The C Z Purlins when using a screed on a certain slope, it is necessary to consider the angle of the purlin in combination with the knowledge of the rake, and the slope is large and the Z purlin can be used. A purlin is a horizontal beam or bar used for structural support. It is mainly below the roof and supported by the buildings walls. C Z Purlins are designed to form the walls and floor joists of a building shell structure.