Graphical Construction Glossary >> Roofs and roofing. >> Roof Framing >> purlin

1.) A horizontal roof member, steel or timber, sitting on the principal rafter of a truss or propped off a wall to support the rafters.
2.) A horizontal roof member sitting on the rafters or on a truss or steel member that the roofing material is directly fixed to.

timber under purlins

For most of the history of construction timber or lumber-purlins were as shown in the sketch above. One way or another they supported the common rafters. Also the name carried over when they started to be used on top of the rafters or on top of other members to directly fix the roofing to. More details here.

steel purlins

Looking up at the underside of a roof that is using steel cold rolled Zed-purlins. he steel roof sheeting above has been fixed with self drilling metal thread screws which can be plainly seen where they have penetrated the top flange. More information on the various types of steel-purlins. Note the flat strap cross bracing.

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