A new domestic oil tank has to be risk-assessed for secondary containment, sited to the separation distances in Building Regulations Approved Document J, and stood on a base that will support it full. Whether you need a bunded tank is determined by that assessment, not by preference – and getting it wrong is an expensive thing to discover later.
The risk assessment comes first
Before anything is ordered, the installation has to be risk-assessed. The assessment determines whether the tank must have secondary containment – a bund, effectively a tank within a tank – and where it can legally stand. It is not a formality and it is not a preference, and the answer frequently surprises people.
Secondary containment is required where a spillage or leak could reasonably reach the environment or a building. In practice, an integrally bunded tank becomes necessary where any of the following apply:
- The tank stands within 10 metres of a watercourse, ditch, pond or any other controlled water.
- A spillage could run into or reach a drain, gully, manhole or soakaway.
- The tank is within 50 metres of a borehole, spring or well used for drinking water.
- The tank sits on hard standing that would channel a spill rather than contain it.
- The vent pipe outlet cannot be seen from the fill point, so an overfill would not be noticed.
- The tank capacity is above the domestic threshold at which bunding becomes mandatory regardless of location.
Norfolk being Norfolk, the watercourse clause catches a great many properties. Field ditches, dykes and drainage channels all count, and they are not always obvious from the garden. There is more on this in bunded or single-skin.
Where the tank is allowed to go
Separation distances exist because kerosene burns. Approved Document J sets out minimum distances between an oil storage tank and the things around it, and where those distances cannot be achieved, fire protection has to be provided instead – typically a wall or barrier with a suitable fire resistance rating extending beyond the tank in each direction.
| From | Why it matters |
|---|---|
| Any non-fire-rated part of a building – doors, windows, eaves, cladding | A tank fire must not be able to spread into the building, or a building fire into the tank |
| The boundary of the property | Protects the neighbour, and protects you from theirs |
| Flue terminals and other ignition sources | For obvious reasons |
| Screening, fencing and vegetation | Timber fencing and hedging is combustible and frequently forgotten |
Where the distances cannot be met, the fix is a fire barrier rather than an exemption. That is a legitimate solution, but it needs to be designed in from the start – a wall retrofitted afterwards is far more expensive than one planned at survey.
The fill point has to be accessible to a delivery tanker and the vent outlet should be visible from it. This sounds trivial until you have a tank at the bottom of a long garden and a driver who cannot see whether it is overflowing. Where the fill point is remote from the tank, an overfill prevention device becomes the sensible answer.
The base
More tanks are ruined by their bases than by anything else. A full 1,360 litre tank plus the tank itself is well over a tonne concentrated on a small footprint, and it stays there for twenty years through frost, heave and saturated Norfolk clay. Paving slabs bedded on sand will move. Once a plastic tank is standing on an uneven base it is being twisted continuously, and that is precisely how stress cracks form.
A base done properly is a level, continuous, non-combustible slab – concrete or correctly laid flags on a prepared sub-base – extending at least 300mm beyond the tank on every side, capable of supporting the tank full, and laid so water runs away rather than sitting under it. For a steel tank, the supports have to suit the manufacturer’s specified bearing points rather than the tank being dropped anywhere flat.
If you are having a tank moved to a better position, the base is where most of the work and most of the cost actually is. It is also the part that determines whether you are doing this again in eight years.
What we install and how
- Survey and risk assessmentSite walk, distances measured, drainage and watercourses identified, and a decision on bunding recorded rather than assumed.
- SizingCapacity chosen for the property’s actual annual usage and how you prefer to buy oil – larger tanks let you buy on better timing, but only if there is room and the base can take it.
- Base preparationBuilt to take the tank full, level, with the correct overhang and drainage away from the tank.
- Tank set and securedPositioned to the manufacturer’s requirements, with the correct fittings: sight or contents gauge, vent, fill point, outlet valve and filter.
- Oil line and fire valveNew supply line in the correct material, protected where it passes through or under structures, with a remote-sensing fire valve at the point it enters the building.
- Commission and hand overLeak checked, gauge verified, boiler recommissioned and bled, and you are shown where everything isolates.
Things worth deciding before you order
- Capacity. Bigger tanks buy you flexibility on when you fill, which matters given how oil prices move. They also need more base, more room and more separation.
- Plastic or steel. Both are legitimate. They fail differently and they suit different sites – see plastic vs steel oil tanks.
- Where the delivery driver will actually stand. Hose reach is finite. A beautiful position at the far end of the garden is worthless if the tanker cannot reach it.
- Security. Heating oil is stolen. A lockable fill cap and sensible siting cost very little at installation.
- Monitoring. Electronic level gauges that warn you before you run dry are cheap, and running dry causes far more expensive problems than the gauge costs.
Planning a new tank? The siting survey is the part that determines everything else. It is worth doing before you buy anything.
Questions we get asked about this
Do I need planning permission for an oil tank?
Domestic oil tanks are usually permitted development within limits on capacity and position, but there are exceptions – listed buildings, conservation areas, and tanks forward of the principal elevation among them. We will flag it at survey if your site looks like one of the exceptions, and the local planning authority is the definitive answer.
Do I have to have a bunded tank?
That depends entirely on the risk assessment for your specific site. A great many Norfolk properties do, because of proximity to a ditch or drainage channel. Where it is required it is required – it is not an upgrade option.
Can the tank go where the old one is?
Usually, if the old position complied and the base is sound. Where it did not comply – and older tanks frequently do not – a like-for-like replacement is not always possible. We would rather tell you that at survey than after the old tank has gone.
How big a tank should I have?
It is driven by your annual consumption, the space available and how you like to buy. A tank that lets you fill in one delivery and still hold a reserve is the practical target. We will work it out from your actual usage rather than a rule of thumb.
What happens to the old tank?
It has to be drained, cleaned and removed, and the residual oil and sludge disposed of properly. It is a genuine part of the job and it should be itemised on the quote, not discovered afterwards.
Is a tank fire barrier expensive?
It is a masonry wall with a defined fire resistance, built to extend beyond the tank. It is not trivial, but it is far cheaper than moving a tank later, and on constrained sites it is what makes a compliant installation possible at all.
Regulations and standards referenced on this page
- Approved Document J: combustion appliances and fuel storage systems — Ministry of Housing, Communities and Local Government
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.