Z and C Purlins: The Backbone of PEB Secondary Framing In a Pre-Engineered Building (PEB), the primary steel frame provides the main structural system, while secondary framing members support the building envelope and help transfer loads to the main structure. Among these secondary members, Z and C purlins play a critical role in supporting roof and wall systems. Although they may not be as visually prominent as the main frames, they are an essential part of an efficient and well-engineered PEB system. What