Flat Roof Joist Span Calculator

Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope.

Flat roof joist span calculator.

Also available for the android os. Span calculator for wood joists and rafters also available for the android os. To size joists and rafters use the maximum span tables for southern yellow pine. This rafter span calculator is species specific for douglas fir hemlock etc.

1 enter joist details 1 1 span and joist spacing. Flat roof joist calculator. This span table is to the format and methodology given in bs 5268 7 2. 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.

The truss is a framework consisting of rafters posts and struts which supports your roof. The full version allows any size. For pitched roofs flat roofs and ceiling joists 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. This is based upon the span of the rafter horizontal span not total rafter length live and dead loads.

Find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres. The important point to keep in mind when you use your truss calculator is that every truss calculation is completely unique and is based on the size of your roof and its specific dimensions. This demo version is fixed at 1m clear span. This is the distance between joist centres.

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. More roof calculators roof truss calculator how to cut rafters. Usually 400 450 or 600mm but any value can be used up to 610mm max. Click on a span to generate a full calculation you can adjust the exact span.