Flat Roof Joist Thickness

There are several variables to consider when determining the proper rafter size.

Flat roof joist thickness.

This sizing guide for roof rafters will help determine what you need for your small project. When installed however the shingles overlap doubling the thickness. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support. The joists will normally be placed at 400mm centres but no more than 600mm centres.

Usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below. Also available for the android os. Cold roofs and warm roofs. As opposed to old built up felt roofing with joins new single ply waterproof membranes are now most commonly used.

Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. There are two types of flat roof. Span calculator for wood joists and rafters also available for the android os. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

Buildingregs4plans flat roof guidance provides information on flat roof deck design and materials including timberboarding plywood oriented strandboard. Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter. Wherever possible joists should span the shortest distance. Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size.

A minimum thickness of 18mm these will be able to span up to 600mm. This is the distance between joist centres. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. Double nailed at each joist.

Laid with the edges of the board corresponding with joists or noggins.