Steel vs aluminium roller doors in Scottish conditions
The steel-or-aluminium question looks like a simple one until you factor in where the door actually sits. A galvanised steel shutter that will last 20 years in a dry industrial estate in Perthshire will visibly pit inside five years on a west-facing elevation 200 metres from Loch Broom. This page walks through the trade-offs that matter in Scottish conditions.
Corrosion: what actually fails, and when
Scottish weather is relatively mild on metals until you add salt. The UK's BS EN ISO 9223 corrosion-category map places inland Highland glens in category C2 (low), most of the east coast in C3 (medium), and the Hebridean, Orcadian, and exposed western coastlines in C4 (high). A few headland sites on Lewis, Skye, and Shetland reach C5.
What those categories mean in practice:
- Standard galvanised steel shutter (Z275 coating). Comfortable for 20+ years in C2. Visible rust spotting within 5–8 years in C4 without repainting. Realistic maintenance life 10–12 years on exposed coasts.
- Galvanised steel with polyester powder-coat. Adds roughly 5 years to the life of the first repaint cycle. Chips and scratches become rust initiation points, so a fitter who touches up during install matters.
- Aluminium with polyester powder-coat. Aluminium forms a self-healing oxide layer. Coating failure is cosmetic rather than structural. Realistic life on the Western Isles is 20 years before any refurbishment conversation.
- Stainless steel fixings. Non-negotiable on any C4 or C5 site. Galvanised machine screws through aluminium or steel in salt air pit out inside three years and cause bimetallic rust streaks down the curtain.
Insulation: where aluminium pulls ahead
Domestic roller garage doors are almost always twin-wall aluminium with injected polyurethane foam. The standard 77 mm insulated slat from SeceuroGlide, Gliderol, and Hörmann posts a published U-value around 1.1–1.4 W/m²K for the curtain, giving a whole-door U-value (including guides and box) of roughly 3.5–4.5 W/m²K. That is not remarkable against a modern sectional door, but it is a significant step up from a single-skin steel shutter's 6+ W/m²K and from an old up-and-over.
For any garage that shares a wall with a heated room — a common Scottish arrangement with integral garages underneath bedrooms — an insulated aluminium roller door is what stops the garage becoming a cold radiator on the other side of that wall.
Weight, head-room, and the practical stuff
Aluminium slats are roughly a third of the weight of equivalent steel. That has three consequences:
- Smaller motors. A domestic 2.4 m aluminium curtain runs on a 230 V single-phase tubular motor. Steel curtains above 3 m usually need a three-phase side-motor with external gearbox.
- Smaller head-box. Aluminium coils onto a 205 mm barrel; steel needs 250–300 mm depending on slat depth. For an integral garage with a low lintel, aluminium is sometimes the only option that physically fits.
- Hand-winding is viable. You can winch an aluminium curtain shut by hand in a power cut. Hand-winding a 4 m steel shutter is possible but not pleasant.
Cost per opening
The headline numbers (see our full cost guide) put aluminium domestic doors at £1,200–£2,800 supplied and installed, and galvanised steel commercial shutters at £1,200–£6,500. But for like-for-like openings the picture is narrower:
- For a 2.4 × 2.1 m opening, an insulated aluminium door comes in around £1,400 fitted; a single-skin galvanised steel shutter, around £1,300. The price difference reverses once you add security lath or insulation to the steel option.
- For a 4 × 3 m commercial opening, a steel shutter is £900–£1,500 cheaper than the equivalent aluminium — and most commercial specifications don't need the thermal performance anyway.
- For a 5 × 5 m+ industrial opening, aluminium becomes structurally awkward — the curtain gets heavy, the slat depth has to increase, and steel is both cheaper and stiffer.
Lifespan and maintenance
Assume 15–20 years of service for either material, provided:
- The door is serviced annually (guides cleaned, motor torque checked, springs greased).
- Coastal sites get a fresh-water rinse of the curtain and guides every few months in winter — a hose and a sponge, not a pressure washer, which drives salt into the slat joints.
- Any coating chips are touched up with the manufacturer's repair paint within a week, particularly on steel.
Realistic retirement is driven by motor failure rather than curtain failure. The typical tubular motor in a domestic door has a rated cycle life of around 10,000 cycles, which in a household using the garage twice a day is roughly 14 years. Industrial motors with thermal overload protection and oil-bath gearboxes reach 25+ years on normal duty cycles.
The short recommendation by site type
| Site | Recommended | Why |
|---|---|---|
| Integral domestic garage, inland | Insulated aluminium | Thermal performance, quiet motor, low head-room |
| Detached domestic garage, coastal | Insulated aluminium, marine-grade coating | Corrosion life, low weight for hand-winding |
| Urban shopfront | Powder-coated galvanised steel | Security, cost per metre, aesthetic lath options |
| Rural lock-up, east coast | Galvanised steel, punched lath | Ventilation, security, cost |
| Exposed Island commercial unit | Aluminium or coated stainless lath | C4/C5 corrosion category makes plain galv uneconomic |
| Agricultural barn > 5 m | Galvanised steel, insulated lath if heated | Structural stiffness at span, cost |
Most buyers don't actually have to choose — the opening size and the duty cycle pick one of the two materials for them. The value of asking the question is that it flushes out whether your installer has thought about corrosion category and thermal performance for your specific site, rather than quoting the same default product to everyone.