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.
Why portal frame buildings suit rooftop solar
The standardised steel sections used in portal frame construction make load-capacity verification relatively straightforward, and the large clear-span roofs typical of portal frame warehouses and industrial units give commercial solar PV the uninterrupted area it needs. This is why the majority of UK commercial rooftop solar sits on portal frame structures.
The common portal frame constraint
The limiting factor is rarely the main frame; it is more often the secondary steelwork. Purlin capacity, fixing pull-out and the existing roof condition govern whether a given portal frame roof can carry the proposed array without strengthening, and these are checked against the Eurocode load combinations before installation.