Flat Roof Joist Sizes Uk

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.

Flat roof joist sizes uk.

Old asbestos roofs are often replaced with flat roofs. For pitched roofs flat roofs and ceiling joists. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. Dead load per square metre in kn m supported by joists.

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. Flat roof with no permanent access and altitude not exceeding 100m 0 75 kn m udl 0 9 kn point load most areas exceeding 100m but not exceeding 200m excluding parts of scotland pennines north east england refer to bs 6399 3 1 kn m udl 0 9 kn point load. If the rafters of a flat roof need to span 18 feet with a deflection limit of their length divided by 360 l 360 they need to be 2 inches by 10 inches or 2 inches by 12 inches depending on the type and grade of timber used. Clear spans for flat roof joists in metres size of roof joists spacing of joists 400mm 450mm 600mm 97 x 47 1 84 1 81 1 74 120 x 47 2 43 2 39 2 27 145 x 47 3 08 3 02 2 87 170 x 47 3 75 3 67 3 42 195.

Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. Sizes of joists needed for flat roof construction. Surveyors span tables for designing roof rafters.

Permissible clear span metres. The joists will normally be placed at 400mm centres but no more than 600mm centres. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. 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 47 x 195 4 41 4 31 3 92 47 x 220 5 04 4 85 4 41 75 x 170 4 50.

So any timber joists that are used need to be strong enough to support this weight. Solid timber joist sizes are provided in the bs 8103 3 span tables.