Flat Roof Timber Joist Sizes

Surveyors span tables for designing roof rafters.

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. Permissible clear span metres. 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. 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.

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. 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.

In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board. 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. The construction of the flat roof is similar to that of the timber upper floor. For pitched roofs flat roofs and ceiling joists.

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. Dead load per square metre in kn m supported by joists. 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.