Flat Roof Joist Thickness

Span calculator for wood joists and rafters also available for the android os.

Flat roof joist thickness.

This is the distance between joist centres. There are several variables to consider when determining the proper rafter size. A minimum thickness of 18mm these will be able to span up to 600mm. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm.

The joists will normally be placed at 400mm centres but no more than 600mm centres. As opposed to old built up felt roofing with joins new single ply waterproof membranes are now most commonly used. Also available for the android os. Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter.

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. 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. As the single ply roofing association spra points out this type of flat roofing is strong durable completely sealed and usually lasts at least 25 30 years.

Wherever possible joists should span the shortest distance. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. Standard asphalt shingles add very little thickness to the roof because a standard three tab shingle is about 3 16 inch thick. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.

Double nailed at each joist. When installed however the shingles overlap doubling the thickness. Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size. Laid with the edges of the board corresponding with joists or noggins.

Cold roofs and warm roofs.