Purlin Spacing For Steel Roofing

Screw line spacing for metal roofing over metal purlins.

Purlin spacing for steel roofing.

The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. 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. We do recommend it however. Fyi we run purlins on 3 5 feet on center depending on size of purlin.

For 2x4s purlins the posts are spaced in 4 feet distance. The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to. The typical spacing standards for residential and commercial buildings are about 1 to 2 foot. 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.

By the standard the most used placement of purlin span for metal roof is 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. For heavier material such as gage steel the metal roof purlins spacing length could go up to 4 feet.

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. Purlin spacing for metal roofing. Purlin spacing is dependent on profile of the metal and gauge plus snow and wind load plus what the rafters are designed to carry. For the lighter material such as lightweight aluminum the common spacing length is 4 inches of clear gap.

Dead load will be the actual weight of the roof steel and the roof purlins. If the space between posts is greater than 8 feet then brace is needed to avoid buckling. Do all roofing projects require purlins. This will depend upon the type of panel that is used and the thickness of the steel.

Spacing for purlins on a standard load most designs call for purlin placement at five foot intervals. However engineering determines the optimal spacing between the purlins. An engineer will use a load chart in order to determine the spacing between metal purlins.