UK Bund Design Requirements
Bund design requirements are the engineering rules that govern how a bund is sized, constructed and finished to provide compliant secondary containment. They draw on UK statutory regulations, industry codes and Environment Agency guidance, and apply to every above-ground containment asset on UK industrial sites.
Overview of Bund Design Requirements
UK bund design and construction is shaped by a combination of statutory regulations and industry codes, primarily the Oil Storage Regulations, the Water Resources Act, COMAH, SSAFO, CIRIA C736 and BS EN 1992-3, backed up by Environment Agency PPG guidance. Across this framework, the same core design rules recur on every project we work on, and these are the rules we engineer every concrete bund design around:
110% capacity rule
the bund must hold at least 110% of the largest primary vessel within it. Where multiple vessels share a bund, the requirement is the larger of 110% of the biggest vessel or 25% of the combined volume of all vessels.
Freeboard above the design liquid level
Sufficient additional volume to absorb rainfall (typically a 24-hour design storm event), firefighting water (per PPG 18 and HSE guidance) and any wave action during a release.
Impermeable construction
The bund walls and floor must form a continuous, impermeable barrier. Concrete on its own is porous and prone to cracking, which is why a chemical-resistant lining is part of every modern compliant bund.
No drainage outlets, or valved drainage normally closed
Bunds must not be free-draining. Where drainage is fitted, valves are kept normally closed and only opened under controlled conditions with confirmation that no oil or chemical is present.
Structural integrity under hydrostatic load
The bund must be capable of holding the full design liquid level for the time required to recover the spill, without structural failure.
Suitable construction materials
Typically reinforced concrete, masonry or steel, with lining specified to match the stored chemistry.
Detail treatment at joints, penetrations and corners
Every discontinuity in the bund must be detailed to the same impermeability standard as the field of the lining. Most bund failures originate at details rather than across coatings.
Falls to a controlled collection point
Floors fall to a sump or low point so any contained liquid moves to recovery rather than pooling against a wall or column.
Inspection access
The design must allow for visual inspection, hydrostatic testing and maintenance access across the bund’s design life.
Suitable lining specification
Chemical resistance, impermeability and mechanical performance matched to the worst credible spill the bund could see, not the routine exposure.
Bund Design Requirements by Industry Sector
The headline design rules apply universally, but each sector has additional requirements layered on top. We design every bund to the relevant combination:
Oil, Gas and Petrochemical
Oil tank bunding requirements set by the Oil Storage Regulations and the Energy Institute Model Code of Safe Practice, with COMAH-tier sites carrying additional fire and capacity expectations.
Chemical Processing
Bund design driven by COSHH, COMAH and chemical-specific compatibility, with site environmental permits often setting higher capacity and integrity expectations than the baseline framework.
Food & Beverage
Design rules supplemented by hygiene requirements (BRCGS, HACCP, Annex 1), with falls and surface finish forming part of the production-area specification.
Agriculture & Aquaculture
Bund design under the SSAFO Regulations for slurry, silage and agricultural fuel oil, with nitrate vulnerable zone (NVZ) requirements adding capacity rules in some regions.
Sewage and Waste Water Treatment
Design rules supplemented by water industry standards (WIMES, Sewers for Adoption) and sector-specific guidance from WRc and UKWIR.
Power Generation and Transmission
Transformer bund design and standby fuel compounds governed by ENA Technical Specifications, ESQCR and operator-specific standards alongside the Oil Storage Regulations.
Nuclear Facilities
Bund design under the ONR Licence Condition framework, BS 4247 for decontaminable surfaces and site-specific specifications at Sellafield, Dounreay and the wider NDA estate.
Related Regulations
UK bund design requirements do not sit in isolation. The wider regulatory framework that informs and enforces them includes:
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PPG Guides — Environment Agency, NIEA and SEPA Pollution Prevention Guidelines, setting the practical benchmark for bunded area requirements. -
COSHH and HSE Compliance — workplace safety obligations covering chemical handling and the operatives working in or around bunded areas.
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Water Resources Act and EA Guide — the legal framework for protection of controlled waters, with offences and enforcement powers attached.
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Oil Storage Regulations (England, Scotland, Wales, Northern Ireland equivalents) — the statutory framework for above-ground oil storage and bund construction.
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COMAH Regulations 2015 — major-hazard chemical site obligations, including containment integrity as a core safety control measure.
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SSAFO Regulations — Silage, Slurry and Agricultural Fuel Oil Regulations, setting design and capacity rules for farm storage.
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CIRIA C736 — the principal industry reference for bund design, capacity, freeboard and detailing.
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BS EN 1992-3 — design of concrete structures for retaining liquids, applicable to new build bund construction.
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BS 8007 / BS 8500 — concrete specification and exposure class requirements for bunded structures.
Frequently Asked Questions
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Yes, bund design requirements apply to both new and existing installations, and grandfathering of older bunds is rare in UK practice. Existing bunds are expected to be brought up to current standards through planned refurbishment, particularly when ownership changes, environmental permits are renewed or material changes are made to the asset.
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Yes, most existing bunds can be upgraded to meet current design standards through a combination of structural reinforcement, fall correction, lining replacement and detail rework. The right approach depends on the gap between the existing asset and the current specification, and we typically scope this through a compliance review and gap analysis before any work begins.
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The principal risks are containment failure, prosecution following a release, insurance void on the affected loss, loss of operating permits, and personal director liability under environmental and workplace safety law. Outdated designs also tend to fail at detail level, such as joints, penetrations and corners, long before the operator expects, which is when older assets become an unplanned cost.
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The operator is normally required to bring the bund up to standard within a defined timescale, often through an enforcement notice or permit condition. We help operators close out non-compliant bunds by issuing an engineering specification, supervising the remediation and producing the evidence pack the regulator needs to confirm the asset is back inside the framework.
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Impermeability is demonstrated through a documented bund design and construction record, a written lining specification, application records confirming installation followed the spec, holiday (spark) testing of the lining, hydrostatic (wet) testing of the completed bund, and an ongoing inspection log. Each of those elements has to be on file and traceable when a regulator asks.
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The 110% rule is a long-established and well-understood expectation across the Environment Agency, HSE, ONR and sector regulators, and shortfalls are routinely flagged at inspection. On COMAH and PPC sites, capacity is typically tested by calculation against permit conditions, and operators should expect remedial enforcement on any bund where the volume cannot be demonstrated.
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Yes, hazardous substances trigger tighter capacity, integrity, drainage and inspection requirements, often with site-specific permit conditions on top of the baseline framework. Non-hazardous substances may still need bunded containment under PPG and CIRIA guidance, but with lower documentation expectations and less aggressive inspection cycles in most cases.
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Yes, inadequate maintenance is its own enforcement and prosecution risk, separate from the original design or installation. UK regulators routinely cite missing inspection records, unrepaired defects and overdue integrity tests as evidence of non-compliance, and operators are expected to demonstrate ongoing care of bunded assets across their full design life.
Need Help With Compliance?
Talk to our team about specifying a bund lining system that meets your regulatory obligations.
