This calculator is to be used as an estimating tool only.
Flat roof rafter sizes.
This is the distance between rafter centres.
For pitched roofs flat roofs and ceiling joists.
The lengths and sizes of joists vary depending on the species and quality of the lumber used.
The size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof.
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.
They are nailed securely to exterior wall plates and to each other.
Input the rafter span on the flat eave overhang and pitch of the roof.
Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.
Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2.
Usually 400 450 or 600mm but any value can be used up to 610mm max.
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.
Here the number is 1166 66 inches.
This sizing guide for roof rafters will help determine what you need for your small project.
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 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42.
Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak.
Wood beam calculator american wood council website rafter and joist span faq.
Rafter stock size calculator.
For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine.
The rafters in a flat roof serve as ceiling joists for the space below.
Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter.
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.
Automatically calculate suitable rafter sizes enter a specific rafter size 1 3 timber strength.
Surveyors span tables for designing roof rafters.
Click the button to calculate the stock size needed for this job.
Here the number is 941 86 inches.
Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2.
