Alectrona
Commercial guideBefore any panels are specified, the roof has to be shown by calculation to carry the array under the worst-case combination of dead, imposed, wind and snow loads. That assessment is what tells you the roof can take the system; a satellite estimate cannot.
These are representative example reviews, not yet-collected customer feedback. They are written to illustrate the kind of feedback Alectrona aims to earn and are shown as design placeholders while we gather and verify reviews from our first commercial clients. Alectrona is the commercial solar trading brand of RVTC LTD.
What set Alectrona apart was the documented design pack. We had quotes from three installers, but only Alectrona handed us a full set of drawings, a single-line diagram and a design referencing BS 7671 and the G99 connection process. The whole thing read like an engineering submission rather than a sales brochure. Our M&E consultant reviewed it and signed it off without a single query. That gave the board the confidence to release the capital.
Other firms priced our roof off a satellite image and a desktop guess. Alectrona flew an in-house drone survey, fully insured and flown by a qualified commercial drone pilot, and built a 3D model of the actual roof. It picked up plant, vents and a parapet line that a flat aerial photo had completely missed, which changed the panel layout. I would rather find that out at design stage than on the day the scaffold goes up. The accuracy of that survey is the reason I trusted everything that followed.
As a finance director I was wary of being oversold a system bigger than we could use. Alectrona modelled the array against our actual half-hourly consumption data rather than an annual total, so it is sized to what we genuinely draw on site during the day. They were honest that exporting surplus is worth far less than self-consumption, and built the design around that. The capital case stacked up because the engineering was honest, not because the numbers were inflated.
We were undecided between buying outright, leasing and a PPA. Alectrona laid out all three side by side with the pros and cons of each against our balance sheet, instead of pushing the one that pays them best. They were clear about where a PPA makes sense and where capex wins, and pointed us at our own accountant for the tax treatment. The survey and design took a little longer than I expected, but the thoroughness was worth the wait. Genuinely consultative.
The install crew were tidy and well run, and worked to a clear CDM 2015 plan with a proper site induction and RAMS. What impressed me most was the handover. We received a full commissioning pack with the IEC 62446-1 test results, certification, O&M documentation and an as-built record for our maintenance team. As the people who have to live with this asset for the next twenty years, having that paperwork in order matters enormously. Nothing was left loose.
I expected the usual hard sell and got the opposite. After surveying our site Alectrona told us one roof section was not worth covering because of shading, and that a smaller, well-sited array was the better investment than filling every square metre. There was no commission-driven upselling and no pressure. For a six-figure capital project, that straight talk is exactly what you want from the people advising you. We will be using them again on our second site.
OrientationThis is orientation, not structural or regulatory advice. The applicable Building Regulations, Eurocodes and the boundary of MCS scope change over time; confirm the current position for your building with a qualified structural engineer and the relevant body before you rely on it.
A structural roof survey answers a single question with engineering certainty: can this roof carry this array, safely, for the array's design life? For a system over 50 kWp the answer comes from a calculation pack rather than a guess. Four load cases are assessed and combined, the load path is traced from the panel clamp down to the foundation, and the roof's remaining life is checked separately from its strength.
This is a plain-English orientation to what that survey covers and why it sits at the front of every commercial project. It explains the load cases, the parts of an industrial roof that usually govern the result, when a chartered structural engineer has to sign it off, and why an on-site assessment beats a desktop estimate. It is a guide, not a structural report; the numbers that matter come only from a calculation done for your specific roof.
A roof under a solar array is carrying more than just the weight of the panels. A structural survey for a commercial system assesses four distinct load cases and then combines them to find the worst case the structure has to survive.
These are quantified using the UK Eurocode actions suite and combined to the basis-of-design standard, BS EN 1990. Wind actions come from BS EN 1991-1-4 and its UK National Annex; snow actions from BS EN 1991-1-3 and its National Annex; the member and connection checks run to the relevant material Eurocode, for example BS EN 1993 for steel. The point a finance director should hold onto is that wind and snow loads are site-specific. They vary by geographic location, altitude, building height and roof shape, so a generic figure from a brochure is not valid for any real roof. BRE Digest 489, the PV-specific wind reference revised in 2014, sits on top of the wind Eurocode for rooftop arrays.
On a warehouse or factory roof the structure rarely fails on gross weight alone. The survey traces the load path from the panel clamp, to the rail, to the fixing, to the sheet or purlin, to the rafter or portal frame, and finally to the column and foundation. The array is only as good as the weakest link in that chain, and on industrial roofs the weak links are usually near the top.
The typical limiting elements are the purlins, the roof sheet and the fixings. The assessment checks purlin span and section capacity, often against the manufacturer's span tables; the capacity of the profiled sheet spanning between purlins; and the pull-out and shear capacity of both existing and new fixings under wind uplift. This is also where weather-tightness can be lost: drilling or fixing into purlins or sheets without a proper assessment can compromise the roof's ability to keep water out, which is a separate failure from a structural one.
As an indication only, a rail-mounted array typically adds in the order of 15 to 25 kg per square metre, while a ballasted flat-roof system can add far more, roughly 50 to 80 kg per square metre, because of the ballast needed to resist uplift. Those are typical ranges, not design values. The real number for your roof comes from the project-specific calculation, and a ballasted flat-roof install is one of the cases that routinely needs a structural engineer because of the extra load it imposes.
Structural capacity and roof condition are two different questions, and a thorough survey answers both. A roof can be strong enough to carry the array and still be the wrong roof to install on, because it does not have enough life left in it.
A solar array has a design life generally taken as 20 to 30 years. Industry guidance from the NFRC is that the roof beneath it should have a comparable remaining lifespan, so the roof does not fail before the asset on top of it does. Installing on an end-of-life roof risks premature roof failure, water ingress beneath the array, the cost of removing and reinstating panels to get at the roof, and disputes over who is responsible for the consequences. The recommended sequence is to address the roof first: where remaining life is inadequate, re-roof or remediate before the array goes up, rather than building over a problem.
This is also why an on-site assessment beats a desktop or satellite estimate. Satellite and aerial imagery cannot reliably show the true condition of existing fixings, corrosion, the state of the sheet or membrane, or near-field obstructions. A drone survey delivers far higher geometric accuracy and can carry thermal imaging to flag moisture ingress, while an actual structural assessment establishes the real load path and remaining capacity. A desktop estimate can produce a plausible-looking layout on a roof that physically cannot take it, or is near the end of its life.
Building Regulations Approved Document A (Structure) always applies to a rooftop array: the structure must be shown by calculation to carry the worst-case combination. For systems up to 50 kWp, which sit inside the domestic-scale MCS scheme, a competent assessor can sign off simple standard roofs and a qualified structural engineer is required for the higher-risk cases.
An engineer, typically chartered through the IStructE or with CEng MICE, should be engaged rather than a general assessor where the roof is non-standard or higher-risk. The cases commonly cited include hipped, valley or asymmetric roofs, dormers and parapets, shallow pitches, ballasted flat-roof installations, older buildings, previous structural alterations, thin metal sheeting or ageing purlins, any visible signs of distress, and high wind-exposure zones.
For a commercial system over 50 kWp this is the key honesty point. That MCS competent-assessor route does not apply: the system sits outside MCS scope, so MCS is not the compliance mechanism at all. The project relies on Building Regulations plus a structural engineer's Eurocode-verified report instead, and that sign-off effectively becomes the expected route. The report concludes with a clear determination: a Pass, a Conditional Pass, or a Fail, supported by the load calculations and a written engineering narrative. A Conditional Pass sets out defined next steps, for example a lightweight non-penetrating mounting system, a reduced array density, or localised strengthening, so you know exactly what the roof will and will not take before you commit.
A structural roof survey is a physical site visit that gathers the evidence the calculation later depends on. The surveyor first establishes safe access under a method statement, because every measurement taken on a fragile or lightweight roof is governed by the work-at-height rules covered in our working at height safety guide. Once on the deck they record the build-up: the sheet or membrane type and profile, the purlin section and spacing, the rafter or portal-frame layout, the fixing pattern, and the span dimensions that drive the member checks. Where the structure is concealed, the original structural drawings are requested and reconciled against what is visible, because a roof rebuilt or re-clad since construction rarely matches its as-designed paperwork.
The visit also captures the condition evidence that no desktop study can produce. The surveyor probes for corrosion at fixings and laps, checks for sheet fatigue and ponding, looks for prior structural alteration, and notes any visible distress such as sagging purlins or cracked welds. On an older industrial roof the asbestos position is read alongside the structure, because the two cannot be separated on this fabric, a point developed in our asbestos on older roofs guide. This is also the stage where a measured roof model is built, whether by hand survey or by drone photogrammetry, so the array layout sits on the true geometry rather than an aerial approximation. The findings feed directly into the wider feasibility study and the usable-area question in our how much roof space guide, so the structural visit pays for itself by killing unviable layouts early.
On a commercial solar project the structural survey is the first design-risk control under the Construction (Design and Management) Regulations 2015. Because a system over 50 kWp sits outside the domestic MCS scheme, CDM 2015 is the framework that governs how design risk is identified and discharged, and the structural assessment is where the principal designer first tests whether the array can be built safely at all. The HSE, which enforces CDM, treats the choice of mounting system and the loading it imposes as a design decision, so the engineer's load model and the principal designer's risk register are read together rather than in sequence. Our CDM 2015 guide sets out how those duties are allocated across the project.
The survey also shapes the rest of the design, beyond the go or no-go decision. A Conditional Pass that calls for a lightweight non-penetrating mounting system, a reduced array density, or localised strengthening becomes a design input that the principal designer carries forward into the installation method and the maintenance access plan. A penetrating fixing into a fragile sheet, for instance, is both a structural action and a weather-tightness and safety risk, so the survey result and the CDM risk control are the same decision viewed from two sides. The resulting engineer's report and load calculations also matter commercially: they are the document an insurer and a future buyer rely on, which is why we treat them as part of the asset record alongside the cover described in our commercial solar insurance guide.
Our own insured pilot flies your roof and captures the real geometry and shading, so the design starts from your building instead of a satellite guess.
Booked to suit your operating hours
We model the array in bankable-grade software, size it around your daytime load, and set out generation, savings and payback across three funding routes.
Modelled, not promised
Designed and installed to BS 7671, commissioned to IEC 62446-1, connected under G99 and run under CDM 2015. Alectrona is typically the Principal Contractor.
Outside MCS, assured by the non-MCS stack
A 12-month defects period backed by an Insurance-Backed Guarantee, then ongoing operations and maintenance so the asset keeps earning for its full working life.
Kept performing, year on year
Last updated June 2026
It checks whether the roof can carry the array under the worst-case combination of four loads: the permanent weight of the panels, rails and fixings; maintenance access; wind uplift, which usually governs on a lightweight roof; and snow. It also traces the load path from the panel clamp down to the foundation, and assesses the remaining life and condition of the roof itself. The loads are quantified using the UK Eurocode actions suite and combined to BS EN 1990.
As an indication only, a rail-mounted array typically adds in the order of 15 to 25 kg per square metre, and a ballasted flat-roof system can add roughly 50 to 80 kg per square metre because of the ballast needed to resist wind uplift. Those are typical ranges, not design figures. The real load for a specific roof comes only from a project-specific calculation, and weight is not the whole story: wind uplift on a lightweight roof can govern the result well before gross weight does.
For a commercial system over 50 kWp, effectively yes. That size sits outside the MCS scheme, so the project relies on Building Regulations plus a structural engineer's Eurocode-verified report rather than MCS competent-person sign-off. An engineer is also the right choice for non-standard or higher-risk roofs: shallow pitches, hipped or valley roofs, parapets, ballasted flat roofs, older buildings, thin sheeting or ageing purlins, and any visible signs of distress. We confirm the route for your specific roof.
Satellite and aerial imagery cannot reliably reveal the true condition of existing fixings, corrosion, the state of the sheet or membrane, or near-field obstructions, and it has limited positional accuracy. A desktop estimate can produce a layout that looks fine on a roof that physically cannot take the array or is near end of life. A drone survey gives far higher geometric accuracy and can carry thermal imaging for moisture, while an on-site structural assessment establishes the real load path and remaining capacity.
The recommended sequence is to address the roof first. A solar array has a design life of roughly 20 to 30 years, and the roof beneath it should have a comparable remaining lifespan so it does not fail first. Installing on an end-of-life roof risks premature roof failure, water ingress under the array, and the cost of removing and reinstating panels to reach the roof. Where remaining life is inadequate, the roof is re-roofed or remediated before the array goes up.
The on-site visit itself is usually a single day for a standard warehouse or factory roof, with the engineer's load calculations and written report following within a couple of weeks, depending on how quickly the original structural drawings can be sourced. It sits near the very front of the project, during the feasibility study stage and before any array is specified, because its result can change the whole design or rule the roof out. Timelines lengthen where structural drawings are missing, the roof needs opening up to confirm hidden members, or remedial works are required first, so confirm the current lead time for your building rather than assuming a fixed figure.
We do not publish a fixed figure, because the cost tracks the roof: its size, height, access and condition, and whether the original structural drawings exist or the roof has to be opened up to confirm hidden members all move the work involved. The survey is set up as part of the early survey stage rather than billed as a standalone line, and a commercial cost is survey-led for that reason, set out in our commercial solar cost guide. We confirm the basis for your building before any work is committed.
A guide can only take you so far. The figure you get is modelled from your own half-hourly load and a system sized from the on-site drone survey. No obligation, and systems this size sit outside the domestic MCS scheme, so the assurance is the engineering stack.