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Purlins are horizontal beams that are used for structural support in buildings. Most commonly, purlins are major components of roof structures. Roof purlins are supported either by rafters or building walls and the roof deck is laid over the purlins.
Traditional timber framing includes three basic purlin types; the common purlin, the purlin plate and the principal purlin.
Purlins can be made of a number of different materials and are available in a number of different types:
- C Purlins : The shape of these types of purlins is that of a square 'C'. C Purlins are used as Purlins over walls, rafters, floor joists and studs for walls.
- Z purlins : Z purlins resemble the alphabet Z and are also called as Zed Purlins. This shape helps the Purlins to overlap joint and is stronger and studier than the C purlins. As a result, they tend to be used for large-scale structures.
- RHS purlins : For roofs where the support structure is visible once the construction is complete, RHS Purlins may be used (Rectangular Hollow Section). These Purlins are basically hollow, rectangular tubes, with welded ends so there is no steel bar corrosion, damage or seepage.
Purlins are available in variety of materials depending on budget, structural and aesthetic requirements. The most traditional material for purlins is wood. However steel roof purlins and galvanized purlins can offer benefits of durability, cost and structural strength. Cold formed steel and the hot rolled steel processes can be used to create the required shapes from the steel sheets.
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