Flat Roof Joist Span Calculator

Use the span tables below to determine allowable lengths of joists and rafters based on size and standard design loads.

Flat roof joist span calculator.

Span calculator for wood joists and rafters also available for the android os. A completely flat roof is a poor design as water and snow will collect on it eventually leading to your roof collapsing in from the weight of it all. These span tables are the equivalent of other industry standard span tables and are calculated to the same standards. These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. 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. This span table is to the format and methodology given in bs 5268 7 2. To size joists and rafters use the maximum span tables for southern yellow pine.

Click on a span to generate a full calculation you can adjust the exact span. This rafter span calculator is species specific for douglas fir hemlock etc. The smallest pitch of a roof is 0 5 12. More roof calculators roof truss calculator how to cut rafters.

1 enter joist details 1 1 span and joist spacing. Beams of more than one ply must be fastened together with either nails or bolts. The truss is a framework consisting of rafters posts and struts which supports your roof. While every effort has been made to insure the accuracy of the information presented and special effort has been made to assure that the information reflects the state of the art neither the west coast lumber inspection bureau the american wood council nor its members assume any responsibility for any particular design prepared from this online span calculator.

According to the 2012 irc codes any beam joist or header shall never have a bearing of less than 1 1 2. Usually 400 450 or 600mm but any value can be used up to 610mm max. On longer spans the beam may require much more bearing space as indicated by this table. The full version allows any size.

This is the distance between joist centres. These spans were calculated using our flat roof joist calculation engine. This demo version is fixed at 1m clear span. Anything 5 and above we always at least double cripple.

Also available for the android os. This is based upon the span of the rafter horizontal span not total rafter length live and dead loads. Flat roof joist calculator.