Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2 joists for flat roofs.
Flat roof joist sizes uk.
Flat roof joist calculator.
Surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors.
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 04 2 75 3 47 4 20 4 93 5 66 floor joists flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.
Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.
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 size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof.
Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall.
Surveyors span tables for designing roof rafters.
The rafters in a flat roof serve as ceiling joists for the space below.
Subject ceilings and flat roofs timber sizes and construction details 09 issued 01 04 13 rev page 1 of 2 the following tables give details of the allowable spans and spacing for some of the more common timber sizes used in ceiling and flat roof construction.
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 floor joists shall be adequate for the spans and loads and be correctly installed.
Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size of roof joist 400mm 450mm 600mm 47 x 97 1 84 1 81 1 74 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space.
Supporting imposed load.
Enter a specific joist size.
But any value can be used up to 610mm max.
All the figures are based on the normal loading conditions.
For pitched roofs flat roofs and ceiling joists.
Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2.
1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below or.
