Building Regulations Approved Document J sets minimum separation distances between oil storage and buildings, boundaries and other hazards. Where the distances cannot be achieved, fire protection must be provided instead. The base must support the tank full and extend beyond its footprint.
The separation distances and why they exist
A domestic oil tank holds a large quantity of a combustible liquid, usually within a few metres of a house. The separation requirements exist so that a fire in the tank cannot readily spread to the building, and a fire in the building cannot readily reach the tank.
| Separation from | Why |
|---|---|
| Any non-fire-rated part of a building – doors, windows, eaves, cladding, vents | A tank fire must not be able to enter the building through an opening or ignite combustible cladding or soffits |
| The boundary of the property | Protects the neighbouring property, and yours from theirs |
| Flue terminals and other ignition sources | Self-evident |
| Combustible screening, fencing and vegetation | Timber fencing and hedging burn, and are routinely overlooked because they were planted afterwards |
The distances are specified in Approved Document J and in the OFTEC technical guidance that installers work to. The important practical point is that they are measured to specific features – an eaves overhang, a window opening, a boundary line – and not to a general sense of where the house is.
A tank correctly sited in 2006 can be non-compliant now because somebody built a fence, planted a hedge, added an extension, or fitted a new window in the nearest wall. Nobody reassesses it, because from the tank’s point of view nothing changed. It is worth measuring if any of those have happened.
When the distances cannot be met
On many sites, particularly smaller gardens and terraced properties, the required separation is simply not achievable. That does not make a tank impossible – it means fire protection must be provided instead.
The standard solution is a fire barrier: a wall or screen of masonry or other suitable non-combustible construction, with a specified fire resistance, positioned between the tank and the thing it must be separated from, and extending beyond the tank in each direction and above it.
- It must be imperforate – a barrier with a gap in it is not a barrier.
- It must have the specified fire resistance, which means real construction rather than a decorative screen.
- It must extend beyond the tank’s extent horizontally and vertically, so fire cannot go round or over it.
- It can be an existing wall if that wall genuinely has the required resistance, which a masonry house wall frequently does – and a timber-clad or rendered lightweight wall does not.
A fire barrier is real construction and it is not cheap, but it is considerably cheaper than moving a tank later. It is far better to design one in at the start than to discover the need after the tank has been delivered.
The base
More tanks fail because of their base than for any other reason. A full 1,360 litre tank plus the weight of the tank itself is well over a tonne on a small footprint, sitting there for twenty years through frost, heave and saturated Norfolk clay.
A base done properly is:
- Non-combustible – concrete, or paving slabs correctly laid on a prepared sub-base. Not timber, not railway sleepers.
- Level, and staying level. A plastic tank on an uneven base is being twisted continuously, and that is precisely how stress cracks form.
- Capable of supporting the tank full, on a prepared sub-base rather than on soft ground.
- Extending beyond the tank on every side – typically at least 300mm – so the tank is fully supported and the edges are not overhanging.
- Draining away from the tank, so water does not sit underneath it. Standing water under a steel tank is how the base corrodes.
- Suited to the tank type. A steel tank bears on specified support points rather than sitting flat, and the base must suit that.
Slabs bedded on sand will move. It is the single most common shortcut and it shortens a tank’s life by years.
Access, delivery and the practical constraints
- The tanker has to reach it. Delivery hose reach is finite. A tank at the bottom of a long garden with no vehicle access is a tank that cannot be filled, or one that requires a surcharge every time.
- The vent outlet should be visible from the fill point, so an overfill can be seen. Where it cannot be, an overfill prevention device becomes the sensible answer.
- The fill point needs to be accessible and, ideally, lockable. Heating oil is stolen.
- Sun exposure matters for plastic tanks. A south-facing position in full sun degrades polyethylene faster than a shaded one.
- Trees are a mixed blessing – shade is good, roots and falling branches are not.
- Frost pockets and standing water are worth avoiding for the base’s sake.
Bunding is a separate question
Separation distances are about fire. Secondary containment – bunding – is about pollution, and it is decided by a different assessment entirely. A tank can be perfectly sited for fire separation and still require bunding because it is near a ditch.
The two assessments happen together at survey but they answer different questions, and it is worth being clear which is which. See bunded or single-skin and oil tank installation.
Planning a tank, or wondering whether yours still complies? The measurements take ten minutes on site.
Questions we get asked about this
Do I need planning permission for an oil tank?
Domestic tanks are usually permitted development within limits on capacity and position, with exceptions for listed buildings, conservation areas and positions forward of the principal elevation. The local planning authority is the definitive answer for your property.
Can I put a fence round my tank?
Only if it respects the separation distances – timber fencing is combustible and counts as something the tank must be separated from. A non-combustible screen, or a proper fire barrier, is a different matter.
What if my tank does not meet the distances?
Fire protection is provided instead, typically a fire barrier wall with the required resistance. It is a legitimate solution and it needs to be designed rather than improvised.
How thick does the base need to be?
It needs to support the tank full on a prepared sub-base, level, non-combustible, and extending beyond the tank on all sides. The specific construction depends on the ground and the tank, which is why it is assessed rather than assumed.
Can the tank go against the house wall?
Only if that wall has the required fire resistance over the necessary extent and there are no openings within the separation distance. A solid masonry wall with no windows or doors nearby frequently qualifies; a wall with a window above it does not.
Does the existing tank have to be moved if it does not comply?
A tank installed compliantly under earlier requirements is generally not required to be moved simply because guidance has changed. A replacement is a different matter – it is a new installation and it is assessed against current requirements.
Regulations and standards referenced on this page
- Approved Document J: combustion appliances and fuel storage systems — Ministry of Housing, Communities and Local Government
You might also need
- Bunded or single-skin? How to tell which tank you are allowed
- Buying heating oil: order size, timing and tank management
- Eight signs an oil tank is near the end of its life
- Frozen condensate pipes: why it happens and how to stop it recurring
- Grant, Firebird, Warmflow, Worcester Danesmoor and Mistral, compared honestly
- Internal, external or boiler house: where an oil boiler should go
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.