Flat Roof Timber Sizes

There are several variables to consider when determining the proper rafter size.

Flat roof timber sizes. This sizing guide for roof rafters will help determine what you need for your small project. Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter. Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak. Automatically calculate suitable rafter sizes enter a specific rafter size.

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 to be covered these span tables do not apply to timber which is fully exposed to the elements. Supporting imposed load. 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.

Here the number is 941 86 inches. For pitched roofs flat roofs and ceiling joists. Flat roof joists. 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.

Calculations to bs 5268 2. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. 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. 2002 bs 5268 7 5.

Structural calculations for timber joists timber beams glulam beams flitch beams using the latest design codes. Flat roofs timber sizes and construction. Surveyors span tables for designing roof rafters. 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 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.