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.
Timber roof joist span tables uk.
Surveyors span tables for designing roof rafters.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
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.
Joists are to have minimum end bearing of 40mm.
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For pitched roofs flat roofs and ceiling joists.
Floor joist span tables for surveyors floor construction.
Posi rafters posi rafters combine the lightness of timber and strength of posi strut steel webs to provide a quality roof system that can span further than alternative timber products.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
This is the distance between joist centres.
Posi joists mitek manufactures the steel webs used in posi joists.
Joist spans 2 5m to 4 5m provide strutting at mid span.
These span tables are based on the imposed loads given in bs 5268 7 1 and bs 6399 1 with an imposed uniformly distributed load of 0 25kn m acting together with a concentrated point load of 0 9 kn.
Joist spans over 4 5m provide 2 rows of strutting at third span positions.
Span tables for solid timber joists.
Span tables span tables can be used to determine the size of a timber member of a particular strength class required for a given span.
Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth.
The weight of the timber floor itself consists of the timber joists the plasterboard ceiling underneath it except for suspended timber ground floors the floorboards and the nails or screws used to fix both of the aforementioned coverings.
Proprietary strutting is to be used in accordance with manufacturers recommendations.
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.
Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size.
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.
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