Build over a sewer

Are you considering building a new property – or extending or renovating an existing one? We’re sure you’re excited and possibly a little daunted too. To help your project be a success, we explain why considering any nearby sewers is important at this stage, how to apply for any permission you need and what happens next.

Building an extension can impact the public sewer network serving you and your neighbours’ properties. That’s why you’ll need to submit a build over application if you’re planning to build within three metres of a public sewer.

You may wonder why you need permission, especially if the sewer’s within your land.

Please note you are not permitted to build a new property within 3 meters of an existing public sewer or water mains. Please refer to the sewer diversion and water main diversion for further guidance.


Here are a few crucial reasons you need our permission first:

  • It helps to prevent damage to the sewer – Unless the sewers are considered, they could collapse under the weight of any new structures. This could damage your property, interrupt drainage for other properties and increased the likelihood of flooding. The sewer would have to be repaired immediately, even if the structure had to be demolished first. Reviewing your application allows us to check the necessary precautions are in place early on.
  • We need constant access to our network – We’ll check your plans will continue to allow us 24-hour access to all public sewers and manholes to carry out routine inspections, maintenance, and repairs, which are essential to help us protect your home and our pipes.
  • You’ll have the correct paperwork – Before a building control surveyor will give you a completion certificate or ‘sign off’ your works, they’ll expect to see our permission for the build over/near taking place. If you sell your property in the future, the buyer’s solicitor may ask for a copy of the Build Over Agreement showing our permission for the building works too. Without this, selling your property could become more complicated.

The good news is – if you’re aware of the guidance early on – you can plan your building works with the sewer pipe included early in the design process. Our Build Over a Sewer Guidance Notes explain what you need to consider, including how to determine whether you need to make an application, helpful diagrams, and answers to frequently asked questions.

Because each application and design proposal we receive is unique, approval is given on a case-by-case basis. But we’re here to give you the guidance and support you need to progress your application.

Build Over Applications

Below is a guide on what you need to do when making an application to build over or near our sewers, including links to make an application via our GetConnected portal.


Before you make an application it’s important to take account of the following points:

Are you covered by Building Control?

If you are constructing a new building, the first thing is to check if it is subject to the Building Regulations. If it is then you are required to confirm it meets the standards set out in section H4 of the Building Regulations and this can be assessed by a Local Authority Building Control (LABC) department or an independent approved inspector as per your choice.

If compliant with H4 of the Building Regulations then inspectors at LABCs may approve potential build overs on our behalf, however they would need to do so in consultation with ourselves.

If your proposed extension/building is not subject to Building Regulations, or you are not in a protocol area the following guidance will help you to choose and complete the right application for your needs.

Stage 1 – Make a Build Over Application

Once you have read through the guidance notes and if Building Control approval is not an option for you, then you can make a Build Over/Near application by applying via our portal.

Once your application has been made, our team will review the information submitted and we will respond within 5 days to confirm the documentation is complete or ask for more information if required.

As you apply, we’ll ask some questions to determine if you can self-certify through a ‘Build Over Declaration’. If so, we’ll provide consent to build over our assets within 10 working days and stage 2 and 3 below will not be required.

If the proposals do not meet the Build Over Declaration self-certification points, we’ll automatically transfer you to an approved Build Over application where our team will technically review your proposals. There will be an additional fee for this that you will need to pay.

Our team will technically review your proposals to understand how they might affect the sewer. We’ll arrange a CCTV survey which will trace the line of the sewer and show the condition of the pipe.

You will need to include the following with your application:

  • An existing and proposed site plan (.pdf) (1:100 or larger clearly showing the location of sewers and manholes).
  • A site location plan (.pdf) (1:1250 or larger).
  • A cross section foundation design (.pdf) (1:100 or larger).
  • Copies of all drawings submitted for building regulations approval.
  • An application fee. The initial Declaration of Works fee of £102.00 (incl. 20% VAT) and if required, an application fee for a Build Over of £720.00 (incl. 20% VAT).

Alongside our in-depth guidance notes, please also refer to our Build Over a Sewer Quick Reference Guide.

Stage 2 – CCTV Survey

As part of the process to determine the condition and actual location of the affected sewer, we will need to carry out a CCTV survey. Our CCTV contractor InSewer will be in contact with you to arrange a mutually convenient time to visit your site and carry this out. In some circumstances we will also arrange a site visit by a clerk of works if required.

Where a satisfactory CCTV survey has been provided with your application, or if it was not required, we will arrange a refund for the cost we would have incurred had the CCTV survey proceeded.

Stage 3 – Receive our Response

We will send you our response, setting out any conditions required to be followed for your proposals, within 8 working days after we receive the CCTV survey report for your property. For most properties, this happens within 20 working days from when we received a complete application.

For some sites we may also ask you to complete a Sewer Protection Agreement with us to ensure the protection and future maintenance and access of the sewer. For example, if you were planning to build boundary to boundary of your site. However we will make this clear in our response if this is the case.

Sewer Protection Agreements

Depending on the circumstances of your site, we may ask you in our response to complete a Sewer Protection Agreement (SPA) with us so we can ensure the protection of the public sewer and our future maintenance access.

A SPA is a legal agreement between us - Southern Water - and the property owner to protect the public sewer that is being built over. If the below criteria apply to your plans, then a SPA will be required:

  • Covering 8 metres or more of a public sewer.
  • If the proposal spans from boundary to boundary of your property.
  • Unconventional construction that is not compliant with our Guidance Notes.
  • Impedes access to maintain the public apparatus.
  • If the proposal covers two or more sewers.

The Protection Agreement is required because we as a Water Company have a legal obligation to service and maintain public sewers in our area of operation. If the above points apply, then the proposed build-over will make it hard for us to access, repair and maintain the sewer (our statutory duties) in the future to ensure it continues serving our customers effectively. The agreement ensures the rights of access to repair and maintain that public sewer in the future at the landowner’s expense.

A SPA is made against the property, not the property owner, so you must disclose the SPA to any potential new owners in the future should the property be sold.

The legal documentation is prepared by our Legal Department and paid for separately. The SPA costs approximately £250 for domestic/residential properties and £400 for commercial properties and should be completed before commencing works on site.

Once the SPA is complete, we will provide you with a confirmation letter to inform that the works on site can be completed in accordance with the terms of the agreement and conditions outlined.

Diverting an existing public sewer

If the affected sewer requires a diversion (relocation not replacement of existing line) you will be required to apply for a sewer diversion.

For minor sewers (if the pipe size is <225mm and the depth of the sewer is <3.0m) you have the option of requesting a small sewer diversion through a Buildover application. In addition to our standard application requirements, you will need to submit the proposed diverted sewer plan around your proposal (i.e. extension) in line with the Design and Construction Guidance.

The Design and Construction Guidance (DCG) is covered under Appendix C of the Sewer Sector Guidance document, which replaced Sewer for Adoption (SFA). The DCG details the new design and construction standards for adoptable foul and surface water systems.

You will also need to provide consent from neighbouring landowners if the diversionary work takes place on their land. For existing applications, you can upload this to us as additional information.

For critical sewers (if the pipe size >225mm or the depth of the sewer is >3.0m) you can undertake this through a Sewer Diversion.

Transfer of Private Sewers

On 1 October 2011, legislation introduced by the government transferred responsibility for private sewers and lateral drains to Southern Water – providing clear ownership and better long-term maintenance for the sewer network. We’d recommend understanding the changes before making an application.

The changes mean property owners are no longer responsible for certain sewer pipes that connect their homes to public sewers. Our Building Over a Public Sewer Guidance Notes includes a depiction of where the responsibility now sits for different sewers.

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