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A solar panel structural review answers one question before the first bracket goes on a roof: can this structure carry the array, and keep carrying it for the life of the system? In the UK, that check isn’t a courtesy. MCS requires a roof check on every pitched-roof installation, and Building Regulations expect the building to stay structurally sound afterwards. Get it wrong and the repair bill and the callback land on you, not the customer.
What is a solar panel structural review?
A solar panel structural review is a documented check that a building’s structure, and the fixings tying the array to it, can safely resist the extra weight, wind uplift and snow load a PV system introduces. It applies to pitched timber roofs, metal-clad roofs and flat roofs alike. It ends with a record you can hand to a customer, an MCS auditor or building control.
Weight is what most people think of first. LABC’s retrofit guidance puts the fitted mass of current panels at around 20 kg per square metre, which is roughly 0.2 kN/m². That sounds modest until you remember how much of an older roof’s allowance the existing tiles have already used.
Wind is the sneakier problem. Panels are light, so the suction trying to lift them off the roof is often bigger than the load pressing them down. A sound review treats self-weight, snow and uplift as one combined set of load cases, not three separate boxes to tick.
Which UK standards and regulations apply to a solar panel structural review?
Five sets of documents do most of the work. Which ones bite depends on the nation you’re working in and the size of the job.
| Document | What it governs | Why it matters for the review |
| Building Regulations Part A (Approved Document A in England and Wales; Technical Handbook Section 1 in Scotland; Technical Booklet D in Northern Ireland) | Structural safety of the building | The building must stay compliant once the array is on the roof |
| MCS MIS 3002, Issue 6.0 (18 March 2026) | Design and installation of solar PV up to 50 kWp | Sets the roof check, edge-zone and flat roof ballast rules for MCS contractors |
| MCS 012 | Pitched roof installation kits (product certification) | Pitched-roof mounting systems must be certified to it, with a defined route when no suitable kit exists |
| BS EN 1990 and BS EN 1991 (Eurocodes) | Basis of design, self-weight, snow and wind actions | The calculation backbone, used with the UK National Annexes |
| BRE Digest 489 and 495 | Wind loads on roof-based PV; mechanical installation | Source of PV-specific wind pressure coefficients, including for ballasted arrays |
One timing point matters. MCS published MIS 3002 Issue 6.0 on 18 March 2026, and compliance became mandatory for MCS contractors certified against it from 18 June 2026. MCS also publishes MIS 3002:2025 for its redeveloped installer scheme, so confirm which version your certification body audits you against before quoting clause numbers. The references in this guide are to Issue 6.0 and were last checked in October 2026.
The standard also flags a legal wrinkle: where an installation falls under the Building Safety Act, design responsibility passes to the MCS contractor as a duty holder.
What does MIS 3002 require for pitched roofs?
MIS 3002 requires a suitably competent person to check the roof structure on every pitched-roof installation, and it requires a qualified structural engineer whenever the roof is unusual or there’s any doubt (clauses 5.9.4 and 5.9.6). The standard defines a pitched roof as one steeper than 10° and shallower than 70°.
For common roof types, it offers screening methods:
- Timber trussed rafters, Method 1: assume a typical design dead load of 0.785 kN/m², subtract the weight of the existing covering, and treat what’s left as the allowance for the array.
- Trussed rafters, Method 2: assume a typical design imposed load of 0.75 kN/m², subtract the likely snow load for the location from Eurocode 1 (BS EN 1991), and use the remainder. The standard says this method isn’t generally applicable where the pitch exceeds 60°.
- Gable-ended cut roofs (rafters and purlins): calculate the maximum dead load from the TRADA span tables, then subtract the existing covering.
- Cut roofs with hips or valleys, and asymmetric duo-pitched roofs: consult a structural engineer.
Treat these methods as screening tools, not sign-off. They show whether a standard roof has headroom. They can’t show whether someone cut a timber out of it after it was built.
The standard also lists what makes a roof unusual. It’s worth pinning above your desk:
- Construction that isn’t covered by the standard’s Table 1
- Signs of structural distress
- Signs of changes after construction, such as removed or notched timbers, or a heavier replacement covering
- A pitch shallower than 30° to the horizontal
- Features that encourage snow build-up, such as dormers, valleys and parapets
What is the 400 mm edge rule?
Modules shouldn’t be mounted within 400 mm of any edge of a domestic roof unless you take specific measures (clause 5.9.7). Those measures are additional fixings, plus extra roof timbers behind them where needed, to resist the higher uplift in the edge zone. You also need to keep ridge tiles secure, leave rainwater run-off patterns unaffected, make sure snow build-up and shedding can’t injure anyone or damage property, and limit wind noise.
Does an MCS 012 mounting kit replace the structural calculation?
No. A certified kit proves the product. It doesn’t prove the roof. Pitched-roof systems must use products certified to MCS 012 (clause 5.5.2), and the roof check in clause 5.9.4 still applies on top of that.
If no MCS 012 kit suits the job, clause 5.5.5 allows a non-certified mounting system, but only with evidence. You need a structural assessment and wind loading calculation for that specific system, proof that weather-tightness has been maintained, and a record that the components are compatible. You must also show the customer has been told to update their fire risk assessment. These calculations don’t amount to compliance on their own, the standard adds. They must link directly to the design and installation.
How much extra load can a roof take before you need an engineer?
There’s no universal number, but two reference points help. LABC’s retrofit guidance notes that Approved Document A treats added roof loading of 15% or more as a material alteration. An earlier LABC guide treated a single row of panels on a modern trussed rafter roof of up to 9 m span as low-risk, with anything more calling for an engineer’s survey. Check the current LABC edition and your building control body before relying on either.
Now run a real example. Ten 400 W modules cover roughly 20 m². At 20 kg/m² that’s about 400 kg, close to 4 kN, or roughly 0.2 kN/m² across the array. Under Method 1 for trussed rafters, the typical design dead load is 0.785 kN/m². The array alone equals about a quarter of that figure, before you subtract what the existing covering already uses. Whether the remainder is enough depends on the tiles or slates already up there. That’s the calculation the review exists to do, and no rule of thumb replaces it.
Why does wind uplift often matter more than weight?
On most roofs, wind uplift is the governing load, because panels weigh far less than the suction wind creates across an array. Edge and corner zones see the highest pressures, which is why the 400 mm rule exists.
The calculation sits on the Eurocodes: BS EN 1991 for wind and snow actions and BS EN 1990 for load combinations, with BRE Digest 489 supplying PV-specific wind pressures. A quick look at the roof from the loft hatch satisfies none of that.
Members aren’t the only thing that can fail. Check the connections as hard as the timber:
- Tiles and slates: notch or flash them where needed so gaps don’t grow beyond what already existed (clause 5.9.8).
- Metal cladding: check that the sheet thickness suits the bracket and screws and can resist the extra uplift (clause 5.9.9), and that the cladding’s fixings into the main structure can transfer the imposed and uplift loads (clause 5.9.10).
- Edge zones: add fixings and, where needed, timbers behind them.
What changes on flat and ballasted roofs?
MIS 3002 treats any roof under 10° as flat, and the demands go up. Every fixing method needs evidence behind it, and ballasted systems need a structural engineer’s input (clauses 5.9.11 to 5.9.13).
| Fixing method | What MIS 3002 expects |
| Mechanically fixed to a solid deck | A condition survey. Pull-out tests following the Single Ply Roofing Association protocol (S15-19) where pull-out values can’t be reliably calculated. |
| Ballasted | Pressure coefficients from BRE Digest 489 or recognised test data commissioned for solar systems. A coefficient of friction of 0.3 unless the slip layer and membrane combination has been tested. The calculation must declare the friction value used, and anything above 0.3 needs a test report. A qualified structural engineer must be consulted on whether the roof can carry the array and its ballast. |
| Ballasted on gravel or green roofs | A tested friction value, or mechanical restraint against sliding, such as a kerb or tether cables. |
Commercial roofs add another layer. MIS 3002 covers systems up to 50 kWp, so larger arrays sit outside its scope and must satisfy the Building Regulations and structural design standards directly. That’s where surprises live. PBC Today reports that across 575 UK commercial rooftops assessed for solar feasibility, one in three needed structural intervention before panels could go on.
The same article notes that MIS 3002 asks for a suitably competent person and never says that person must be a structural engineer. On a commercial roof, put the engineer on the design team from day one.
How do Building Regulations and building control fit in?
Building Regulations apply to rooftop solar even where planning permission doesn’t. In England and Wales, Part A covers structure and Part P covers electrical safety, and Scotland and Northern Ireland have their own equivalents.
There are two routes. Installers registered with a Competent Persons Scheme approved for the work can self-certify. MIS 3002 allows self-certification in place of building control approval only where the installer is registered with a scheme approved for the scope of work being done (clause 5.1.7). Everyone else notifies building control. Either way, tell the customer who is responsible for the notification, and complete it before handover if it’s yours.
Check your scheme’s scope before you assume structure is covered. Eden District Council has warned that some Competent Persons Scheme providers exclude structure from accreditation, and it asks for a surveyor’s or engineer’s report on the existing roof as part of an application. Councils differ, so ask early.
How do you run a solar panel structural review step by step?
A repeatable process beats heroics on site. Keep the paperwork from every step.
- Gather the facts. Roof type, covering, age, span, timber spacing and any known alterations. Ask for original drawings, but don’t count on getting them.
- Inspect the structure. Look for distress, moisture damage and signs of post-construction modification, from inside the roof space where you can. Photograph everything.
- Classify the roof. Match it against Table 1 in MIS 3002. If it doesn’t fit, or it hits any of the unusual-roof triggers, stop and bring in an engineer.
- Calculate the loads. Add dead load for modules, rails and brackets. Take snow and wind from BS EN 1991 and BRE Digest 489 for the site, and combine them under BS EN 1990.
- Check fixings and edge zones. Confirm bracket spacing and fixing type, apply the 400 mm rule, and verify cladding fixings on metal roofs.
- Record the result. Keep the calculation, assumptions, photographs and the name of whoever signed it off, along with why they were competent to do so. Photographs also help evidence weather-tightness on non-MCS 012 systems.
- Tell the customer what matters. If the roof warranty could be invalidated, you need the customer’s explicit written agreement to proceed. A clause in your standard terms and conditions doesn’t count (clauses 5.9.2 and 5.9.3).
Which structural mistakes should you avoid on solar jobs?
These are judgement calls rather than clauses, but they’re the ones worth auditing first:
- Using the trussed rafter shortcut on a modified roof. The methods assume an unaltered structure. A removed or notched timber breaks the assumption.
- Assuming certified means checked. An MCS 012 kit says nothing about the rafters underneath it.
- Ignoring the edge zone. Layouts that look neat on a proposal drawing often push modules into the first 400 mm.
- Quoting a ballast weight without a friction value. The calculation must declare the coefficient used, and anything above 0.3 needs a test report.
- Treating competent person as anyone on the crew. If you can’t write down why the person who signed off was competent, an auditor won’t accept it either.
When should you bring in a structural engineer?
Use an engineer whenever the standard says so, and more often than it strictly requires. MIS 3002 makes it a requirement for hipped, valleyed and asymmetric roofs, for any unusual roof, for ballasted flat roof systems, and for any case of doubt.
Beyond that, bring one in for commercial roofs and for any non-MCS 012 mounting system where the supplier can’t give you a calculation. MIS 3002 accepts calculations from the manufacturer, a third-party structural engineer or an appropriate software platform, so software output can be enough on paper. An engineer’s signature is what you’ll want if the roof is ever questioned.
How does design support fit into structural reviews?
A structural review is only as good as the layout behind it. One Place Solar, a solar design, engineering and permitting company based in Agra, India, supports installers and EPC contractors across the UK, US, Canada, Australia, New Zealand and the UAE. Its services include permit plan sets, sales proposal design and CAD quality checks. A clear module layout with edge clearances shown lets whoever signs off the roof see exactly what they’re approving.
Solar panel structural review: frequently asked questions
Do I need a structural check for every domestic solar installation in the UK?
For MCS-certified pitched-roof work, yes. MIS 3002 clause 5.9.4 requires a suitably competent person to check the roof can withstand the PV system’s loads, and a structural engineer must be consulted when the roof is unusual or there is any doubt. Building Regulations separately require the building to stay structurally compliant.
How heavy are solar panels per square metre?
LABC’s retrofit guidance puts current panels with their mounting at around 20 kg per square metre, or roughly 0.2 kN/m². Actual weight varies with module size and mounting system, so use the datasheets for the job.
What is the 400 mm rule for solar panels?
MIS 3002 says modules should not be mounted within 400 mm of any edge of a domestic roof unless specific measures are taken. Those measures add fixings, and extra timbers where needed, to resist edge-zone wind uplift, and they cover ridge tiles, run-off, snow and wind noise.
Does an MCS 012 mounting kit replace a structural calculation?
No. MCS 012 certifies the mounting product, not the roof it sits on. The roof check in MIS 3002 clause 5.9.4 still applies. A non-certified system needs a structural assessment and wind loading calculation for that specific mounting system.
Who can carry out a solar panel structural review?
MIS 3002 requires a suitably competent person for the standard roof check, and a qualified structural engineer for unusual roofs and ballasted flat roof systems. The standard doesn’t define who counts as competent, so record why the person who signed off was qualified to do it.
What should you do next?
Pull your last three installs and try to produce, in five minutes, the roof type, the screening method used, the load calculation and the name of the person who signed it off. If any of those is missing, fix the process before the next winter does it for you.
If your team needs design and documentation support on UK solar projects, talk to One Place Solar at oneplacesolar.com.
This guide is general information for installers. It isn’t a substitute for a structural engineer’s assessment of a specific roof.