Flat Roof Rafter Span Calculator

Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.

Flat roof rafter span calculator.

Input the rafter span on the flat eave overhang and pitch of the roof. These spans were calculated using our flat roof joist calculation engine. Area span on the flat please enter area span on the flat in foot. These span tables are the equivalent of other industry standard span tables and are calculated to the same standards.

Surveyors span tables for designing roof rafters. Rafter run outer wall this should be measured starting from the center of the roof span and then extending to the very edge of the exterior wall. Here the number is 1166 66 inches. Here the number is 941 86 inches.

Use the span tables below to determine allowable lengths of joists and rafters based on size and standard design loads. 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. For a gothic style the rafters must equal the span 60 while an elizabethan style requires the rafters to be longer than the span. This calculator is to be used as an estimating tool only.

This span table is to the format and methodology given in bs 5268 7 2. Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak. In snowy areas your roof should be at least 10 12 40 to allow snow to shed while the safest roof pitch in very windy areas is between 4 12 6 12 18 5 26 5. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run.

Also available for the android os. Click on a span to generate a full calculation you can adjust the exact span. 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. You can also use the wood beam calculator from the american wood council website to determine maximum rafter and joist lengths.

Span calculator for wood joists and rafters also available for the android os. Should refer to trada document span tables for solid timber members in floors ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.