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How to Build Over a Sewer Pipe in the UK

How to Build Over a Sewer Pipe in the UK


If you’re considering extending your home or building a conservatory or outbuilding on your property, it is important to realise that this kind of work can have an impact on the underground sewer pipes, gas pipes, and main water pipes which lie within your property’s bounds.

To help homeowners understand their obligation when it comes to protecting sewer pipes on their property, this guide explains everything you need to know about building over sewer pipes in the UK, so your project can proceed as planned.

What do I Need to Look Out for When Building Over Pipes, Sewers, and Manholes?

During the planning stages of your project, you will need to establish what drainage pipework exists within your property’s boundary. This can include:

  • Sewer pipes: These carry wastewater from two or more homes and can be found underneath your property.
  • Lateral drains: These carry wastewater from a single home and eventually meet the public sewer network outside that home’s boundary.

If you aren’t sure where the drains beneath your home are, a CCTV drain survey is often the best way to find them. This way, you’ll know where you can easily build, and where it will be more difficult, helping you to plan your project without disturbing the existing infrastructure.

According to Thames Water, you will need to apply for a Build Over agreement if you are planning a building which is within three metres of a public sewer pipe or is within one metre of the point where a pipe on your property becomes a public lateral drain.

Additionally, if you’re planning to build near a domestic sewer with a diameter of 160mm or less, you may be able to apply for a self-certified build-over agreement. The work may be authorised if you are able to confirm your plans pose little risk to the integrity of the pipe.

What Can Happen if my Extension is Built Over a Sewer, Drain Cover, or Manhole Without Permission?

Build Over agreements are a seal of approval from your local water authority for building work you’re planning over or near a sewer they own.

As your local water authority is responsible for all public sewers and public lateral

drains in their region, they will need to be fully confident that your building works do not affect their ability to maintain, repair, and access their pipes.

Without obtaining authorisation from your local water authority, your local council’s building control department may not sign off on your extension’s building regulations compliance certificate, meaning you may experience difficulties selling your property in the future.

Your local water authority also has legal powers under Sections 159 to 171 of the Water Industry Act 1991 to seek an injunction to remove a building obstructing access to the affected pipes and recover the damages.

Can I Bridge Over a Sewer Pipe?

There may be instances where pre-existing pipes may clash with the positioning of the foundation of a proposed building, therefore rendering it impossible to build without affecting the pipe.

An example where this can happen is when a sewer pipe which runs from the back of the property runs over the intended line of the proposed extension’s concrete foundation.

Foundations must never be built over the length of a pipe and, if you intend to build parallel to the direction of the pipe in question, the foundations must lie on one side of the pipe.

If you are building the foundation for an extension at an angle to a sewer pipe on your property, you can put concrete on either side of the pipe and bridge over it. This is one of the most common ways to bridge a sewer pipe.

What Could Happen if I Build Over a Drain?

If you build over an existing sewer pipe or drain, damage could be caused which may result in leaking or blocked pipes. As a result, health problems, foul odours, and environmental damage may occur, resulting in an expensive and time-consuming repair job to solve the issue caused by the building works.

We highly recommend avoiding undertaking any work which could make it more difficult for your local water authority to access and maintain sewer pipes on or near your property.

Get in Touch with Coastal Drains for Advice

Our team of drainage experts have years of experience in their field. They are always fully up-to-date on the latest and current legislation which affects drainage, sewage, plumbing, and building regulations.

For expert support from drainage professionals on any matters related to a construction project on your property, get in touch with our team.