Surveyors span tables for designing roof rafters.
Roof rafter size table.
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.
Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal.
Input the rafter span on the flat eave overhang and pitch of the roof.
For pitched roofs flat roofs and ceiling joists.
For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2.
This calculator is to be used as an estimating tool only.
It is always better to have a large rafter rather than be concerned with a sagging roof.