Flat Roof Timber Joist Sizes

Use recommended minimum roof pitches as specified by roof sheet supplier.

Flat roof timber joist sizes. In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board. Solid timber joist sizes are provided in the bs 8103 3 span tables. 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. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. 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. Dead load per square metre in kn m supported by 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.

Timber and concrete upper floors. 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. 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.

This is the distance between joist centres. The construction of the flat roof is similar to that of the timber upper floor. Wherever possible joists should span the shortest distance. Surveyors span tables for designing roof rafters.

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. For pitched roofs flat roofs and ceiling joists. Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls.

Timber floor joists shall be adequate for the spans and loads and be correctly installed. The sizing and spacing will depend upon the loads imposed on them and the required span. Permissible clear span metres. Spantec has prepared these tables for use by people skilled in the design and specification of the.