Flat Roof Joist Sizes Uk

These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

Flat roof joist sizes uk.

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. Solid timber joist sizes are provided in the bs 8103 3 span tables. For pitched roofs flat roofs and ceiling joists. 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.

This air is vented at either end of the roof to allow a continuous air flow. 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. Waterproof membrane to prevent water penetrating the structure and interior of the. More common timber sizes used in flat roof construction.

All the figures are based on the normal loading conditions. 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. A flat roof usually consists of the following. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.

Although flat roofs are cheaper to build than pitched roofs they have a shorter life span. 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 with asphalt finish with felt. 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.

Supporting imposed load. 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. A roof is considered to be flat when it is of a slope of 1 5 o to the horizontal.

They are nailed securely to exterior wall plates and to each other. In terms of rules on ventilation bs 5250. All figures are based on. Flat roof joist calculator.

Surveyors span tables for designing roof rafters. Flat roof construction for residential. 2011 control of condensation in buildings is the document to view.