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 1.389 1.381 1.358 1.358 1.348 1.318 1.331 1.318 1.282
38 × 120 1.951 1.937 1.896 1.896 1.878 1.826 1.848 1.826 1.765
38 × 145 2.553 2.530 2.467 2.467 2.438 2.359 2.392 2.359 2.268
38 × 170 * 3.184 3.151 3.061 3.061 3.019 2.909 2.956 2.909 2.785
38 × 195 * 3.837 3.792 3.545 3.671 3.616 3.405 3.532 3.471 3.283
38 × 220 * 4.506 4.401 3.995 4.293 4.224 3.837 4.118 4.041 3.701
44 × 95 1.498 1.489 1.464 1.464 1.452 1.418 1.433 1.418 1.378
44 × 120 2.099 2.083 2.037 2.037 2.016 1.958 1.983 1.958 1.891
44 × 145 2.739 2.714 2.643 2.643 2.611 2.523 2.561 2.523 2.424
44 × 170 3.409 3.372 3.252 3.272 3.227 3.105 3.157 3.105 2.970
44 × 195 * 4.099 4.050 3.726 3.917 3.857 3.580 3.765 3.698 3.453
44 × 220 * 4.803 4.621 4.198 4.573 4.444 4.034 4.382 4.290 3.892
47 × 95 1.550 1.540 1.513 1.513 1.501 1.465 1.481 1.465 1.423
47 × 120 2.168 2.151 2.103 2.103 2.081 2.020 2.045 2.020 1.950
47 × 145 2.826 2.799 2.726 2.726 2.692 2.600 2.639 2.600 2.497
47 × 170 3.513 3.475 3.325 3.370 3.323 3.195 3.250 3.197 3.056
47 × 195 * 4.221 4.170 3.809 4.030 3.969 3.661 3.873 3.804 3.532
47 × 220 * 4.908 4.722 4.292 4.702 4.542 4.125 4.505 4.386 3.980
63 × 95 1.794 1.782 1.748 1.748 1.732 1.688 1.707 1.688 1.636
63 × 120 2.496 2.474 2.415 2.415 2.388 2.313 2.345 2.313 2.228
63 × 145 3.237 3.204 3.113 3.113 3.072 2.962 3.009 2.962 2.838
63 × 170 4.005 3.959 3.668 3.833 3.776 3.527 3.689 3.625 3.405
63 × 195 4.792 4.615 4.200 4.565 4.442 4.040 4.380 4.291 3.900
63 × 220 5.395 5.195 4.731 5.195 5.001 4.550 5.021 4.832 4.394
72 × 120 2.657 2.633 2.568 2.568 2.538 2.456 2.491 2.456 2.363
72 × 145 3.438 3.401 3.277 3.303 3.258 3.138 3.189 3.138 3.004
72 × 170 4.244 4.194 3.834 4.057 3.996 3.688 3.902 3.833 3.561
72 × 195 5.003 4.818 4.389 4.818 4.639 4.222 4.624 4.483 4.078
72 × 220 5.628 5.422 4.942 5.422 5.221 4.755 5.242 5.047 4.593
ALS/CLS
38 × 89 1.261 1.254 1.235 1.235 1.226 1.201 1.212 1.201 1.170
38 × 114 1.812 1.800 1.764 1.764 1.747 1.701 1.721 1.701 1.647
38 × 140 2.430 2.409 2.351 2.351 2.324 2.250 2.282 2.250 2.166
38 × 184 * 3.547 3.508 3.346 3.401 3.352 3.214 3.277 3.222 3.078
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4