Rafter And Purlin Spacing For Metal Roof

Dead load will be the actual weight of the roof steel and the roof purlins.

Rafter and purlin spacing for metal roof.

I explained the layout of roof trusses and purlins on your building design. Load tables are available for all fabral panels. For sake of discussion we will assume a minimal roof snow load of 20 psf pounds per square foot and a 4 12 roof slope. Without a set of blueprints with a pe s seal you have no option but to follow the inspectors gig.

This will provide a solid framework for attaching the metal panels. Do all roofing projects require purlins. Contact fabral for additional information. I did not know.

The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to. The wider the roofing panels the greater spacing distance you should put. Purlin spacing is dependent on profile of the metal and gauge plus snow and wind load plus what the rafters are designed to carry. The table shows one 2 x 8 that will make a 15ft.

For more detailed information on re roofing applications consult fabral tech nical bulletin 721 re roofing with metal. Purlins should be fastened through the decking and into the rafters. There is a chance of damaging roofing sheets if you are failed to do so. He gave me a copy of r802 5 1 3 rafter spans for common lumber species.

Because this roof design doesn t have the added weight of plywood roof sheathing and metal roofs are generally lighter than asphalt shingle roofs the rafters have much. A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel. Wider panels allow for greater spacing between rafters. The cos of the purlin spacing is because the load on the purlins is vertical and the purlin spacing is with the run of the roof.

The inspector asked about the type of wood being used as purlins. Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch. The metal roof purlins spacing must be done correctly within narrow tolerances. We do recommend it however.

Fyi we run purlins on 3 5 feet on center depending on size of purlin. One of my questions was about snow loads. Rafter spacing is based on the width of the metal roofing panels. The width of metal panels will determine the rafter spacing.