Purlin Spacing For Steel Roofing

An engineer will use a load chart in order to determine the spacing between metal purlins.

Purlin spacing for steel roofing.

For the lighter material such as lightweight aluminum the common spacing length is 4 inches of clear gap. Purlin spacing is dependent on profile of the metal and gauge plus snow and wind load plus what the rafters are designed to carry. Without a set of blueprints with a pe s seal you have no option but to follow the inspectors gig. The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to.

Do all roofing projects require purlins. Screw line spacing for metal roofing over metal purlins. For 2x4s purlins the posts are spaced in 4 feet distance. By the standard the most used placement of purlin span for metal roof is five foot intervals.

Dead load will be the actual weight of the roof steel and the roof purlins. This will depend upon the type of panel that is used and the thickness of the steel. 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. Purlin spacing for metal roofing.

For 2x6s purlins the posts are spaced in 6 feet distance. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. Spacing for purlins on a standard load most designs call for purlin placement at five foot intervals. The heavier the expected load is the shorter the distance between the purlins.

Once the purlin spacing is determined then the metal roofing panels are typically attached to every line of purlins. If the space between posts is greater than 8 feet then brace is needed to avoid buckling. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. However engineering determines the optimal spacing between the purlins.

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. The typical spacing standards for residential and commercial buildings are about 1 to 2 foot. We do recommend it however.