Surveyors span tables for designing roof rafters.
Flat roof rafter sizes.
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.
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.
This calculator is to be used as an estimating tool only.
This is the distance between rafter centres.
Flat roof joists.
For pitched roofs flat roofs and ceiling joists.
Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2.
Rafter stock size calculator.
Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter.
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.
There are several variables to consider when determining the proper rafter size.
Usually 400 450 or 600mm but any value can be used up to 610mm max.
Automatically calculate suitable rafter sizes enter a specific rafter size 1 3 timber strength.
They are nailed securely to exterior wall plates and to each other.
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.
Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.
Input the rafter span on the flat eave overhang and pitch of the roof.
The lengths and sizes of joists vary depending on the species and quality of the lumber used.
The rafters in a flat roof serve as ceiling joists for the space below.
Click the button to calculate the stock size needed for this job.
This sizing guide for roof rafters will help determine what you need for your small project.
Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak.
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.
Here the number is 941 86 inches.
Here the number is 1166 66 inches.
