Commercial Roof Structural Assessment for Solar PV

Why structural assessment matters

Commercial solar PV adds 12-14 kg/m² of imposed load to the roof. Most modern steel-portal commercial buildings (post-1985) are designed for at least 15 kg/m² imposed load, with significant safety margin. Older buildings, unusual roof structures, and buildings with previous structural alterations may not have the same margin — and a failed structural assessment is a project-killer.

What KMM's structural assessment covers

1. Drone capture of roof condition — visible damage, ponding, rust, membrane wear
2. Roof drawings or as-built information from the building owner
3. Existing structural calculations — original design margin against imposed load
4. Additional dead load from solar system — typically 12-14 kg/m² distributed
5. Wind uplift assessment — solar arrays catch wind; the install method must resist uplift
6. Connection point analysis — where the rails attach to the roof, what they bear into (purlins, trusses, parapet)
7. Independent structural engineer sign-off if margin is close, or if the building is unusual

When an independent engineer is required

• Buildings older than 1985 with no current structural drawings
• Buildings with non-standard roof structures (timber trusses, concrete slab, unusual spans)
• Buildings with previous structural alterations (extensions, mezzanines, roof penetrations)
• Listed buildings (always — Listed Building Consent process requires it)
• Buildings where the original imposed-load design margin is below 30 kg/m²
• Projects above 250kWp where the cumulative loading matters

Cost in 2026

What if my roof fails the structural assessment?

• Ground-mount alternative — if you have available adjacent land, ground-mount sidesteps the roof issue entirely
• Lighter array — frameless / lighter panels can reduce load by 15-20%, sometimes enough to clear the margin
• Smaller system — install on only part of the roof where the structure is sound
• Reinforcement — economically viable only on a few projects; usually kills the case
• Wait for re-roof — if the building is due a re-roof in 5-10 years, plan solar for that window with reinforcement designed in

How KMM approaches it

Every KMM commercial proposal starts with a drone-led roof capture, which gives us enough information to run a desktop structural assessment for typical post-1995 commercial buildings. If the desktop assessment flags any concerns, we commission an independent structural engineer and pay for the report as part of our project fee. We do not pass that cost to the customer for projects we expect to deliver.

FAQs