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Most modern steel-portal commercial buildings carry solar without strengthening work. What stops projects is rarely weight. It is roof condition. A sheet roof with ten years left cannot host a 25-year array, so a commercial roof survey checks structure, remaining roof life and safe access before anyone prices the job.
That last point catches people out, repeatedly. A finance director sizing up solar is thinking about payback, and the payback runs 25 years. The roof underneath may have twelve. Nobody wants to find that out in year nine, when a leak means stripping an array off to reach the sheets below, then paying to put it back. If you are earlier in the process than this, our full guide to commercial solar panels for UK business covers cost, load profile and grid connection.
How much life has your roof got left?
This is the question that decides the project, and it comes before any load sums.
Your array will carry a 25 to 30 year performance warranty, maybe longer. So the roof has to match it, or something close. Profiled metal roofs can run 40 years in good conditions; cut edge corrosion starts eating the exposed sheet edges long before that, often inside the first decade where the original coating was thin.
| Roof age | What it usually means for solar |
|---|---|
| Under 10 years | Fine. Expect a straightforward survey with no remedial work |
| 10 to 20 years | Workable. Budget for cut edge treatment, lap sealing or new fixings |
| 20 to 30 years | Marginal. Get a roofing report alongside the structural one before committing |
| Over 30 years | Price an overlay or a re-roof into the solar business case, or do the roof first |
There is a version of this that works in your favour. If the roof needs doing anyway, doing it at the same time as the solar means one lot of scaffolding, one lot of access kit, one lot of disruption to the building. Some businesses pull a planned re-roof forward by two or three years, for exactly that reason.
A warning on warranties. Most panel and workmanship cover assumes the roof was sound, structurally and otherwise, when the array went on. Put panels over corroding sheets and a later leak claim can fall into the gap between the roofing warranty and the solar one. Ask who carries that risk, in writing. Our own position is set out in the workmanship warranty.
What a structural survey actually checks
Three loads, then the building that has to take them.
Dead load is the array itself: panels, rails, clamps, cable. On a pitched sheet roof with rail mounting, that comes in around 12 to 18 kg per square metre across the covered area. Light, in structural terms.
Wind uplift is the one that does the damage. Panels behave like a wing, which is the whole problem. An array near a roof edge or corner sees far higher suction than the same array in the middle of the same roof, which is why good designs leave a clear perimeter. Uplift is worked out to BS EN 1991-1-4 and, on flat roofs, BRE Digest 489.
Snow matters because the array changes where snow collects, even where it adds little weight itself.
Then the engineer looks at what carries all that: purlin size and spacing, span, the state of the fixings, whether anyone has already hung ductwork or plant off the frame, and whether the as-built drawings still exist. On an older building they often do not. That means a physical survey rather than a desktop check.
| What adds weight | Typical load (kg/m2) |
|---|---|
| Rail-mounted array on a pitched sheet roof | 12 to 18 |
| Ballasted system on a flat roof, low tilt | 30 to 60 |
| Ballasted system, higher tilt or exposed site | 75 to 100 |
Flat roofs: why ballast changes the sums
Look at that table again. A ballasted flat roof system can weigh four times a rail-mounted one.
That is not over-engineering (though on a quote it reads like it). Nothing bolts through the membrane on a ballasted system, so the only thing holding the array down in a gale is weight. The windier the site and the steeper the tilt, the more concrete goes up there. Which is why a flat roof job that looked simple can come back needing steelwork, while the pitched warehouse next door needs nothing.
There is also a live certification issue worth knowing about. MCS 012, the standard covering solar mounting products, widened its scope in version 3 to take in flat roof systems at pitches of 10 degrees or less. Manufacturers then struggled to get those products certified. In September 2025 MCS confirmed that installers could keep using non-certified flat roof mounting kits under clause 5.5.5 of MIS 3002, until enough certified options exist for them to choose from.
So if you have a flat roof, ask directly: is the mounting system MCS 012 certified, or is it going on under that clause? Neither answer is wrong. But the second puts more weight on the structural and wind calculations your installer produces, and you should see them. Our commercial survey includes those calculations as standard.
Asbestos cement roofs stop more projects than weight does
If your building went up before 2000 and has a profiled fibre-cement roof, assume asbestos until a survey says otherwise.
HSE is blunt about these. Fibre-cement sheets are fragile whatever the profile, they will not take a person's weight, and falls through fragile surfaces account for 22% of all fatal falls from height in construction. Drilling into asbestos cement releases fibres, which rules out fixing an array straight through the sheets.
Two routes work, and both are routine. Strip the roof and replace it, which is licensed work under the Control of Asbestos Regulations 2012 and has to be done by an HSE-licensed contractor to a written plan of work. Or overlay it, fixing the new covering back to the purlins so nothing penetrates the asbestos cement beneath.
Both cost real money. Both add weeks. Neither makes solar impossible, and plenty of farm and barn roofs go this way, with the roof replacement part-funded by the energy saving. It just has to sit in the business case from day one, rather than turn up in week six.
The rule most buyers miss: MCS stops at 50kWp
Here is the thing almost nobody tells commercial buyers, in a quote or anywhere else.
MCS, the scheme behind the certificate you need for Smart Export Guarantee payments, covers solar systems up to 50kWp DC. Above that, your system sits outside MCS scope. Not worse, and not unregulated. But the structural sign-off rules that MCS applies simply do not reach it, and plenty of commercial arrays are well above that line.
Within MCS scope, the rules got tighter this year. MIS 3002 version 6.0 was published on 18 March 2026 and became mandatory on 18 June 2026. Its revised clause 5.5.5 makes installers evidence completed structural and wind loading calculations for the specific mounting system, show how fire performance has been kept, show how weather-tightness has been kept, and confirm the components work with each other.
Above 50kWp, none of that applies by default. What applies instead is Approved Document A and CDM 2015, and the quality of what you get depends entirely on who you hired. Building control guidance commonly treats a roof load increase of 15% or more as a material alteration, which brings Part A into play.
The practical upshot: on a large array, ask your installer to work to the MIS 3002 evidence list anyway. A good one already does, without being asked.
What the survey should cost and what you get
Standalone structural surveys for commercial solar run from roughly £500 to £2,000 per building. Roof count, access and whether the original drawings survive drive most of the variation.
A survey worth paying for gives you:
- a structural appraisal naming the engineer and their qualification
- wind and snow calculations for your postcode, not a generic figure
- a roof condition report covering sheets, fixings, laps and rooflights
- remaining roof life in years, stated plainly
- an access and safety plan, including any fragile surfaces
- a clear yes, no, or yes-with-this-work answer
If what comes back is a one-page PDF saying the roof is suitable, you have bought nothing.
Six things to ask before you sign
- Who is signing off the structure, and what are their qualifications?
- What is the remaining life of my roof in years, and what is that based on?
- Is the mounting system MCS 012 certified, or going on under clause 5.5.5?
- What wind loading figure did you design to, for my postcode?
- If the roof leaks in year eight, who pays to strip and refit the array?
- Is my system above or below 50kWp, and what changes if it is above?
Take those answers into any quote comparison. The gap between a £900 per kW quote and a £1,200 one often sits inside questions three and four. More on that in our breakdown of what a 25-year array costs to put up.
Frequently asked questions
Can my commercial roof take the weight of solar panels?
Usually yes on a modern steel-portal building, which was designed for snow loading well above what an array adds. A rail-mounted array on a pitched sheet roof adds roughly 12 to 18 kg per square metre. Ballasted flat-roof systems weigh considerably more. A structural check confirms it either way.
Do I need a new roof before installing solar panels?
Only if the roof will not outlive the array. Panels carry 25 to 30 year performance warranties, so a roof with under 10 years of life left needs work first. Otherwise you pay twice: once to strip the array, once to refit it. Doing both jobs together saves a second round of scaffolding.
Can solar panels go on an asbestos cement roof?
Not directly. HSE treats fibre-cement sheet as fragile, and drilling into it disturbs asbestos. The two practical routes are licensed removal and re-roofing, or an overlay fixed back to the purlins so nothing penetrates the existing sheets. Both add cost and weeks to the programme.
How long does a commercial roof survey take?
A desktop review takes days where drawings exist. A physical survey is usually half a day on site for a single building, with the report following inside a fortnight. Older buildings with missing paperwork take longer, because the engineer has to measure the frame rather than read it off a drawing.
Does a roof survey replace planning permission and DNO approval?
No. They are separate stages that run alongside each other. Most commercial rooftop solar is permitted development, and the grid side goes through a G99 application your installer submits. Our guide to planning permission and DNO approval covers both.
Written by Luke Kenworthy at OVO Solar & Heating.
Last reviewed 06 October 2026. Standards and HSE guidance referenced were current at that date.
This article covers structural and safety matters in general terms. It is not a substitute for a site-specific engineering appraisal of your building.
Find out what your roof can take
Send us the postcode and the roof age. We will run the desktop structural review and tell you plainly whether your building needs work before solar, what that work is, and roughly what it costs. If the answer is that your roof should be done first, we will say so.
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References
- MCS, "MCS publishes update to MIS 3002", 18 March 2026. https://mcscertified.com/mcs-publishes-update-to-mis-3002/
- MCS, "MIS 3002 V6.0: The Solar PV Installation Standard", published 18 March 2026, mandatory 18 June 2026. https://mcscertified.com/wp-content/uploads/2026/03/MIS-3002_Solar-PV-Systems-V6.0-Final.pdf
- MCS, "Update on investigations into solar mounting certification and flat roof solar PV mounting issues", 1 September 2025. https://mcscertified.com/update-on-investigations-into-solar-mounting-certification-and-flat-roof-solar-pv-mounting-issues/
- Health and Safety Executive, "Fragile surfaces", construction safety topics. https://www.hse.gov.uk/construction/safetytopics/fragile.htm
- Health and Safety Executive, "Health and safety in roof work" (HSG33). https://www.hse.gov.uk/pubns/books/hsg33.htm
- Health and Safety Executive, "Locations of asbestos and taking the right action". https://www.hse.gov.uk/asbestos/location-materials.htm
- GOV.UK, "Structure: Approved Document A". https://www.gov.uk/government/publications/structure-approved-document-a
- Tendring District Council Building Control, "Retrofitting Solar Panels" guidance note, source of the 15% material alteration threshold. https://legacy.tendringdc.gov.uk/sites/default/files/documents/planning/building%20control/Retrofitting%20Solar%20Panels%20PDF%20V2.pdf