How Far Apart Are Joist In A Flat Roof

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.

How far apart are joist in a flat roof. Span calculator for wood joists and rafters also available for the android os. Wane as allowed in bs 4978 2007 a2 2017 is permitted in all sections included in these span tables. This is the distance between joist centres. The drawing is attached its 4 8m x 8m the front height will be around 2 5m and the back 2 2m.

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. Variations in ceiling construction nonparallel ceiling joist designs require additional support construction in the ceiling. Holes drilled at the neutral axis centre line are not to exceed 0 25 of the depth of a joist and are not to be less than three diameters centre to centre apart and are to be located between 0 25 and 0 4 of the span from the support. If the roof is not completely square you can decrease the space between joists but never increase the space.

Joist spacing of 24 inches is allowed for spans between 16 to 20 feet using 2 inch by 10 inch lumber of these three grades. In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. A roof joist is always spaced no more than 16 inches apart from another roof joist. I m told i should use 6 meter 9 x 3 c24 roof joists.

These spacing intervals are measured on center meaning that the measurement is taken from the center of one rafter s horizontal surface to the center of the next rafter. But they do tend to space rafters in one of several industry standard increments typically either 12 16 or 24 inches apart. Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot. Also available for the android os.