These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
C24 flat roof joist span.
This demo version is fixed at 1m clear span.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
This is the distance between joist centres.
Surveyors span tables for designing roof rafters.
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.
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.
The lengths and sizes of joists vary depending on the species and quality of the lumber used.
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.
Usually 400 450 or 600mm but any value can be used up to 610mm max.
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.
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.
Rafter and joist span faq.
Also available for the android os.
Joists under each partition.
For pitched roofs flat roofs and ceiling joists.
The full version allows any size.
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.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
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.
Surveyors and structural engineers utilise data from tables below to help calculate the correct size strength and centres of roof timbers for the required spans and loadings.
