Purlin Spacing For Metal Roofs

Do all roofing projects require purlins.

Purlin spacing for metal roofs.

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. By the standard the most used placement of purlin span for metal roof is five foot intervals. The typical spacing standards for residential and commercial buildings are about 1 to 2 foot.

An engineer will use a load chart in order to determine the spacing between metal purlins. However engineering determines the optimal spacing between the purlins. We do recommend it however. For the lighter material such as lightweight aluminum the common spacing length is 4 inches of clear gap.

This will depend upon the type of panel that is used and the thickness of the steel. Metal roof purlins are installed horizontally under metal roofs. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. If the space between posts is greater than 8 feet then brace is needed to avoid buckling.

Standard gage are generally used for roofing. The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. For 2x6s purlins the posts are spaced in 6 feet distance.

For heavier material such as gage steel the metal roof purlins spacing length could go up to 4 feet. Wider panels allow for greater spacing between rafters. Numbers 20 and 22 u s. Load tables specifying safe loads for different spans are available from metal deck manufacturers.

Screw line spacing for metal roofing over metal purlins. 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. The heavier the expected load is the shorter the distance between the purlins. Purlins are 2 by 4 feet and are installed much like metal roofing.

Once the purlin spacing is determined then the metal roofing panels are typically attached to every line of purlins.