A horizontal roof member that spans between trusses or rafters to directly support the roof covering.
A horizontal structural member in a roof frame that spans between trusses, rafters, or other primary roof framing to support roof decking or cladding. Purlins run parallel to the ridge of the roof and are supported at their ends by the primary structural members. They reduce the span of the roof covering and allow greater spacing of the primary framing.
Purlins are a major line item in pre-engineered metal buildings, so their size, gauge, and spacing drive both the steel takeoff tonnage and the roofing labor estimate. Underestimating purlin spacing or specifying the wrong section can throw off material pricing and trigger costly engineering revisions, making accurate purlin quantification central to a competitive structural bid.
The steel estimator counted 84 cold-formed Z-purlins at 5-foot spacing across the warehouse roof, adding roughly 11 tons to the framing takeoff that drove the structural bid.
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