Flat Roof Purlin Spacing

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

Flat roof purlin spacing.

Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. Numbers 20 and 22 u s. The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft. Roof live load roof dead load x spacing x span of purlin 2 divided by.

Live load is weight of furniture wind snow and more. 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. 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.

A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel. Standard gage are generally used for roofing. 1 psf lb f ft 2 47 88 n m 2. 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.

Wider panels allow for greater spacing between rafters. 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. 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. 1 ft 0 3048 m.

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. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. 2 are indicated below. Roof pitch use recommended minimum roof pitches as specified by roof sheet supplier.

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. 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. Dead load weight of structure and fixed loads 15 lbs ft 2.