Flat Roof Timber Joist Sizes

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.

Flat roof timber joist sizes.

The construction of the flat roof is similar to that of the timber upper floor. Timber and concrete upper floors. 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 floor joists shall be adequate for the spans and loads and be correctly installed.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. 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. Surveyors span tables for designing roof rafters. 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.

They also tell you what the maximum spacing should be between each section or timber member size of joists mm clear span c16 joist m clear span c24 joist m 47 x 95 47 x 120 47 x 145 47 x 170 47 x 195 47 x 220 1 77 2 40 2 89 3 38 3 87 4 36 2 05 2 67 3 22 3 77 4 31 4 85 assumptions at 400mm centers. This is the distance between joist centres. These joists are spaced at a specified distance apart usually 400mm depending on the width or span they are covering and the surface that is to be applied. Solid timber joist sizes are provided in the bs 8103 3 span tables.

Permissible clear span metres. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. For pitched roofs flat roofs and ceiling joists. In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board.