Flat Roof Joist Sizes Uk

All the figures are based on the normal loading conditions.

Flat roof joist sizes uk.

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. Flat roof construction for residential. Supporting imposed load. Surveyors span tables for designing roof rafters.

A roof is considered to be flat when it is of a slope of 1 5 o to the horizontal. 2011 control of condensation in buildings is the document to view. For pitched roofs flat roofs and ceiling joists. This air is vented at either end of the roof to allow a continuous air flow.

Waterproof membrane to prevent water penetrating the structure and interior of the. Although flat roofs are cheaper to build than pitched roofs they have a shorter life span. Enter a specific joist size 2 loadings. Solid timber joist sizes are provided in the bs 8103 3 span tables.

They are nailed securely to exterior wall plates and to each other. More common timber sizes used in flat roof construction. 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. These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

A flat roof usually consists of the following. 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. 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. Put simply a warm flat roof has insulation of some kind packed into every available void and a cold flat roof allows air to circulate between the joists.

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. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. Flat roof with asphalt finish with felt. In terms of rules on ventilation bs 5250.

The rafters in a flat roof serve as ceiling joists for the space below. All figures are based on. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support.