Building over or near to sewers
If you're planning to build an extension, conservatory or other structure over, or within three metres of, a public sewer or lateral drain, you'll need to let us know before work starts. This helps us protect both your property and our network, now and in the future.
Before you start
At the planning stage, it's important to check whether there are any water mains, public sewers or lateral drains within your land or close to your proposed build.
Understanding what's underground before work begins can help you:
- Design your project correctly from the outset
- Avoid delays during the application process
- Reduce the risk of additional costs or changes later on
When building over a sewer may not be possible
In some circumstances, we may not be able to approve a build-over proposal.
This is usually the case where:
- The sewer has an internal diameter greater than 225mm, or
- The sewer is more than three metres deep
If this applies to your property, you may need to build further away from the sewer. If you're unsure, please contact us and we'll be happy to discuss the options available to you.
Commercial buildings and detached structures
If you're planning to extend a commercial property or build a new detached structure, you may need to divert the sewer rather than build over it. You can find out more about sewer diversions on our website.
Building near water mains or pressurised sewers
For safety and operational reasons, we do not allow structures to be built over, or too close to, water mains or pressurised sewers.
If you discover one on your site, please contact us on 0800 917 2652 so we can discuss the best way forward.
You can also find out more about water main diversions on our website.
Which application do I need?
We offer two types of build-over application:
Self-certification
A quicker option for simpler projects that meet specific criteria. If your proposal qualifies, you can complete a self-certification application and receive confirmation from us once it has been reviewed.
Full application
A more detailed application for higher-risk or more complex projects. This involves a technical assessment by our specialist team to ensure your proposal protects both your property and our assets.
How do I know which one is right for me?
Before applying, you'll need to know:
- The location of the sewer
- The depth of the pipe
- The pipe material
- The internal diameter
Our guidance notes explain the requirements for each application type and what we can and cannot approve.
If your proposal meets the self-certification criteria, you'll be able to follow that route. If it doesn't, you'll need to submit a full application.
What does it cost?
The cost depends on the type of consent required:
- Letter of consent with no changes to our network: £278.10
- Letter of consent following alterations to our network: £936.85
- Legal agreement: £1,053.00
These charges cover the administration of your application, technical assessment and support, any site inspections where required, liaison with Building Control or your approved inspector, and issuing your consent documentation.
You can view all current charges in our Schedule of Charges.
Before you begin
A sewer trace is strongly recommended before any excavation, or construction work takes place.
Please remember that you must not start work until we have approved your application.
If you're still unsure which application is right for your project, we recommend speaking with your builder, architect or design team, who will be able to help you understand the requirements and prepare your application.
Are you a customer in need of extra support?
If you’re converting or extending your property to make it more accessible for someone with physical impairments, then let us know on the ‘nature of proposal’ section of your application form. We can offer additional support such as helping you to fill in your application, and more advice and support through the building and construction process. To discuss your proposals please contact our dedicated Build Over Sewers team on 0800 917 2652.
Available applications
Self Certification
A shorter process where you can 'self-certify' as long as you meet certain criteria in regard to how your work will protect our sewer.
Full application
A more detailed process, needed for more complicated or higher risk work, that involves a technical assessment of your proposals by our dedicated team.