A purlin is a horizontal beam or bar used for structural support in buildings, most commonly in a roof. Purlins are supported either by rafters or the walls of the building. They are most commonly used in metal buildings.
Purlin is important because without it, there’s no frame for the sheeting on the roof to rest on, making purlins critical to the structure of the roof. Purlin is usually made of cold-formed steel that is thin enough to put screws through. Cold-formed steel is made by rolling or pressing thin sheets of steel into the desired shape.
Purlins are manufactured from hot dipped galvanized steel with a coating, in line with other common lightweight steel structural building products. This gives good protection in most exposed internal environments. Run off from, or contact with, materials which are incompatible with zinc should be avoided.To protect the purlin, they also apply a layer of paint outside them. Zinc and paint in combination (synergistic effect) produce a corrosion protection.