Rafter And Purlin Spacing For Metal Roof

For more detailed information on re roofing applications consult fabral tech nical bulletin 721 re roofing with metal.

Rafter and purlin spacing for metal roof.

Purlins are non pressure treated 1 x 4 x 12 lumber that is installed on to the roof in a specific layout pattern and screw pattern. A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel. The width of metal panels will determine the rafter spacing. The wider the roofing panels the greater spacing distance you should put.

Do all roofing projects require purlins. This will provide a solid framework for attaching the metal panels. 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. Wider panels allow for greater spacing between rafters.

The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to. Without a set of blueprints with a pe s seal you have no option but to follow the inspectors gig. Dead load will be the actual weight of the roof steel and the roof purlins. The metal roof purlins spacing must be done correctly within narrow tolerances.

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. I did not know. Rafter spacing is based on the width of the metal roofing panels. There is a chance of damaging roofing sheets if you are failed to do so.

Pole buildings with metal roofs are typically built with metal roofs resting directly on rafters and purlins horizontal members that run between rafters and tie them together. Load tables are available for all fabral panels. He gave me a copy of r802 5 1 3 rafter spans for common lumber species. The inspector asked about the type of wood being used as purlins.

Fyi we run purlins on 3 5 feet on center depending on size of purlin. 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. The table shows one 2 x 8 that will make a 15ft. We do recommend it however.

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. Contact fabral for additional information. Purlin spacing is dependent on profile of the metal and gauge plus snow and wind load plus what the rafters are designed to carry. Purlins should be fastened through the decking and into the rafters.