Flat Roof Timber Joist Sizes

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.

Flat roof timber joist sizes. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. 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. For pitched roofs flat roofs and ceiling joists. 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.

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. Solid timber joist sizes are provided in the bs 8103 3 span tables. In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board. This is the distance between joist centres.

Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Surveyors span tables for designing roof rafters. Timber and concrete upper floors.

Permissible clear span metres. 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. Dead load per square metre in kn m supported by joists. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls.