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Structural

Purlin

In Plain English

A horizontal roof member that spans between trusses or rafters to directly support the roof covering.

Definition

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.

Example

Cold-formed steel Z-purlins at 5-foot spacing span between rigid frames to support the standing-seam metal roof panels.

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