Flat Roof Rafter Sizes

Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter.

Flat roof rafter sizes.

Automatically calculate suitable rafter sizes enter a specific rafter size 1 3 timber strength. 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. The lengths and sizes of joists vary depending on the species and quality of the lumber used. Flat roof joists.

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. 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 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. The rafters in a flat roof serve as ceiling joists for the space below.

Input the rafter span on the flat eave overhang and pitch of the roof. 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. Wood beam calculator american wood council website rafter and joist span faq. They are nailed securely to exterior wall plates and to each other.

Here the number is 1166 66 inches. Click the button to calculate the stock size needed for this job. 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. This calculator is to be used as an estimating tool only.

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. There are several variables to consider when determining the proper rafter size. For pitched roofs flat roofs and ceiling joists. This sizing guide for roof rafters will help determine what you need for your small project.

Surveyors span tables for designing roof rafters. 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. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

This is the distance between rafter centres. Rafter stock size calculator.