It is always better to have a large rafter rather than be concerned with a sagging roof.
Roof rafter sizes for pitched roof.
Surveyors span tables for designing roof rafters.
Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max are there any brittle finishes e g.
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.
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.
Plasterboard on the underside of the rafter.
Again make sure to consult local codes.
For pitched roofs flat roofs and ceiling joists.
1 1543 x 1 610 1 858m.
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.
The length of rafter per meter of run is 1 1543.
Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak.
All we do now is use a calculator to multiply 1 610 by the measurement in the book.
Here the number is 941 86 inches.
If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center.
Here the number is 1166 66 inches.