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.

For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2. If the roof is not completely square you can decrease the space between joists but never increase the space. 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. Wane as allowed in bs 4978 2007 a2 2017 is permitted in all sections included in these span tables.

Im building a summer house shed. In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. The drawing is attached its 4 8m x 8m the front height will be around 2 5m and the back 2 2m. Also available for the android os.

This is the distance between joist centres. Span calculator for wood joists and rafters also available for the android os. I m told i should use 6 meter 9 x 3 c24 roof joists. 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.

A roof joist is always spaced no more than 16 inches apart from another roof joist. 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. 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. For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.