Solar PV on Industrial Roofs: Structural Considerations

Industrial roofs are excellent solar PV platforms — large, flat-ish, owned not let, and unshaded. The structural engineering is rarely a blocker, but skipping the calcs leads to expensive reinforcement later.

Loading considerations

• Dead load: typical PV adds 12–18 kg/m², plus mounting
• Wind uplift: can be substantial at roof edges
• Snow: drift effects at PV array edges
• Maintenance access: point loads from workers and tools

Roof assessment

Before specifying PV, an engineer should:

• Verify original purlin and rafter spans
• Check existing roof condition and tied-in connections
• Calculate residual capacity (subtracting existing dead load)
• Confirm cladding fixing adequacy

Mounting systems

• Through-fix: bolted through cladding to purlin — robust, waterproofing-critical
• Standing-seam clamps: clip onto raised seams — non-penetrating
• Ballasted: weighted frames on flat roof — no penetration but adds substantial dead load

Fire

BR135 and ABI guidance on fire safety has tightened. Key points:

• Combustible underlay or insulation below PV is a risk
• DC isolators must be accessible to firefighters
• Cable management to prevent arc faults
• Spatial separation from other roof elements

Common issues

• Penetration waterproofing failure
• Inadequate purlin capacity in older 1960s/70s sheds
• Lift access requirements during install
• Insurance premium changes

MCFAR structural assesses industrial roofs for PV installations.

Frequently Asked Questions