Most of the North East’s commercial solar potential is sitting on profiled steel. Warehouses, factory sheds, distribution units, agricultural buildings — the region’s working roof stock is overwhelmingly sheet metal, and that is good news, because a sound trapezoidal or standing-seam roof is about the best host a solar array can have. This is the roof type we prefer to work on, so here is what actually matters when you put panels on one: the mounting, the pitch, the weight, the sequencing — and the one sheet roof we refuse to drill.
Why the sheet roof is the ideal host
Three reasons, all structural. First, span: a steel portal-frame building offers hundreds or thousands of square metres of continuous, unshaded roof, which is where commercial solar economics come from — plan around 5–6 m² per kWp on a pitched sheet roof once rooflights and access strips are worked around.
Second, weight: profiled steel plus purlins is a light, predictable structure, and a panel array adds typically 12–20 kg per square metre — modest, but never assumed; the structural check on purlins and fixings is part of every survey we do.
Third, speed: no tiles to lift, no wet trade, no slates to match. A clamp-mounted array on sound sheet goes on in days, with the building working underneath it.
A sizing note while we are here, because brochures blur it: kWp is just panel count × panel wattage ÷ 1,000. A 100 kWp array is around 210–220 modern commercial modules at today’s typical 450–480 W ratings — which is why the roof area, not the brochure, decides what your building can carry.
Mounting, profile by profile
Trapezoidal / box-profile sheet. The bulk of the region’s industrial roof stock. Purpose-made brackets fix through the crown of the profile — the ridge line of each corrugation, where water never sits — with sealed fixings driven into the purlins beneath, and mounting rails carrying the panels above. Quick, proven, and weathertight when the bracket matches the profile, which is a check, not a hope.
Standing seam. The best mounting scenario there is: clamps grip the raised seam itself, so on most standing-seam profiles there is no penetration of the roof skin at all. The discipline here is clamp choice and torque — a seam clamp is specified to the exact seam profile, not bought generically.
Composite / sandwich panels. Workable, with care: fixings must land in structure, not just the outer skin, and the panel manufacturer’s guidance on point loads and thermal movement gets read before anyone drills. This is where an installer’s engineering habits show.
Asbestos cement. The exception, stated plainly: we do not drill or fix into asbestos sheet under any circumstances. If your shed roof is asbestos cement — common on buildings from before the mid-1980s — the honest options are stripping and re-sheeting first, using a different roof on the site, or a ground-mounted array. Anyone offering to fix panels straight through asbestos cement is offering you a problem.
The shallow-pitch penalty, measured rather than guessed
Sheet roofs are shallow — typically pitched far below the textbook-optimal angle — and most installers wave at that with “orientation affects output”. We modelled it instead, running the European Commission’s PVGIS yield model for Durham: about 937 kWh per kWp a year at an ideal 35° south-facing pitch, 841 at the 10° pitch a typical sheet roof actually has, and 770 facing east or west at the same shallow pitch.
So the shallow-pitch penalty is real, and it is about 10% — priced into our quotes from the start rather than discovered at handover. Two useful things follow. A south-facing shallow sheet roof in Durham still out-yields a badly oriented roof anywhere in the country, so orientation beats latitude. And an east–west duo-pitch shed, written off by rule-of-thumb installers, often models perfectly well: the yield per face is lower, but generation spreads across the working day instead of spiking at noon — a better match for a building that draws power from eight until six, and self-consumption is where the money is.
Wind, layout and the survey that earns its fee
Weight is rarely the constraint on a steel roof; wind is the one that gets skipped. Uplift calculations set the fixing density — more fixings at edges and corners where wind load concentrates — and the layout keeps arrays clear of the perimeter zones, the rooflights and the access routes a maintenance team will actually need. Cut-edge corrosion on older sheet, the condition of fixings, UV-brittle rooflights that cannot be walked: all of it is survey material, and all of it is cheaper to find before the scaffold goes up. This is engineering first and product second, which suits us — we are an electrical contractor of 30+ years’ standing, and the array is wiring and structure long before it is a brochure.
What it costs on this kind of roof
A clamp-mounted array on sound sheet metal is the cheap end of commercial solar: budget within the 2026 planning band of £700–£1,100 per kWp installed, with sheet-roof projects tending toward the friendlier half of it because the mounting is fast and the access is simple. Scale helps too — government cost data shows the median installed cost per kW falling by roughly a third between the smallest systems and the 10–50 kW band, and the curve keeps falling from there.
What moves an individual quote is rarely the panels: it is roof condition, structural work, access and the grid connection — the G99 application to Northern Powergrid that almost every commercial system needs, which we submit first because it usually takes longer than the installation.
Planning, for completeness: most rooftop solar on non-domestic buildings in England is permitted development — the old 1 MW cap was removed in November 2023 — with systems above 50 kW involving a prior-approval application covering design and glare. Sheet-roof arrays sit comfortably inside those rules on almost every industrial building we see.
The short version
If your building has a sound trapezoidal or standing-seam roof, you own one of the best solar sites in the North East and the questions are only engineering ones: purlins, fixings, pitch, remaining roof life, grid headroom. If the roof is tired or asbestos, sequence the roof first — and if it is a farm shed, the agricultural version of this article covers the load-profile side. Either way, put your roof through the calculator or send us the building and you will get a straight answer, including “re-roof first” when that is the truth.