How Close Can You Build to an Inspection Chamber?
Inspection chambers (manholes) are essential access points for cleaning and camera inspections of drains and sewers. Understanding the regulations surrounding buildings near them is vital for homeowners, contractors, and property developers to ensure they never build too close to them.
In this article, we’ll discuss the guidelines for building near manholes and key considerations to keep in mind to avoid any complications in your construction projects.
Can you build an extension over a drain cover?
Organising construction work on your property is always a significant undertaking. This is not only due to the costs and timescales involved but also because ensuring that every aspect of the project complies with the relevant building regulations is crucial.
No matter what kind of project you are planning – whether you are adding an extension, a conservatory, a new garage or anything else – it is vital to make sure that none of the building work interferes with or damages the underlying pipework and drainage system. This includes ensuring that any nearby inspection chambers, manholes or other access points aren't blocked or obstructed.
Failing to do so can compromise the safety of your project and potentially get you in trouble with your local water authority. It is essential to get up to speed on the relevant regulations before you start building to ensure you aren't too close to an existing drain access point.
What are the rules for building near inspection chambers?
Inspection chambers allow those responsible for the public sewer system to access and survey the sewers and drains, and perform essential maintenance and repair work.
These entry points will be situated at key intersections along the sewer pipe system's length and in areas where the pipe size changes or the pipe direction changes horizontally by more than 30 degrees.
Access points are essential for maintaining the public drainage system, allowing your local utility company or water company to carry out crucial checks of public sewers that serve more than one property. As such, strict rules are in place to ensure they are never blocked off or rendered inaccessible by new building projects.
These rules include:
- The new extension, including inspection chambers, manhole covers and rodding eyes must not cover up access points
- The foundation of the new building must be situated at least 500mm away from the inspection chamber or manhole cover
Suppose your current plans do not meet these criteria. In that case, you will have to either change the shape or position of your new building project to provide the necessary clearance or arrange for the inspection chamber and manhole to be repositioned as part of the construction work.
How to obtain approval when building near an inspection chamber
To ensure that your building project will not interfere with inspection chamber access or the functioning of your drainage system, you may need to apply for a build-over agreement with your local authority or water company before commencing work.
A build-over agreement will be required in the following circumstances:
- If the construction is within 3 metres of a public sewer, defined as a pipe serving more than one property
- If the construction is within 1 metre of the point where a private drain serving only your property crosses your boundary, where it becomes a public lateral drain
The nature of the permission process will also depend on the details of the project itself:
- If you are building over or near a domestic sewer with a diameter of 160mm or less, you can potentially apply for a self-certified build-over agreement, which allows you to apply online for free and confirm that your project meets all of the necessary criteria
- If you are building near a sewer with a larger diameter than this, or if your answers to the self-certification questionnaire do not meet the criteria, you must apply for an approved build-over agreement for a set fee. This will require you to work directly with the water authority to ensure your project meets the required standard
A build-over agreement will be required in the following circumstances:
- If the construction is within 3 metres of a public sewer, defined as a pipe serving more than one property
- If the construction is within 1 metre of the point where a private drain serving only your property crosses your boundary, where it becomes a public lateral drain
The nature of the permission process will also depend on the details of the project itself:
- If you are building over or near a domestic sewer with a diameter of 160mm or less, you can potentially apply for a self-certified build-over agreement, which allows you to apply online for free and confirm that your project meets all of the necessary criteria
- If you are building near a sewer with a larger diameter than this, or if your answers to the self-certification questionnaire do not meet the criteria, you will need to apply for an approved build-over agreement for a set fee. This will require you to work directly with the water authority to ensure your project meets the required standard
Find out more
To learn more about how this process works, read Thames Water's guide,“Building over or near a public sewer“. If you want to learn more about inspection chambers and the regulations regarding access and maintenance, look at our guide to inspection chambers and manholes. If you need practical support and advice regarding inspection chambers, explore our manhole inspection services, which are available for commercial and domestic customers.
You can also call us at 0800 526 488 for more information or fill out our online inquiry form to request a callback.