Flat Roof Timber Joist Sizes

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.

Flat roof timber joist sizes.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. 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. Wherever possible joists should span the shortest distance. Flat roof span tables allow for a maximum roof pitch of 5º.

Posts these span tables are designed for a minimum post size of 50 x 50 x 2 5mm up to a maximum height of 3 0m. Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600. The construction of the flat roof is similar to that of the timber upper floor. This is the distance between joist centres.

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. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. 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. Use recommended minimum roof pitches as specified by roof sheet supplier.

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. The sizing and spacing will depend upon the loads imposed on them and the required span. The joists will normally be placed at 400mm centres but no more than 600mm centres. Timber and concrete upper floors.

In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board. Permissible clear span metres. Spantec has prepared these tables for use by people skilled in the design and specification of the. 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.

Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. Timber floor joists shall be adequate for the spans and loads and be correctly installed. For pitched roofs flat roofs and ceiling joists. Surveyors span tables for designing roof rafters.