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 2.415 2.420 2.378 2.267 2.313 2.267 2.148
38 × 145 3.264 3.208 2.913 3.073 3.013 2.765 2.923 2.858 2.642
38 × 170 * 3.903 3.754 3.411 3.709 3.567 3.238 3.540 3.411 3.094
38 × 195 * 4.467 4.298 3.907 4.247 4.085 3.709 4.062 3.907 3.545
38 × 220 * 5.030 4.840 4.401 4.783 4.601 4.180 4.577 4.401 3.995
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 2.537 2.578 2.532 2.408 2.462 2.412 2.283
44 × 145 3.474 3.368 3.061 3.266 3.200 2.906 3.104 3.034 2.777
44 × 170 4.094 3.940 3.582 3.893 3.745 3.402 3.726 3.582 3.252
44 × 195 * 4.685 4.510 4.102 4.456 4.288 3.897 4.265 4.102 3.726
44 × 220 * 5.273 5.077 4.621 5.017 4.828 4.390 4.803 4.621 4.198
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 2.594 2.652 2.604 2.463 2.531 2.479 2.346
47 × 145 3.571 3.442 3.129 3.356 3.271 2.971 3.188 3.116 2.840
47 × 170 4.183 4.026 3.662 3.978 3.827 3.478 3.808 3.662 3.325
47 × 195 * 4.786 4.607 4.193 4.553 4.382 3.984 4.359 4.193 3.809
47 × 220 * 5.386 5.186 4.722 5.126 4.933 4.488 4.908 4.722 4.292
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 2.860 2.998 2.941 2.717 2.856 2.795 2.599
63 × 145 3.932 3.786 3.448 3.742 3.602 3.277 3.581 3.448 3.135
63 × 170 4.595 4.426 4.033 4.374 4.212 3.834 4.190 4.033 3.668
63 × 195 5.252 5.061 4.615 5.003 4.818 4.389 4.794 4.615 4.200
63 × 220 5.906 5.693 5.195 5.628 5.422 4.942 5.395 5.195 4.731
72 × 120 3.358 3.282 2.989 3.165 3.105 2.841 3.014 2.948 2.717
72 × 145 4.103 3.952 3.602 3.907 3.761 3.425 3.742 3.602 3.277
72 × 170 4.792 4.618 4.212 4.565 4.397 4.006 4.374 4.212 3.834
72 × 195 5.476 5.278 4.818 5.219 5.028 4.584 5.003 4.818 4.389
72 × 220 6.154 5.935 5.422 5.868 5.656 5.160 5.628 5.422 4.942
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 2.814 2.942 2.885 2.670 2.800 2.739 2.551
38 × 184 * 4.219 4.059 3.689 4.011 3.857 3.502 3.837 3.689 3.346
* Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4