Solid timber joist sizes are provided in the bs 8103 3 span tables.
Flat roof joist span c24.
Size of joists mm clear span c16 joist m clear span c24 joist m 47 x 95 47 x 120 47 x 145 47 x 170 47 x 195 47 x 220 1 77 2 40 2 89 3 38 3 87 4 36 2 04 2 75 3 47 4 20 4 93 5 66 floor joists flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.
Live load is weight of furniture wind snow and more.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run.
Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support.
Span calculator for wood joists and rafters also available for the android os.
This demo version is fixed at 1m clear span.
Usually 400 450 or 600mm but any value can be used up to 610mm max.
1 ft 0 3048 m.
This is the distance between joist centres.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
Span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3.
Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.
The full version allows any size.
The lengths and sizes of joists vary depending on the species and quality of the lumber used.
Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size of roof joist 400mm 450mm 600mm 47 x 97 1 84 1 81 1 74 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42 47 x 195 4 41 4 31 3 92 47 x 220 5 04 4 85 4 41 75 x 170 4 50 4 38 3 99.
Where the tables do not apply or where there are concentrated loads floor joists should be designed by an engineer in accordance with technical requirement r5.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
1 enter joist details 1 1 span and joist spacing.
Also available for the android os.
Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no.
Dead load weight of structure and fixed loads 15 lbs ft 2.
For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine.
Rafter and joist span faq.
