Steel vs Aluminium Solar Carport Frames: A Materials Comparison for UK Projects
- Keith Lin
- Mar 24
- 5 min read
Updated: Apr 9
Last updated: 24 March 2026
For commercial solar carports in the UK, hot-dip galvanised structural steel is the industry standard frame material. It offers superior strength-to-cost ratio, longer clear spans between columns, and proven durability in the British climate. Aluminium is lighter and naturally corrosion-resistant, but it is more expensive and less suited to the wide-span, heavy-load requirements of commercial car park canopies.
Why the Frame Material Matters
The structural frame is the single most expensive component of a solar carport — typically 40–55% of total project cost. The choice between steel and aluminium affects not only the upfront price but also the structural performance, maintenance requirements, installation process, and design life of the entire system.
For UK commercial projects, this decision should be driven by engineering requirements, not marketing. Both materials are well-proven in construction. The question is which one delivers the best performance for the specific demands of a car park canopy.
Steel vs Aluminium: Head-to-Head Comparison
Tensile strength: Steel 430–580 MPa (S355) vs Aluminium 170–310 MPa (6082-T6)
Yield strength: Steel 355 MPa vs Aluminium 240–275 MPa
Density: Steel 7,850 kg/m³ vs Aluminium 2,700 kg/m³
Elastic modulus: Steel 210 GPa vs Aluminium 70 GPa
Corrosion protection: Steel — hot-dip galvanising (zinc, 80+ µm) vs Aluminium — natural oxide layer + optional anodising
Design life: Steel 50+ years (galvanised) vs Aluminium 40+ years (anodised)
Cost per tonne: Steel £1,200–£1,800 vs Aluminium £3,500–£5,500
Fabrication standard: Steel — EN 1090-2 vs Aluminium — EN 1090-3
Structural Performance
Strength and Span Capability
Steel's higher yield strength (355 MPa vs 240–275 MPa for aluminium) and significantly higher elastic modulus (210 GPa vs 70 GPa) mean it can span greater distances between columns with lighter sections. This is critical for car park applications where columns must be positioned between parking bays, not within them.
A typical single cantilever solar carport has a clear span of 5.5–6.5 metres. In steel (S355 grade, hollow section columns, I-beam or RHS rafters), this span can be achieved with economical section sizes. In aluminium, achieving the same span requires significantly deeper and heavier sections to compensate for the lower stiffness.
Key point: Aluminium is approximately one-third the weight of steel for the same volume, but because it is also one-third the stiffness, you need roughly three times the section depth to match steel's deflection performance. For carport spans, the net weight saving is typically only 30–40%, not the 65% that raw density figures suggest.
Wind and Snow Loading
UK carport designs must comply with BS EN 1991-1-4 (wind actions) and BS EN 1991-1-3 (snow loading). Steel's higher strength-to-stiffness ratio makes it the preferred material for resisting these dynamic loads. The connection design is simpler and more economical in steel, and the foundation loads are more predictable.Corrosion Resistance
Steel: Hot-Dip Galvanising
Standard practice for UK solar carport steelwork is hot-dip galvanising to BS EN ISO 1461. The process involves immersing the fabricated steelwork in molten zinc at approximately 450°C, creating a metallurgically bonded zinc coating of 80–100 µm thickness.
This coating provides: barrier protection (zinc physically separates the steel from moisture and oxygen), cathodic (sacrificial) protection (zinc corrodes preferentially, protecting the steel even where the coating is scratched), and self-healing (minor damage is repaired by surrounding zinc through galvanic action).
In a typical UK environment (C3 corrosivity category per BS EN ISO 9223), hot-dip galvanised steelwork has a maintenance-free life of 50–70 years before first maintenance is required.
Aluminium: Natural Oxide Layer
Aluminium forms a thin aluminium oxide (Al₂O₃) layer naturally when exposed to air. This passive layer provides excellent corrosion resistance without any applied coating. For enhanced durability, aluminium carport frames can be anodised or powder-coated.
Advantage: Aluminium does not require a protective coating for corrosion resistance. However, aluminium is susceptible to galvanic corrosion when in contact with dissimilar metals (particularly steel fasteners) — a common issue in mixed-material assemblies.
Cost Comparison
For a typical 50-bay commercial solar carport:
Steel Frame: Raw material £45,000–£65,000 + Fabrication £25,000–£35,000 + Galvanising £8,000–£12,000 + Transport £3,000–£5,000 = Total £81,000–£117,000
Aluminium Frame: Raw material £85,000–£130,000 + Fabrication £35,000–£50,000 + Anodising £5,000–£10,000 + Transport £2,000–£4,000 = Total £127,000–£194,000 (+57–66% premium)
The primary cost driver is raw material. Aluminium alloy costs roughly 2.5–3× more per tonne than structural steel. Foundation savings from aluminium's lower weight are typically only £3,000–£8,000 on a 50-bay project — not enough to close the gap.
When Aluminium Makes Sense
Coastal and Marine Environments
Within 1 km of the coastline (C4–C5 corrosivity categories), aluminium's natural corrosion resistance outperforms galvanised steel. The aggressive salt-laden atmosphere accelerates zinc depletion, reducing the maintenance-free life of galvanised steel to 15–25 years.
Architectural Sensitivity
Where the carport is in a prominent location with strict aesthetic requirements (heritage settings, prestigious corporate headquarters), aluminium's clean finish and availability in anodised or powder-coated colours may be preferred.
Small-Scale Residential Applications
For domestic solar carports (1–2 bays) where spans are short and loads are light, aluminium's ease of handling may outweigh the cost premium.
When Steel Is the Clear Choice
Standard Commercial Car Parks
For the vast majority of UK commercial solar carport projects — office car parks, retail parks, warehouses, distribution centres, fleet depots, schools, hospitals — steel delivers the best combination of structural performance, cost efficiency, and proven durability.
Large-Span Configurations
Double cantilever systems with 12–14 metre total spans are standard in steel but challenging and expensive in aluminium.
Multi-Site Rollouts
Where standardised designs are being deployed across a portfolio of sites, steel's cost advantage compounds. A 10-site rollout could save £400,000–£700,000 by choosing steel over aluminium.
EN 1090-1 Compliance
The EN 1090-1 supply chain for structural steel in the UK is mature and well-established, with numerous certified fabricators. The aluminium EN 1090-3 supply chain is smaller and less competitive.
KLY Solar's Position
KLY Solar supplies EN 1090-1 certified hot-dip galvanised structural steel carport frame kits as standard. We chose steel for the same reasons most structural engineers specify it for commercial canopies: it delivers the best strength, span capability, durability, and value for UK car park applications.
All our frames are manufactured to Execution Class 2 (EXC2) with full structural engineering calculations, CE/UKCA Declaration of Performance, and comprehensive installation documentation.
Ready to specify a steel carport frame for your project? View our solar carport systems
About the Author
Keith Lin is the Director of KLY Solar (KLY Global Ltd), a UK supplier of solar carport structure kits for commercial project teams.
Sources cited in this article:
KLY GLOBAL LTD trading as KLY Solar | Company No. 14169672
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