Z Purlins: Shaped like the letter "Z" when viewed from the side, Z purlins are commonly used and are efficient for supporting vertical loads. They have flanges that form the shape of the letter "Z" and are attached to the top of the rafters or trusses.
C Purlins: C purlins have a shape similar to the letter "C" and are attached to the top of the rafters or trusses. They are commonly used in roof construction and are effective for supporting loads in a horizontal direction.
Boxed or "Sleeved" Purlins: In some applications, purlins may be boxed or sleeved to provide additional strength and stiffness. This involves enclosing the open side of the C or Z shape with an additional piece of material.