A build over agreement is an agreement between you as the property owner and your local water company that you arrange with the water company if you’re building within 3 metres of a public sewer or 1 metre of a public lateral drain. (A public lateral drain is a drain that connects your private pipes to the public sewer pipe.)

“Build over” is therefore a bit of a misnomer because the agreement is not only required when you are actually building over a public pipe but potentially also if just building near it. 

In the domestic residential context, build over agreements tend to be relevant most often in relation to undertaking an extension. 

The purpose of local water companies requiring such agreements is to ensure that public pipes are protected and remain accessible. 

Without a build over agreement, you may not be granted a Building Regulations completion certificate, which you’ll see from our Building Regulations page could be a rather big problem, and/or your water company could seek an injunction to remove the building and potentially recover damages. 

Your local water company may require you to adjust your plans so the time to focus on whether or not you need a build over agreement is during the design planning stage. 

The earlier the better for working out if you’re likely to need one or not. To actually make the application though, you’ll need drawings so you won’t be able to apply until you have those and any other required documentation.  

The process of dealing with build over agreements is thankfully usually very straightforward.

The first step is to find out where the pipes are. 

Maybe you’ll have received a drainage and water report from your solicitor when you bought your property and that contains a map showing the public pipes. If not, you should be able to get a report directly from your local water authority or a utilities search company. 

Here, for example, is the page to obtain one from Thames Water. Here is a link to an example Thames Water report so you can see what they look like.

If you’re looking to save money, perhaps it’s worth contacting your local water authority (or at least having a dig around their website) to see if they have a free option for getting the information, such as visiting one of their offices to look at paper copies. Your local council may also have the information you need.

You could alternatively, or additionally, get a drainage CCTV survey done by a drainage company. This may be necessary anyway for planning your building works or if the water company doesn’t hold records of public sewers for your property (before public sewers became the responsibility of the water companies they were private and not necessarily documented so many remain undocumented). 

To do their CCTV survey, the drainage company will need access to the pipes. Usually this is via an inspection chamber or manhole. Look in advance to see if there’s an inspection chamber or manhole located on your property somewhere. An inspection chamber is a dug out area with a cover that can be removed so you can look down and access the pipes. A manhole is basically a larger version that enables a person to actually get into the dug out area. Have a look on Google Images if you’re not sure what they are or what you might be looking for. If there isn’t one on your property, you’ll need to check with neighbours to see if there is one on their land and if the pipes can be accessed that way. In a row of terraced houses, for example, not every house in the row will have them. 

Usually companies will send CCTV videos with a report of one kind or another following their visit. Be clear also about what you’ll need that report to include. For example, you’ll probably at least need the following:

If you’ve found a public sewer or public lateral pipe and you plan to build within 3 metres of the former and/or 1 metre of the latter, whomever is doing the design work for you will likely handle this for you. They’ll probably charge though so if you want to try to save money, you could do it yourself. That’s what we did and it was easy (though if your plans are anything less than straightforward, bear in mind that it may be more cost efficient just to have the professionals handle it).  

If you go the DIY route, your local water company will no doubt have much information available online about this so the first port of call is to Google the name of your local water company and “build over agreement” or otherwise find the relevant pages on their website. Often they can be found under the “developers” section of their website. They’ll have set out instructions there for how to apply, including what documentation you’ll need to submit. If you’re struggling, give them a call. 

You need to check what your own local water company requires.

To take Thames Water as an example:

They offer two options. One is applying for a self-certified build over agreement and, if that isn’t viable, the other is applying for an approved build over agreement. When we did it, the former was free and the latter was £299 if doing it online. At the time of writing the Thames Water website now seems to suggest that it is only £70 if the pipe is less than 150mm diameter internally. 

For self-certification, you have to certify as to various things such as: 

Here is the full list from Thames Water for self-certification.

You can get all of that information from your drainage and water report, CCTV survey and/or your building works designers (i.e. architect) if you don’t already know it. 

You’ll also need certain documentation to apply, such as a site location plan, existing and proposed building and drainage plans and a sectional drawing showing relevant foundations in relation to drainage. To apply with Thames Water and to get further information, you can go here for self-certification or here for approved. The latter also includes some examples of documentation needed which may be helpful.