Span tables allow users to choose an appropriate size and stress grade to achieve spanning needs.

Timber flat roof section. Stress grades and timber sizes combine to determine the spanning ability of load carrying members. The evolution of the flat roof christian schittich. In the majority of cases the covering will be plywood or osb timber which is more commonly called stirling board. Flat roofs of this type are usually finished in steel roof sheet and fall towards a special type of gutter called a box gutter.

Once the section has been set out the length of the common rafter can be determined by drawing the rise and the span as a right angle joined together by the hypotenuse which will determine the slope of the roof. Modern timber roofs are mostly framed with pairs of common rafters or prefabricated wooden trusses fastened together with truss connector plates timber framed and historic buildings may be framed with principal rafters or timber roof trusses roofs are also designated as warm or cold roof depending on how they are designed and built with regard to thermal building insulation and ventilation. The roof section can be set out full size or to scale. Additional construction details drawings.

For additional stability you can also use steel joists that are built into one or both of the walls. Span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3. Having a manual for warm flat roof construction with details and a summary of rules to follow helps. For simple construction such as domestic construction this can be determined from span table supplements in as1684 2 and as1684 3.

When timbers are used in flat roofing they obviously need to be waterproofed so boards are normally laid across the joists and then a felt or rubber is used to cover the boards to make them waterproof. But this type of roof is seldom as attractive as the pitched form as it can result in a blocky stunted appearance. Rainer barthel 1 loadbearing structure matthias beckh mark. The supporting structure and the covering.

The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. For homebuilders a timber frame for a flat roof is usually the cheapest option and the easiest to build.

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