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.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
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.
Usually 400 450 or 600mm but any value can be used up to 610mm max.
These spans were calculated using our flat roof joist calculation engine.
A common choice for flat roofing material is epdm rubber as it is highly durable waterproof and can be made from recycled materials.
This rafter span calculator is species specific for douglas fir hemlock etc.
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.
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.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
This is based upon the span of the rafter horizontal span not total rafter length live and dead loads.
Span calculator for wood joists and rafters also available for the android os.
This is the distance between joist centres.
The full version allows any size.
According to the 2012 irc codes any beam joist or header shall never have a bearing of less than 1 1 2.
Flat roof joist calculator.
Anything 5 and above we always at least double cripple.
Also available for the android os.
On longer spans the beam may require much more bearing space as indicated by this table.
This demo version is fixed at 1m clear span.
Beams of more than one ply must be fastened together with either nails or bolts.
These span tables are the equivalent of other industry standard span tables and are calculated to the same standards.
The smallest pitch of a roof is 0 5 12.
You can also use the wood beam calculator from the american wood council website to determine maximum rafter and joist lengths.
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.
1 enter joist details 1 1 span and joist spacing.
The truss is a framework consisting of rafters posts and struts which supports your roof.
