Solar Carport Frame and Structure: Steel and Wind Loading

Why the frame is the real engineering challenge

A solar carport is, structurally, a free-standing steel canopy that happens to carry PV modules. Unlike a rooftop array, which borrows an existing building's structure, the carport frame has to do everything itself: hold the panels at the correct tilt, resist wind trying to lift it off its foundations, carry snow without sagging, and survive vehicle proximity for decades. Put simply: the modules are the cheap, replaceable part; the steelwork is the 30-year commitment. This is exactly where thin product-catalogue pages fall down, listing panel wattage but never the column spans, foundation options or load cases a UK building-control officer will actually ask about. On a typical 200-bay scheme (around 300 kWp at roughly 1.5 kWp per bay) the structure and groundworks are the dominant share of the roughly £290k-£390k turnkey cost, so understanding the frame is understanding where your money goes and why a well-sited carport typically pays back in around 4-6 years, or 3-4 after AIA full-expensing.

Steel frame: galvanised S355 and EN 1090 fabrication

For UK commercial carports we specify structural steel to grade S355 for primary columns and beams, a higher-strength steel than the older S275, which lets us achieve longer clear spans with slimmer sections, important when you are spanning multiple parking bays without a forest of columns. All structural fabrication should be carried out to BS EN 1090, the harmonised standard that governs CE/UKCA marking of structural steelwork, with the execution class (typically EXC2 for this type of canopy) defined at design stage. Sections are hot-dip galvanised to BS EN ISO 1461 after fabrication, giving a zinc coating measured in tens of microns that protects the steel for decades in a typical UK environment. Bolted connections use galvanised or stainless fixings to avoid galvanic corrosion. S355 plus a proper EN 1090 paper trail is what separates a structure a building-control officer signs off quickly from one that triggers questions. Specifying this correctly up front avoids costly re-engineering later.

Foundation types: pad-and-screw versus piled

The foundation is chosen from a ground investigation, never assumed. The two families we use most are concrete pad foundations and piled or ground-screw foundations. Pad foundations are reinforced concrete blocks cast below ground that resist the overturning and uplift forces through their own mass and footprint, robust and well understood, but they involve excavation, spoil removal and concrete pours that extend the programme. Ground screws and driven piles are increasingly our preferred route on suitable ground: large helical or driven steel screws wind into the soil to transfer load, install in minutes per screw, generate almost no spoil, and can be load-tested on site immediately. The benefits of ground screws are real, faster installation, minimal concrete and easier removal, but the right answer is always ground-condition-led. Our rule is simple: the geotechnical survey decides the foundation, not the brochure. Existing car park slabs and buried services also shape the final layout.

Wind and snow loading to Eurocode EN 1991

Loading is where carport engineering gets serious, and it is governed by the Eurocodes. Wind actions are calculated to BS EN 1991-1-4 using the site's geographic location, terrain category, altitude and the canopy's height and exposure. An open-sided canopy experiences strong net uplift, so wind frequently governs the foundation design rather than gravity loads. Snow loads follow BS EN 1991-1-3, with the characteristic ground snow load varying by region and altitude across the UK. We combine these with the dead load of the steel and modules and any imposed loads per BS EN 1990's combination rules. The output drives section sizes, connection design and, critically, the uplift the foundations must resist. This Eurocode depth is precisely what the generalist pages and product catalogues omit, and it is non-negotiable for sign-off. An under-designed canopy does not announce itself on a calm day, it fails in the first serious storm, which is why we never value-engineer the load cases.

Column layouts, spans and clearance heights

Layout is a balance between structural efficiency and how the car park actually works day to day. A single-cantilever arrangement puts one row of columns down the centre or edge of a bay run and cantilevers the canopy out, maximising clear parking and minimising trip-hazard columns, though it demands more from each foundation. A double-post (portal) frame places columns on both sides, sharing the load and reducing foundation size but introducing more columns into the parking field. Spans are tuned to standard UK bay widths, typically grouping panels above runs of bays at roughly 1.5 kWp per parking bay so the array scales cleanly with the car park. Headroom is a hard constraint: a good design sets a minimum clearance height that accommodates cars, vans and, where required, larger vehicles, while keeping the panel tilt productive. A competent designer models the layout against vehicle swept paths and accessible bays before a single column position is fixed, so the structure never compromises how people use the car park.

Drainage, corrosion protection and detailing

The details decide whether a carport ages gracefully or becomes a maintenance liability. Drainage is engineered, not incidental: panels are pitched to shed water in a controlled direction, and integrated guttering and downpipes route rainwater away from pedestrian routes and parking bays, often discharging to existing surface-water drainage or to SuDS features where planning requires it. Concentrated run-off onto a footway is both a slip hazard and a planning objection, so we design it out. On corrosion protection, hot-dip galvanising to BS EN ISO 1461 is the baseline, with the option of a duplex system, galvanising plus a powder-coat or paint finish, for coastal or aggressive environments and for clients who want the canopy colour-matched to their brand. Cut ends and site-drilled holes are treated to maintain coating integrity. Corrosion failures almost always start at neglected details, an untreated cut edge, a ponding gutter or a dissimilar-metal fixing. Getting the detailing right is what turns a 25-year warranty into a longer-lived asset, and it is built in at design stage rather than patched later.

Single-deck versus double-deck structures

Most UK commercial carports are single-deck: one canopy level over a surface car park. They are the workhorse, simpler foundations, lower steel tonnage, faster planning, and they suit retail parks, offices, industrial sites and public-sector estates. Double-deck (or multi-storey) solar canopies add a parking deck beneath the array, dramatically increasing parking density on land-constrained sites, but they are a different engineering proposition: heavier frames, ramp structures, far greater foundation loads and a more involved planning and building-control process. Our guidance is to reach for double-deck only when land value or parking demand genuinely justifies the cost and complexity; for the majority of clients a well-designed single-deck canopy delivers the better return. Whichever route, we design the structure EV-ready, running DC stubs and cable routes at build so charge points can be added without re-excavating, and we plan around the full planning permission a carport requires under the Town and Country Planning Act 1990.

Planning, standards and how we engineer for sign-off

A solar carport needs full planning permission, determined by the local council, typically within around 8-12 weeks, and the structural design should be built to clear both planning and building control first time. Strong approval rates are a function of designing to the right standards from day one: BS EN 1090 fabrication, Eurocode loading to BS EN 1991, ISO 1461 corrosion protection, and properly evidenced foundation and drainage strategies. A sound engineering package also supports funding claims, including the Annual Investment Allowance (100 per cent first-year tax relief up to £1m) and OZEV's Workplace Charging Scheme. Bifacial panels can typically add around 5-12 per cent yield on the right canopy. To get your site's ground, wind exposure and layout assessed, request an appraisal via the /quote/ page.

Related reading: why full expensing does not cover solar · solar panels over parking bays · school car park canopies.