.222 3.188 3.095 3.095 3.052 2.939 2.987 2.939 2.812
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4