Do Bunded Oil Tanks Need a Base?

When installing a bunded oil tank, one of the key questions is: does it require a base? The answer is unequivocally yes. A solid, level foundation is essential for stability, safety, and compliance with UK regulations. In this guide, we’ll walk you through why a base is necessary, what materials and dimensions it should meet, and how to prepare your site fully.

What Is a Bunded Oil Tank?

A bunded oil tank contains both an inner tank (holding the oil) and an outer bund designed to catch leaks or spills. This arrangement drastically reduces environmental risk and is often required by law, especially for large or hazardous storage setups.

Why the Base Is Critical

A proper base ensures:

  • Weight Support: A tank, especially when full, can weigh several tonnes. A stable foundation prevents sinking and damage.

  • Structural Stability: Without a level base, the tank may shift or buckle.

  • Compliance Assurance: UK guidelines mandate a non-combustible base extending at least 300 mm beyond all sides, able to support the tank under all conditions.

The UK government’s Environment Agency emphasizes the need for such robust secondary containment and appropriate foundations. (Environment Agency – Oil Storage Regulations)

Dimensions, Materials & Ground Preparation

Approved Materials

  • Concrete slabs – durable and stable; typically 100 mm thick.

  • Paving slabs – acceptable if laid over a properly compacted hardcore foundation.

Installation Steps

  1. Clear the site—remove debris and vegetation.

  2. Level and compact the ground.

  3. Lay a hardcore sub-base (approx. 50 mm).

  4. Install a concrete or paving slab base extending at least 300 mm beyond the tank on all sides, and check for secure load-bearing capacity.

  5. Leave room for maintenance, fuel delivery access, and drainage.

OFTEC also stresses that the base should be non-combustible and designed to minimize fire and pollution risks. (OFTEC Guidance)

Consequences of an Improper Base

Neglecting a proper foundation may result in:

  • Structural shifting or oil leaks

  • Environmental contamination

  • Violations of regulations, potentially leading to fines

  • Increased maintenance costs or premature tank failure

Summary & Where to Study Further

In short: a properly installed base is essential to your bunded oil tank’s safety and longevity. It helps avoid environmental hazards and ensures you’re fully compliant. For further help, visit our Technical Advice & Installation FAQs and explore our Bunded Oil Tank Collection to find models ready for safe, secure installations.