Steel portal frames are the most common structural form for large-span commercial and industrial buildings in the UK. The frame transfers roof loads through the rigid knee and apex joints to the column bases. Portal frame buildings are generally well-suited to rooftop solar because standard steel section sizes allow straightforward load capacity verification.
Structural engineers assess portal frame adequacy for solar PV by obtaining original structural design calculations or commission drawings, then recalculating utilisation under combined load cases including the proposed PV array dead load. Where drawings are unavailable, an on-site structural survey measures column, rafter, and purlin sections for back-calculated capacity checks.