Aluminium vs galvanised steel
For window sills, gutters and trims, the choice most often comes down to aluminium or pre-painted galvanised steel. Both can be painted the same colour, but they behave differently.
- Sheet
- Aluminium vs galvanised
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- advice article
Comparison
| Property | Pre-painted galvanised steel | Pre-painted aluminium |
|---|---|---|
| core | steel | aluminium alloy |
| corrosion protection | zinc + paint; steel exposed at cut edges | aluminium does not rust; paint is both decorative and protective |
| thermal expansion (KJG) | 0.12 mm/m per 10 K | 0.24 mm/m per 10 K |
| gutter thickness (KJG) | 0.55 mm | 0.70 mm |
| gutter, girth 333, KJG 8/2026 | €7.93 per m excl. VAT | €8.70 per m excl. VAT |
| weight | higher | lower |
| below copper | unsuitable | unsuitable |
When aluminium
- window sills – aluminium is the standard for them; it does not rust even at cut edges or in long-term contact with damp render,
- coastal or more aggressive environments, where zinc would be used up faster,
- when weight matters, for example on lightweight structures.
When galvanised steel
- flashings and trims for metal roofing made of steel sheet – the same material, colour and behaviour,
- long components, where aluminium’s high expansion is a problem,
- when cost decides it, with plain galvanised steel (gutter, girth 333, €4.20 per m excl. VAT).
What to watch with both
- expansion – twice as much with aluminium,
- no run-off from copper (Lysaght, RHEINZINK),
- cut with snips, not a grinder,
- touch up scratches.
Other metals compared: material comparison.
Technical sources
The sources this sheet draws on. We checked prices and values from standards on the date shown; for prices, whatever the source currently states always applies. Sources marked “in Slovak” or “in Czech” are only available in that language.
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