Rail and clamp systems are the standard mounting solution for solar PV on pitched metal, tile, and slate roofs. Aluminium rails are fixed to the roof structure at discrete points, either directly to purlins through the cladding or via roof hooks on tiled roofs, and panels are clamped to the rails. Structural engineers check that rail fixing locations align with structural members capable of carrying the transferred loads.
Rail span between fixings must remain within the manufacturer's maximum span to prevent rail bending failure under array dead load and wind uplift. Structural engineers verify fixing spacings against purlin locations identified from drawings or on-site measurement. Where purlin spacing exceeds the maximum rail span, additional fixing points using sub-rails or timber noggins may be required.