The simple explanation of double-skinned "tank within a tank" bunding — how it protects you, how it differs from single-skin, and whether you need one.
A bunded oil tank is, quite literally, a tank within a tank. An inner tank holds your heating oil, and a second outer skin — the "bund" — wraps around it. The bund is built to hold at least 110% of the inner tank's capacity, so if the inner tank ever cracks, splits or leaks, the escaping oil is caught safely inside the outer skin instead of soaking into your garden.
| Single-skin | Bunded | |
|---|---|---|
| Walls | One | Two (tank within a tank) |
| Leak protection | None — oil escapes | Outer skin contains 110%+ |
| Cost | Lower | Higher |
| Where allowed | Low-risk positions only | Almost anywhere |
| Typical use today | Rare | The standard choice |
Heating oil is a pollutant. A single split tank can contaminate soil, drains and watercourses, and the clean-up can cost many thousands of pounds — often more than the tank itself. Bunding is the insurance against that: a quiet second line of defence that protects your property, your wallet and the environment.
You'll need bunded if an site risk assessment flags a pollution risk, or if the tank holds over 2,500 litres. In practice that covers most homes — especially rural Wiltshire properties near ditches, streams, drains or boreholes. Our full oil tank regulations guide explains exactly when bunding is required.
Yes — for almost everyone. The price difference over single-skin is small compared with the cost of a pollution clean-up or a failed insurance claim, and bunded is usually the only compliant option anyway. See typical figures in our cost guide.
A tank within a tank — an inner tank holds the oil and an outer skin (the bund) holds at least 110% of the contents, so a leak from the inner tank is safely contained.
Single-skin has one wall; if it fails, oil escapes. Bunded has a second outer skin that contains any leak — which is why it's required in most modern installations.
You need bunded if a risk assessment identifies a pollution risk, or if the tank holds over 2,500 litres — which applies to most domestic properties.
We'll advise honestly on the right tank for your site. Drop us a message and someone will come back to you as soon as possible.
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