Lego-Style Silage Clamp Construction – Compliance with Regulations

Silage clamps with walls constructed from ‘Lego-style’ interlocking concrete blocks offer a flexible, practical storage solution for many farms. These systems are quick to assemble without the need for fixing materials and can be built on either a concrete or asphalt base. One of the biggest advantages is their versatility – they can be constructed, reconstructed, or completely relocated as your storage needs change, with no foundation required.

This type of setup is ideal for both permanent and temporary storage. However, while the system may be easy to use, it must still comply with strict environmental regulations.

Regulations in England

In England, silage clamps built with interlocking concrete blocks must comply with the SSAFO Regulations Storing silage, slurry and agricultural fuel oil – GOV.UK and meet the loading standards of BS 5502: Part 22: 2003(c) as outlined below.

Silos

All parts of a silo must be resistant to attack.

Your silo must have:

• An impermeable base extending beyond any walls
• Impermeable drainage collection channels around the outside, flowing into an effluent tank

The base must comply with:

• British Standard 8007:1987 and British Standard 8110-1:1997 (for concrete bases)
• British Standard 594/EN 13108-4:2006 (for hot-rolled asphalt bases)

If your silo has retaining walls, they must withstand wall loadings set in British Standard 5502-22:2003+A1:2013 and meet the following requirements:

• The retaining walls must be capable of withstanding minimum wall loadings calculated on the assumptions and in the manner indicated by Paragraph 15.6 of the Code of Practice on buildings and structures for agriculture published by the British Standards Institution and numbered BS 5502: Part 22: 2003(c).
• The silo must at no time be loaded to a depth exceeding the maximum depth consistent with the design assumption made in respect of the loadings of the retaining walls; and
• Notices must be displayed on the retaining walls in accordance with Paragraph 18 of that code of practice.

Note: It is crucial that the above requirements are adhered to as there have been cases where this type of wall has collapsed.

Effluent tanks

Your silo must have an effluent collection system.

If all parts of an effluent tank are above ground the tank must be constructed to resist attack from silage effluent for at least 20 years with maintenance. If any part is below ground, it should be impermeable for at least 20 years without maintenance. You’ll be asked to prove your tank is suitable, for example with a manufacturer’s guarantee.

Capacity

The minimum capacity rules for effluent tanks should give you at least 2 days’ storage at peak flow. However, it’s up to you to make sure you’ve got enough capacity to avoid the risk of pollution.

You must tell the Environment Agency at least 14 days before you build new storage for silage, slurry or agricultural fuel oil, or make substantial changes to an existing store. You must also tell the Environment Agency if you intend to make or store field silage or non-baled bags – there are specific rules and a form.

Regulations in Wales

Under the Water Resources (Control of Pollution) (Silage, Slurry and Agricultural Fuel Oil) (Wales) Regulations 2010 (SSAFO), silage clamps built with interlocking concrete block walls are generally treated as ‘concrete pad’ style clamps. Since the walls are not fixed in place, the structure is considered moveable—if removed, only the base remains.

To comply with SSAFO and the Water Resources (Control of Agricultural Pollution) (Wales) Regulations 2021 (CoAPR), silage clamps constructed with ‘Lego-style’ block walls must meet the following standards:

• The clamp base, effluent tank, and drains must be impermeable and resistant to silage effluent. The base must be designed and constructed in accordance with BS 8007 or BS 5502 Part 21.
• If walls (including interlocking blocks) are used, they must be placed within the boundary of the base, which must extend beyond the walls, and include a perimeter drainage channel connected to an effluent tank.
• The effluent tank must collect and contain all runoff. It must have a capacity of 20 litres per cubic metre of silo volume (up to 1,500 m³), plus an extra 6.7 litres per cubic metre for any volume above that.
• The clamp must not be located within 10 metres of any watercourse or land drain.
• The structure (clamp and drains) must be capable of lasting 20 years with routine maintenance.
• Any below-ground effluent tanks must last 20 years without maintenance, and a certificate confirming compliant design and construction must be sent to Natural Resources Wales (NRW) 14 days before use.
• If interlocking blocks become a permanent part of the structure, they must comply fully with Schedule 5 of SSAFO, including design to BS5502 Part 22 and resistance to silage effluent.

Note: As the blocks are not fixed, care must be taken to ensure they do not shift or obstruct the perimeter channel, which would result in non-compliance.

You must also notify NRW in writing at least 14 days before using any new, substantially enlarged, or substantially reconstructed clamp. NRW provides forms to help with this process.

Key takeaways for ensuring compliance

‘Lego-style’ interlocking concrete block clamps are a practical, adaptable option for silage storage, offering speed and flexibility. But flexibility doesn’t mean freedom from regulation. These systems still need to meet stringent standards in England and Wales, including construction, drainage, and effluent containment requirements.

Whether your clamp is temporary or becoming a permanent fixture, understanding the compliance rules is essential. If in doubt, seek professional advice to avoid non-compliance and protect both your business and the environment.

Need help navigating the regulations?

Our Agricultural Compliance team is here to help. Whether you need guidance on silage clamp design, documentation checks, or advice on meeting regulatory requirements, we can support you every step of the way. Call us on 01981 590514 to speak to an adviser or find out more.