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 timber sizes and spans.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
In any other situation you should refer to trada document span tables for solid timber members in floors.
Surveyors span tables for designing roof rafters.
Live load is weight of furniture wind snow and more.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches.
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.
2 are indicated 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.
For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
1 ft 0 3048 m.
Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot.
For pitched roofs flat roofs and ceiling 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.
1 psf lb f ft 2 47 88 n m 2.
All figures are based on normal loading conditions found in domestic construction.
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.
All the figures are based on the normal loading conditions.
Spans in feet to out of bearing spans in feet to out of bearing 5 12 38 47 57 39 51 59 42 56 63 45 54 68.
Roof truss span chart.
The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in flat roof construction.
