Purlins are among the most critical structural elements for rooftop solar PV installations. The PV racking system typically transfers array dead load, snow load, and wind uplift directly into the purlins via rail clamps or direct fixing. Purlin capacity, determined by section properties, span, and fixing configuration, is the governing structural check for the majority of commercial portal frame roofs.
Cold-formed steel Z and C purlins are the most common type on UK commercial portal frame buildings. Section capacities are published by manufacturers and are used alongside actual purlin spacing and span, as measured during an on-site structural survey, to verify that proposed PV loads remain within allowable limits under MIS 3002 V6.0 requirements.