Single-skin vs bunded oil tank: which do I need?

What is a bunded oil tank?

A bund is secondary containment. It is a second barrier around the tank that holds any oil that escapes. The building regulations guidance, Technical Guidance Document J (TGD J), describes a bund as a catchpit with no drain, made of non-permeable materials, that can hold the whole contents of the tank plus an extra 10%.

Most domestic bunded tanks today are integrally bunded. Irish manufacturer Carbery describes this as a tank within a tank. The oil sits in the inner tank and the outer tank is the failsafe. A single-skin tank can also be bunded by building a sealed masonry or concrete bund around it, though this is less common at homes.

A single-skin tank has one wall. If it splits, or a fitting at the bottom fails, the oil goes straight onto the base and into the ground.

Single-skin vs bunded: the practical differences

Leaks. A crack in the inner wall of a bunded tank is caught by the outer one. A crack in a single-skin tank lets oil out.
Base. TGD J says a tank without a bund should stand on a non-combustible base that extends at least 300 mm beyond every side. Non-combustible bases can be concrete at least 100 mm thick, paving slabs at least 42 mm thick, or a purpose-built stand.
Size on the ground. A bunded tank is bigger and heavier than a single-skin tank of the same capacity, so measure the space before you order.
Price. We have not found an independent Irish source for tank prices, so compare written quotes for both types.

When does an oil tank need to be bunded in Ireland?

The legal requirement is Part J of the Building Regulations. Requirement J6 says a fixed oil tank serving a heating appliance, and its pipes, must be located, built and protected to reduce to a reasonable level the risk of oil escaping and causing pollution. TGD J explains how to meet that. Its 2014 version applies to works that started on or after 1 September 2014.

For a tank of up to 3,500 litres, TGD J says secondary containment is needed:

for any tank inside a building, which must also be in a fire-rated chamber;
for any tank wholly below ground;
for an outdoor tank over 2,500 litres;
for any outdoor tank where a leak would be a significant risk of water pollution.

TGD J says a significant risk of water pollution is likely where the tank is:

within 10 metres of a river, stream, lake or other inland water, or coastal water;
where spilt oil could run into an open drain or a loose-fitting manhole cover;
within 50 metres of a drinking water source such as a well, borehole or spring;
where spilt oil could run across hard ground to any of those waters;
where the vent pipe outlet cannot be seen from the filling point.

An outdoor tank of 2,500 litres or less at a house, with none of those risks, does not generally need a bund under TGD J. Tanks over 3,500 litres follow BS 5410 Part 2. If your home has a private well, measure the distance before you assume a single-skin tank is allowed.

Building control rules and local conditions vary. If you are unsure, check with your local authority's building control section and ask your installer to put their assessment in writing.

Do I have to replace my single-skin tank?

No rule we found makes you swap a sound single-skin tank just because it is single-skin. The guidance applies when you fit a new or replacement tank. When your current tank shows its age, that is the time to move to bunded if your site needs it. See signs your oil tank is leaking and when to replace it.

Even where a bund is not required, Clare County Council suggests considering a bunded tank or a leak detection alarm.

Where can an oil tank go? Fire distances

TGD J and OFTEC set out how far an outdoor tank of up to 3,500 litres should be from things that could catch fire:

1.8 metres from any part of a building, or a fire barrier and fire-resisting construction if closer;
1.8 metres from an oil boiler or its flue terminal, or a fire barrier between them;
760 mm from a boundary, or a fire barrier or boundary wall at least 300 mm higher and wider than the tank.

A barrier in TGD J means a wall or screen with at least 30 minutes' fire resistance. OFTEC adds that a tank inside a garage or outhouse needs a 60-minute fire-rated chamber.

Plastic or steel oil tank?

Both are allowed. TGD J says tanks should meet OFTEC's specifications: OFS T100 for plastic tanks, with polyethylene tanks tested to I.S. EN 13341, and OFS T200 for steel tanks, bunded or not.

They age differently. Clare County Council says to check plastic tanks for splits, cracks and sun bleaching, and metal tanks for rust patches. Zurich Ireland warns that a tank without full horizontal support can warp and crack over time.

What size oil tank do I need?

Common home sizes run from about 650 to 2,500 litres. Carbery's bunded range includes 650, 1,000, 1,100, 1,350 and 2,500 litre models, and its single-skin range runs from 650 to 2,500 litres. Remember that a tank over 2,500 litres needs secondary containment under TGD J.

A bigger tank means fewer deliveries and lets you buy more when prices dip. Oil is heavy too. OFTEC says 1,000 litres weighs just under a tonne, so the base must be solid and level. To size it from your own usage, see how much heating oil do I need?

Do insurers require a bunded tank?

We found no Irish rule that says so, but policies differ. OFTEC warns that home insurance often covers lost oil and damage to the house but limits clean-up of contaminated ground. Ask your insurer whether tank type, age or inspection affects your cover before you choose.

What to ask an oil tank installer

Are you OFTEC-registered? You can check on the OFTEC register.
Does my site need a bunded tank under TGD J, and will you put that in writing?
How far will the tank be from the house, the boiler flue, the boundary, drains, water and any well?
Does the tank meet OFS T100 or OFS T200, and what is the warranty?
Is the base included, and is the existing base good enough?
Will you remove and dispose of the old tank and any oil left in it?
Will the fuel line have an automatic fuel cut-off (fire) valve? TGD J says one should be fitted.
Will the tank have a label explaining what to do if it leaks? TGD J suggests one.
Can you quote the tank, base, removal, pipework and VAT as separate lines?

Common questions

What is the difference between a single-skin and a bunded oil tank?

A single-skin tank has one wall. If it cracks, oil escapes. A bunded tank has a second outer tank, or sits in a sealed bund, that can hold the full contents plus 10%. A leak from the inner tank is caught instead of soaking into the ground.

Do I need a bunded oil tank in Ireland?

For a new or replacement tank, Technical Guidance Document J says secondary containment, such as a bunded tank, should be provided if the tank holds more than 2,500 litres or there is a significant risk of water pollution. That includes being within 10 metres of a river, stream, lake or the sea, within 50 metres of a well, borehole or spring, or where spilt oil could run into an open drain.

Do I have to replace my single-skin tank?

Not just because it is single-skin. The 2014 guidance applies to works that started on or after 1 September 2014. If your tank is sound and well sited, it can stay. When it does need replacing, your installer should check whether the new one must be bunded.

Is a plastic or steel oil tank better?

Both can meet the rules. TGD J points to OFTEC standard OFS T100 for plastic tanks and OFS T200 for steel tanks. Plastic tanks need checking for cracks, splits and sun bleaching. Steel tanks need checking for rust. Ask your installer which suits your site.

Next step

Time a tank swap for when your tank is nearly empty, then fill the new one. The heating oil planner estimates when you will run low, and you can compare local oil suppliers for the first fill.

General guidance for the Republic of Ireland, checked against TGD J (2014) on 10 October 2026. It does not cover Northern Ireland.