Flat Roof Purlin Spacing

Flat roof span tables allow for a maximum roof pitch of 5º.

Flat roof purlin spacing.

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. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. Non accessible roof and intermediate 1 600 2 400 1 500 2 100 wall cladding type 3 end 1 100 1 600 1 000 1 400 maximum recommended purlin intermediate 0 900 1 500 0 800 1 200 spacing for standard roof end 0 600 1 000 0 550 0 800 see notes below. Standard gage are generally used for roofing.

Roof live load roof dead load x spacing x span of purlin 2 divided by. Wider panels allow for greater spacing between rafters. Here is the formula for calculation of a roof purlin. 2 are indicated below.

Dead load weight of structure and fixed loads 15 lbs ft 2. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. It is understood that purlins are spaced where laps and splices of roof sheets that vary in sizes. 1 psf lb f ft 2 47 88 n m 2.

Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. 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. 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. Roof pitch use recommended minimum roof pitches as specified by roof sheet supplier.

The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft. Doubling up in the valleys refer to the installation manual for the proper on center spacing and be sure that the purlin is attached to the roofing truss. 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. Numbers 20 and 22 u s.

1 ft 0 3048 m. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. 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.