Flat Roof Purlin Spacing

Cos of live load dead load x cos of the purlin spacing x purlin span squared 8 x sm section modulus of the member x duration of load 1 15 in areas with snowfall x cr repetitive member factor of 1 15 where members are 24 on center or less fb fiberstress required.

Flat roof purlin spacing.

Standard gage are generally used for roofing. Posts these span tables are designed for a minimum post size of 50 x 50 x 2 5mm up to a maximum height of 3 0m. Further to be considered is the roof framing system as a whole be it truss or rafters wood or steel as the case may be is a factor how purlins are installed at calculated distances apart. Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member.

It is understood that purlins are spaced where laps and splices of roof sheets that vary in sizes. Here is the formula for calculation of a roof purlin. The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft. To determine how far apart to set rafters measure the width of the metal panel and then the width of the first hill and valley of the panel.

Roof live load roof dead load x spacing x span of purlin 2 divided by. 1 psf lb f ft 2 47 88 n m 2. Live load is weight of furniture wind snow and more. Flat roof span tables allow for a maximum roof pitch of 5º.

A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel. Numbers 20 and 22 u s. Dead load weight of structure and fixed loads 15 lbs ft 2. Roof pitch use recommended minimum roof pitches as specified by roof sheet supplier.

In the valleys due to the angle typically produced at the valley and the use of transition flashing it is essential that the purlins are doubled in the valleys that is two purlins side by side on each side of the angle of the valley. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. 8 x section modulus of a 4 2 of 1 3125 x fb fiberstress in bending x 1 15 duration of load x 1 15 cr repetitive member factor as the purlins are spaced 24 o c.

1 ft 0 3048 m. Wider panels allow for greater spacing between rafters. 2 are indicated below.