Build over or near to a public sewer

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 is within your land.

Here are a few crucial reasons you need our permission:

• 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 increase the likelihood of flooding. Reviewing your application allows us to check the necessary precautions are in place early on and ensure the sewer is in good structural condition before you impede future repair access.
• 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 need 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. The information below will 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.

Before you apply

Cases when you will not need a build over or near application

1. If you are constructing a new extension, first you should check if it is subject to the Building Regulations. If it is, then you are required to confirm that 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.
   
   Some LABCs or inspectors may be able to progress your proposals in consultation with us, rather than submitting a build over application to us.
   
   You can use this route, if your development meets all the following points:
   • Pipe size is 225mm or less
   • Pipe depth is less than 3m
   • The total length of the public sewer built over is less than 6m
   • Access to the public sewer is unimpeded and you’re not building boundary to boundary (within 1m of property line).
   • It’s an extension not a new detached structure
   • Building over/near only one public sewer
   
   If your proposal meets all the above requirements, then you may be able to progress with your works through Local Authority Building Control (LABC). Alternatively, you can apply for a Build Over Self-Declaration with us.
   
   
2. If you are building or undertaking changes to a non-residential building over or near a public sewer then you may be required to request a sewer diversion. If you are unsure, please contact us for advice.

Building proposals that we do not accept

There are situations where we never allow the building over or near to of our sewers. These include:

• Building over or near to public water mains, pumped or rising mains, vacuum mains and strategic or ‘trunk’ sewers
• Building over or near to existing sewers on new development sites or re-development sites. Instead, you can look to divert the sewer, or to save cost, modify your plans so that your building is at least 3 metres from the sewer
• Where there would be an internal manhole or change in pipe direction (i.e. Y-connection or a junction of a public sewer) within the proposed building. These are not allowed due to potential odour and flooding issues. We will need to have access to the sewer. You’ll need to relocate these outside the property to get approval
• If there are easements or restrictive covenants on the pipework by your proposed works, you won’t be allowed to build near or over the pipework
• The pad, raft and cantilever foundation types over the public sewer are not permitted as it can impact our future access to repair the adjacent public sewer and significantly increase the risk of damage to the structure during repair works. We also do not permit reinforced concrete floor slabs over public sewers for the same reason
• If you have Boundary-to-Boundary infill structure, where there are already structures both sides of boundary impeding future maintenance and repair access to the public sewer
  

Build over or near to a sewer application routes

When you apply to us there are two routes your application can take depending on your design:

• Build Over Self-Declaration
• Build Over Formal Approval Application (with/without Sewer Protection Agreement)

The two applications differ in costs and follow different process. The quick reference guide is designed to help you understand what route your application will take with reference to certain circumstances. It details whether it will be a Build Over Self-Declaration, an approved Build Over Formal Approval Application, an approved build over with a sewer protection agreement, or where the building project proposal won’t be acceptable.

Download the Build Over or Near a Public Sewer Quick Reference Guide

In some cases, we may decide to turn your Build Over Self-Declaration into a Build Over Formal Approval Application, upon review where additional cost will be required.

Locating the sewer around your property

Before starting any construction works, you will need to locate any public sewers to confirm whether you are building within 3 metres. Once any sewers are located you will need to determine the sewer ownership, identify the sewer size, depth, and pipe material.

You can request an indicative sewer or water map online, that will help with your investigation.

Due to recent changes in legislation, our maps may not always show all public sewers. If available, we only hold records for public assets, so any private pipework will not be shown. If there are no sewers showed on the map around your property, you will need to arrange a CCTV survey or careful excavation. Alternatively, you can apply for a Build Over Formal Approval Application, and we will do all necessary investigation for you.

What are the signs of a sewer in your property?

We started construction works and we’ve now found a sewer, what should I do?

Which sewers are a responsibility of Southern Water?

Here are more details on what you will need and how it all works for each application route.

Utility Crossings

If you are installing a new utility cable, pipe, or duct such as a high voltage electrical cable that will need to cross a public sewer you will need to submit a buildover/close-to application. This application will require a CCTV survey with sonde location to confirm the exact position and depth of the sewer you are proposing to cross.

For more information about Utility Crossing & Locations, see our technical guide.

Making an application

Build Over Self-Declaration

Building over one public sewer, where the total length of sewer built over is less than 6m, the sewer to be built over is a non-critical public sewer with an internal diameter of 225mm or less, sewer is less than 3m deep, and not a boundary-to-boundary extension, then it’s likely it can be progressed under a self-certified build over approval known as a Build Over Self-Declaration. As part of the application process, we ask all applicants to complete a list of questions to determine if you meet criteria.

Steps we'll take to help with your project

Don't worry we'll be in touch along the way to make sure everything goes smoothly.

Build over or near a sewer Formal Approval Application

If your application answers do not meet the Build Over Self-Declaration criteria, your application will automatically progress to a Build Over Formal Approval Application.

We’ll technically assess your proposal to determine that it adequately protects the public sewer and our future access to maintain it. We’ll suggest any changes or conditions that will need to be made to assist you in progressing your application to the approval stage (if required).

It is possible that you have applied for a Build Over Self-Declaration, however upon review we found that it does not meet the Self-Declaration criteria. In this case, we will switch your application to the Build over Agreement application. You won’t need to reapply, but you will need to make payment using BACS or a card payment over the phone to cover the additional fee for the application and CCTV survey (if applicable).

For some sites we may also ask you to complete a Sewer Protection Agreement (SPA) with us to ensure the protection of access for any future maintenance and repairs of the stretch of sewer being built over. This will be clearly identified in our conditional approval letter and the reason it is required.

Steps we'll take to help with your project

Don't worry we'll be in touch along the way to make sure everything goes smoothly.

Apply Now

Still have questions? We are here to help

We understand that all projects are different, and it might be hard to understand what the right and most cost-effective option is. Please visit our Frequently Asked Questions page for more guidance or simply request a call back from our helpful team. 

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