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 span tables flat roof.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
Surveyors span tables for designing roof rafters.
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.
They also tell you what the maximum.
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.
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.
Flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.
Should refer to trada document span tables for solid timber members in floors ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.