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Your Guide to Getting a Build Over Agreement

Updated: Jan 6, 2023

For many homeowners, a property may not feel fully complete until it has had an extension or a conservatory built on its side, or extending to the front or back. In these cases, this may require building over drains or public sewers in order to achieve the effect you want from your new interior space. However, moving forward with your work will not be fully straightforward, as you may need a build over agreement before you will be allowed to carry out your project.

Below, we have provided some professional information on build over agreements and expert tips you will need to know if you plan on building any sort of extension close to (or over) a public sewer. These are the basics that will help to get you started if you wish to go ahead with your planned proposal.

What is a Build Over Agreement?

A build over agreement is a legal document put in place to protect the public sewer or main drain you are intending to carry out work over, or very close to. It gives assurance to your local water authorities that they will be able to access the pipe if they need to clean or repair it. Having this agreement in place also clearly states these facts to buyers if you ever plan on moving and selling your property, so any future owners will not be caught out if engineers from your water company suddenly arrive outside.

You will need the agreement in place because your local water company is responsible for all of the public sewers in your region. As they are responsible for their maintenance, it’s vitally important that there is no building work restricting their access. Just imagine how awful it could be for you as a homeowner if your new conservatory were to be built over a public sewer, which then burst, and there was no way to access it to carry out repairs!

There is also the worry that the weight of your proposed works could cause the sewer to collapse, which will result in structural damage to your extension, interrupted drainage to your property and to others, and will also cause wastewater to flood outside your home. In order to repair the drain, the only option may be to take down the building.

Consulting with and applying to local water companies in your region is stated as part of the process in the Building Regulations 2010 Part H4. Building inspectors may even ask to see a copy of your build over agreement before they will sign off a Completion Certificate, so you must follow the guidelines set and send off an application before you start building over drains.

What You Need to do Before You Make an Application

There are a few things that will need to be established before you apply for permission to build over an underground drain that is managed by a local water authority:

  • If the nearest public sewer is truly within the vicinity of your proposed works

  • That you understand why your local water company needs to know you are planning on building over drains or sewers, or near to them

  • That you have found out about your local water company’s build over/near to requirements, as these may change depending on where you live

  • That you have made sure your proposals fit the regulations and standard criteria given

How to Make an Application

Every local water company will have its own website, and each should have a section dedicated to applying for permission to build an extension over public sewers. You may also make this application by post.

You must make sure that this is carried out, as you will not be able to obtain the required Building Regulations Completion Certificate otherwise. This signs off your building work as complete and makes it easier for you if you ever plan on selling your property. You must also have permission and consent from your local authority before any work on a conservatory or extension is started over a public sewer, as it may then be difficult to make amendments and could cause delays.

Where You Cannot Build Over

There are some circumstances in which you will be denied permission to build any form of extension directly over a public sewer. These include:

  • If the sewer is pressurised (i.e. a pumping or rising main)

  • If it is a strategic sewer (it carries waste for a large number of properties)

  • If an entirely new building or dwelling has been proposed

  • If any manhole covers, drain covers or inspection chambers will be located inside a building because of the work

In the event of a completely new property being built, your local water authority will most likely advise that the sewer is diverted instead. If this is the case, you will need to get in touch with a professional drainage firm that also operates as a contractor, in order to have the moving work carried out.

Your local water company will not allow manholes or drain covers to remain in the interior of your property, because of the increased risk of flooding and issues with odour. As such, both must be removed entirely, and piped through manholes should be reconstructed outside of the extension work.

When You Will Not Need an Agreement

Whether you will need an application or not depends on how close to your property boundary (and to the public sewer) you are planning on building. This may vary depending on the region you live in, but the general guideline will usually be that you need permission if your planned work falls within 3m of the nearest public sewer.

If all the sewers on your property are your responsibility (i.e. they are private sewers), then you will not require a planning agreement, though you may still require planning permission for certain extensions.

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