How long does galvanised steel last?
There is no single answer to “how many years?”. Galvanised steel is protected by a thin layer of zinc, and that is used up at a rate that depends on the air around it. But you can work out the order of magnitude.
- Sheet
- Life of galvanised steel
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- advice article
The calculation step by step
- Zinc thickness. Ordinary sheet for sheet-metal items has a Z275 coating. Under EN 10346 that is 275 g/m² in total on both sides, typically about 20 µm per side.
- Corrosion rate. ISO 9223 places environments in categories C1 to CX and gives the corrosion rate of zinc in the first year.
- Divide. Thickness ÷ rate = the approximate number of years before the coating on one side is used up.
| Environment (ISO 9223) | Zinc, µm per year | Z275 (20 µm), roughly |
|---|---|---|
| C2 – countryside, small towns | 0.1–0.7 | 29 years or more |
| C3 – towns, moderate pollution | 0.7–2.1 | 9–29 years |
| C4 – industry, salt | 2.1–4.2 | 5–9 years |
What paint does
Pre-painted (coated) sheet has an organic coating over the zinc. As long as the paint is intact, the zinc is hardly used up at all. That is why manufacturers give warranties of around 30 years on pre-painted rainwater systems (Ruukki: 30 years on the GreenCoat RWS Pro system, warranty certificate 09/2026). The warranty comes with conditions – above 900 m above sea level Ruukki halves the periods, and it excludes, for example, industrial zones.
What shortens its life
| Influence | Why |
|---|---|
| water from copper | dissolves zinc; copper above galvanised steel is ruled out |
| cut edges, scratches | steel without protection; corrosion spreads under the paint |
| cutting with a grinder, swarf | burnt-through zinc and paint, rust spots |
| standing water | a gutter with no fall, a flat parapet top |
| industry, road salt, the sea | a higher corrosivity category |
| acidic run-off | unprotected bitumen membranes, moss, old tiles |
How to make it last longer
Clean gutters and valleys regularly, touch up damage with the manufacturer’s paint, do not combine it with copper, and when replacing, consider pre-painted sheet rather than plain galvanised. Comparison with the other metals: Materials.
Questions and answers
- How many years will a galvanised steel gutter last?
- With a Z275 zinc coating (about 20 µm per side) and a zinc corrosion rate of 0.7–2.1 µm per year in an urban C3 environment under ISO 9223, it comes out at roughly 9 to 29 years until the coating on one side is used up. Longer in the countryside, shorter in industrial areas. This is a rough calculation, not a guarantee.
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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