Wednesday’s Word Of The Week: Purlin

*Wednesday’s Word Of The Week is a new feature on Unalam’s Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.

Purlins run between arches to the left and right of the ridge beam.

Purlin: A beam is any solid structural member, loaded along its length, and spanning between supports. Because there are so many ways for beams to be oriented and installed, various terms are used to describe specific types of beams. One term, commonly used in glulam construction, is purlin.

Purlins between trusses.

A purlin is a beam used on a sloped roof that runs parallel to the eave and ridge (across the slope.) Purlins can be installed plumb (with vertical sides and an angled “eave” cut on top) or square to the roof. The most efficient glulam purlins are typically plumb with a height up to 6 times the width. Wider sizes are required when installed square to the roof, particularly steep roofs. Purlins are produced from “bending” layups (for example Southern Yellow Pine combination 24F-V3.)