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 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.