In steel construction, the term purlin typically refers to roof framing members that span parallel to the building eave, and support the roof decking or sheeting. The purlins are in turn supported by rafters or walls.
Steel purlins are a substitute for conventional wood purlins. They are lightweight, stable in dimension, accurate and simple. In extreme temperature changes, they expand and contract moderately. Steel purlin is typically made of cold-formed material, which is thin enough to get through the screws. Cold-formed steel is rendered in the desired shape by rolling or pressing thin sheets of steel in. To the producer, it is less costly than hot-rolled steel and is, therefore, simpler to deal with. Though cold-formed steel is stronger than hot-formed steel when under strain, it is more likely to crack rather than bend.
Purlins are made of different metals. Some are simple Mild steel having normal strength and some are with zinc coating of different GSM. In harsh weather special coating can be applied over and above zinc coating.
