Build over or near to a public sewer FAQs

Build near - is where you are building within 3 metres of a public sewer, but not over it. Build-over - is where you are building within 3 metres of a public sewer and directly over it. Both need the same application – Build over or near a sewer.

Southern Water has a legal duty to protect and maintain the public sewers. We need to ensure that the sewer is in a good structural condition before it is being built over or close to mitigate any sewer damage risks. Also, 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. Without this, selling your property could become more complicated.

Yes, public sewers can run through private land/property, however it is still responsibility of Southern Water to protect and maintain these sewers. Therefore, any build over or near a sewer works would require application submitted to us, to make us aware and for us to check the condition of the sewers.

If the sewer serves two or more properties or is a lateral drain outside your boundary, then it is likely to be deemed public. There are also uncharted public sewers. Private gravity sewers that were constructed and connected to our network prior to 1st July 2011 are now our responsibility as public sewers under S105a of the Water Industry Act when they were officially transferred on 1st October 2011.

Private gravity sewers that were constructed and connected to our network prior to 1st July 2011 are now our responsibility as public sewers under S105a of the Water Industry Act when they were officially transferred on 1st October 2011. Providing clear ownership and better long-term maintenance for the sewer network. Lateral drains (which is a pipe that serves only one property) continued to be privately owned and maintained up to the property boundary, from which it then becomes a public lateral drain.

As a result of the transfer, the number of sewers we are responsible for has increased by approximately 19,000 km. Many of the transferring sewers had not been mapped and so their location and condition are unknown and won’t be shown on our mapping records.

Due to the absence of this detailed information about the transferred sewers it must be presumed that they will be present within gardens and in land to be developed and are therefore likely be affected by any building proposals.

We’ll need you to help identify any sewers near your build during your application. You should assume that any sewerage that is located on your land or discovered during your work is public apparatus and, in our ownership, unless it can be shown to be otherwise. If your property and associated sewer was laid after 1st July 2011 it would be assumed private unless formally adopted by us as Southern Water.

This can often happen due to the transfer of private sewers in 2011, which meant that many smaller sewers came into our ownership but weren’t mapped on our systems. We’ll appreciate your help in identifying sewers on your land and we can help determine if they are public or not. Please get in touch with our team if you found public sewer which has not been mapped.

If there isn’t an obvious public sewer crossing your site according to the sewer map, check if there are any manholes on site or any drainage details in your property’s legal documentation.

If you found drains and manholes or there is mentioning in your documentation, we strongly recommend carrying out a detailed investigation involving CCTV or careful excavation before you start your building works.

If you find a sewer after you started construction works and it’s within 3 metres of your works, you will need to stop the building works immediately and make a Build Over Application to us. If you are unsure and need an advise, please get in touch with our team.

We measure the 3 metres from the outside face of the sewer pipe or manhole chamber (whichever is closest to your proposed building) to the outside face of your foundations.

When it’s not clear if you are or aren’t within 3 metres of the sewer throughout its entire length, then you can ask your architect or builder to help. Alternatively, you can arrange your own CCTV survey to determine the sewer location.

Yes, a build-close-to application will still be required to ensure there is no additional loading on the sewer and to ensure the structure and its foundations would not be affected should we need to open-cut repair the public sewer in future.

No, it’s important you do not start any construction works until you have our approval. We may ask for some amendments or conditions to be put in place, and you’ll need to consider your options before any construction work begins.

As soon as you have our written letter of conditional approval or that of Building Control’s, you’ll be able to begin construction works. However, if we ask you to complete a Sewer Protection Agreement, you can’t begin construction until this is completed.

This is more common than you think, you will need to stop your building works and contact us on 0330 303 0119 where we will give you guidance on the build over/close to process.

Even if you’re exempt from Building Regulations, and planning a constructions works over  or close to Southern Water sewer, you will still need our approval, so we can ensure sewer protection and access.

No, if Building Control have consulted with us and we have provided a Conditional Approval response, you will not need to apply with us.

If you want to identify if a sewer runs through your property, it’s location (often through back gardens in towns), locations of connections and direction of flow, you can often do so with some simple investigative work with the below tips.

• Check your legal documentation relating to your property, it may include details of drainage arrangements and plans.
• Your architect or builder maybe able to help you to find out if there’s a public sewer or drain within your property. Or employ a specialist drainage company to help.
• Look for manholes in and around your property and ask neighbours if they have any on their land. Visually trace a potential line of the sewer from these manholes and cautiously dig a trial hole to locate the pipe.
• Run your tap or flush drain tracing dye down your toilet and have a look with a torch down a manhole to work out the direction of flow and where your property connects to the sewer.

If you’re going to lift a manhole cover, be careful as they may be heavy, and you may need help. If another sewer line branches onto it then it is most likely a public sewer. You may be able to visually determine information that can be added to your drawings.

Left:Examples of manhole/inspection covers you may find.
Right: Pipes forming a junction suggests your property may be part of a shared run with other properties.

For minor sewers (if the pipe size is <225mm and the depth of the sewer is <3.0m) you can include a minor sewer diversion (i.e. less than 3 manholes and are within your property boundary of the sewer) through a formal Build over application.  This cannot be progressed under a self-declaration application because you are realigning the sewer pipework. In this case you will need to submit the proposed diverted sewer plan around your proposal (i.e. extension) in line with the Design and Construction Guidance in addition to our standard application requirements mentioned above. If it extends to the neighbouring land, you will need to obtain their formal permission.

The Design and Construction Guidance (DCG) is covered under Appendix C of the Sewer Sector Guidance document, which replaced Sewer for Adoption (SFA). The DCG details the new design and construction standards for adoptable foul and surface water systems.

For critical sewers (if the pipe size >225mm or the depth of the sewer is >3.0m) you can undertake this through a S185 Sewer Diversion application. If the affected sewer requires a diversion (relocation not replacement of existing line) you will be required to apply for a sewer diversion.

You will need to obtain consent from neighbouring landowners if the diversionary work takes place on their land. For existing applications, you can upload this to us as additional information.

There are situations where we never allow the building over/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. 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 propose to carry out an in-fill extension (boundary-to-boundary) when both neighbours either side have already built over the public sewer and there is no alternative sewer access, then you may not be able to progress with the build over application.  You may need to reduce your extension layout and submit a revised layout.

No, pressurised sewer mains are critical assets and pose risks. It would cause a substantial damage if they were to burst. We don’t allow building over the water mains and pressurised sewer mains.  Please see a water main diversion or sewer main diversion and the required standoff distances.

Where constructing the new structure within 3m of the public sewer, the foundations must extend to a depth of at least 150mm below the invert (inside base of the pipe) of the sewer.

No, new detached/semi-detached properties/new structures on a development site are not allowed to build over the public sewer. You’ll need to modify your plans to achieve the 3 metres stand-off, or a sewer diversion will be required instead.

No. If you are using the existing building’s foundation, there is no additional loading onto the public sewer and no new foundations within 3m of the sewer is being built, we won’t need an application if. You should contact building control to ensure the existing foundations are suitable for your new construction.

As a general tip, if your foundations are 150mm below the public sewer invert, there shouldn’t be any additional loading on the sewer. If you are unsure and need an advise, please get in touch with our team.

If the manholes chamber is not a change of direction chamber, you should be able to relocate it outside of the property, maintaining a minimum of 500mm distance from their outer edge of the footings to the chamber.

We don’t allow internal manholes or building over the changes of pipe direction. This includes doubled sealed covers because it makes it difficult for us to maintain the sewer. This increases the risk of flooding, odour, rodent issues, and difficulty clearing blockages within your property. Internal manholes will need to be relocated outside the property.

The affected length of sewer will have to be removed and replaced with new pipework. It will be explained in our conditional approval letter. You’ll need to employ your own builders to carry out this work.

If you are proposing to use piled foundations, then an approved build over application will be required. The usual 500mm horizontal standoff distance increases to at least 1m, and a post-piling CCTV survey will also be required at your expense.

The excavation must be 150mm deeper than the sewer invert level because any relayed or replaced public sewer pipework requires a minimum of 150mm compacted granular bedding and surround to the pipework. Therefore, the minimum excavation depth to replace or repair the sewer will be 150mm below the invert of the sewer. It also ensures that there is no loading onto our sewer.

If you are demolishing your old structure and building a new one (re-development), we would class this as a new detached/semi-detached structure.  Therefore, we won’t allow this to be built over the sewer. You would need to revise the design so that the new structure and footings are not closer than 3m of the sewer or look to undertake a sewer diversion whilst ensuring that any associated change-of-direction manholes are no closer than 500mm from the new footings/walls. We may permit a build-close-to application in some circumstances on a case-by case basis. Please get in touch with our team.

No, we do not allow to build over critical sewers. You will need to change your building plans.

An easement is a legal right to ensure a defined stand-off distance is maintained from a length of pipe to provide adequate access for future repairs. 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.

If you are not digging any new foundation and no additional loading is being placed on the public sewer, it may be classed as a temporary building (assuming it could easily be emptied and demounted at short notice i.e. a small shed), then you would not need to apply for a build over application. However, please be aware we need 24/7 access to maintain and repair our sewers.  So, any temporary structures within the stand-off zone or over the sewer may need to be taken down at short notice and at your expense.  Therefore, you should try to avoid building any temporary structures over or close to the sewer.

Non-reinforced paved areas would not need an application provided they did not impede access to open-cut repair the sewer in future.  However, specialist surfaces such as large areas of continuous artificial grass area should be avoided, as these would make it difficult to open-cut repair and reinstate the public sewer in future.  Southern Water would not be liable for any additional repair costs for damages or replacement to these types of surfaces if they are laid over/close-to the public sewer stand-off area.  You would not need to submit an application if you are replacing an existing structure using existing foundations i.e. like-for-like with no additional loading and subject to Building Control approval to use existing foundations.

For rising mains, we normally require an additional 1 metre stand-off compared to gravity sewers depending on depth. Please also review the guidance for locating rising mains.

We’ll only provide you with a self-certified Declaration approval if you meet all our consent criteria.

Consent Criteria

• Your development involves a single or double storey residential extension, conservatory, annexe or garage which is attached to the existing property.
• You are not aware of any historic blockages, flooding, odour or other operational issues with the public sewer or public lateral in the last 12 months.
•  There are no easements or restrictive covenants which relate to the pipework.
• The public sewer/public lateral is gravity- based foul, storm water or combined flow from domestic properties, flows freely and is not pressurised.
• The depth of the pipe from the existing ground level to the pipe channel (invert) is less than 3 metres.
• The diameter of the sewer/drain is 225mm or less.
• The proposed structure/foundations will have a minimum of 500mm horizontal clearance of any public access point (manhole, inspection chamber or rodding eye). If the proposed structure is to be built over an existing access point, this may be resolved by relocating it to a new external chamber or if the shape of the proposed build/extension is adjusted to meet this requirement.
• The development proposals will utilise strip or trench fill foundations.
• The pipe material is clay, concrete or ductile iron. If it’s pitch fibre, brick, asbestos cement, or plastic it can potentially be resolved if the pipework is replaced with new vitrified clay or ductile iron before building begins.
• The development proposals will utilise strip or trench fill foundations.
• Your foundations are designed to be at least 150mm below the pipe invert when located within 3m (horizontally) of the public sewer.

If the proposal is to build over the sewer, the following points are also applicable:

• The sewer pipe being built over is in a good condition - established by either exposing the length of pipe being built over/near for a visual inspection by our Adoption Manager, or through an internal CCTV survey with sonde location equipment. Poor pipe condition can be resolved if the defective pipe is replaced at your expense.
• Excluding where the sewer may pass through a load bearing wall, 500mm horizontal clearance will be achieved between the edge of the new foundations, walls or ground beams and the public sewer.
• There is no change in diameter, direction, material, or gradient inside the area of the proposed structure - Minor inconsistency (excluding changes to sewer layout) can potentially be resolved by carrying out agreed minor amendments before building, i.e. relocating a manhole chamber to an external location.
• You do not intend to build across the full width of your garden (a minimum width of 1m will be required between the boundary and the proposed extension).
• Total coverage of the sewer is less than 6 metres (including pipework already built over).
• Your design incorporates a minimum of 300mm headroom between the underside of the new floor slab and the crown of the pipe.
• If the public sewer/public lateral passes through a load-bearing wall, the foundation design complies with H4 Building Regulations standards and our design criteria.

That’s fine, complete as much of it as you can in your application, when you answer ‘no’ to some questions or can’t fully complete it, we’ll likely transfer your application to a formal build over application, where our team can review your proposal in detail.

Yes, it’ll need to be to a good quality, dated within 6 months, include a detailed (.pdf) report, use SONDE location, provide site photos and a supporting plan showing sewer dimensions, layout of manholes and position of sewers, and be submitted to us when you make your application. For where this is the case, we will refund the part of the application fee it would have cost us to carry out our own survey.

Download an Example of CCTV plan

If a blockage was identified during the CCTV process by your private contractor, you will need to contact Southern Water operational team on 0330 303 0368 to arrange for this to be cleared. If the survey is undertaken by us, then we will make these arrangements for you.

We aim to complete CCTV Surveys within 20 days, however, we understand there are instances where these timeframes won’t be suitable for you. If this is the case, your alternative option is to contact another drainage service company that can carry out the CCTV survey for you.

Southern Water accept CCTV surveys that have been carried out by other companies, however, please bear in mind that the company must have SONDE location technology capability for it to be sufficient for your Build over Agreement application. The survey must be dated no more than six months prior to being provided to Southern Water and they must provide a plan showing dimensions i.e. sewer depth, pipe sizes and position relative to the existing property etc.

If you opt to contact another drainage service company, please follow these steps:

• Please notify us via the GetConnected customer dashboard so that we can stop the instruction with InSewer/Dyno.
• Ask your contractor to complete our Southern Water H&S 460 form “Safety Instructions to Contractors”, which will need to be returned to us and approved before contractors can enter into or work on public sewer apparatus.
• Please refer to the accompanying example CCTV survey report to find all the information we require from your own CCTV survey, including a sewer plan drawing. We may not be able to assess and approve your CCTV report if it does not require all the necessary details.
• Once the survey is complete, please send the PDF report to us via the GetConnected customer dashboard so that our technical team can complete their assessment. If it is an acceptable survey your application can progress and we would refund you £200, which is the cost of the CCTV survey with InSewer that will no longer be required.

We may permit a Build over application to be progress without a CCTV survey if there are no other public sewers crossing the site and where the public sewer pipework is being replaced with new pipework.  Please note, that any existing plastic pipework needs to be replaced with new vitrified clay material pipework when building over sewers.

When we receive your application, we check that we have all the correct documentation to progress. If we don’t, we’ll ask you for this further information

Some common reasons we ask for further information are due to:

• An incomplete application
• No site location plan(.pdf)(1:1250orlarger) submitted.
• No detailed drawings(.pdf) of the foundation design and details.
• No existing or proposed plans(.pdf) submitted including existing drainage requirements.

Some common reasons we can’t provide approval are due to:

• There is a change in direction, change in material, change in diameter of pipe work under the proposed building.
• Any change in the material of the pipes under the extension.
• Your foundations are not taken down at least 150mm below the invert of the sewer.
• It’s a new detached building within 3m of the sewer.
• Redevelopment work within a required easement.
• You are building over or near critical sewers.
• You are using unconventional foundation construction.

Don’t worry, our response letter will include detailed reasons why we couldn’t give an approval for this proposal. If you can change your proposal as per our feedback and guidance, please upload your revised design to your portal application for us to review.

A Build over formal approval application fee of £720 includes:

• The technical review, administration work including agreeing any changes and an inspection by the Adoption Managers (when required)
• A CCTV survey carried out by a company called InSewer (£200)

If a CCTV survey shows structural defects in the sewer i.e. fractures and the defects in themselves aren't causing any operational issues in our sewer network, then Southern Water would not be required to replace that section of sewer until it deteriorated and causes operational issues.  However, should you wish to build over this public sewer and impede our future access to repair it, then you would be required to undertake the replacement of defective pipework to ensure the sewer is in good structural condition before starting your building works, which will also give you peace of mind it is a new sewer.

Depending on the circumstances of your site, we may ask you in our conditional approval letter to complete a Sewer Protection Agreement (SPA) with us so we can ensure the protection of the public sewer and our future maintenance access.

A SPA is a legal agreement between us - Southern Water - and the property owner to protect the public sewer that is being built over.

If the below criteria apply to your plans, then a Sewer Protection Agreement will be required:

• Covering 8 metres or more of a public sewer.
• If the proposal spans from boundary to boundary of your property (ie there must be a gap of 1m from the boundary to the new foundations on at least one side of the extension for it not to be deemed a boundary to boundary extension).
• Unconventional construction that is not compliant with our Guidance Notes.
• Impedes access to maintain the public apparatus.
• If the proposal covers two or more sewers.

The Protection Agreement is required because we, as a Water Company, have a legal obligation to service and maintain public sewers in our area of operation. If the above points apply, then the proposed build-over will make it hard for us to access, repair and maintain the sewer (our statutory duties) in the future to ensure it continues serving our customers effectively. The agreement ensures the rights of access to repair and maintain that public sewer in the future at the landowner’s expense.

A SPA is made against the property, not the property owner, so you must disclose the SPA to any potential new owners in the future should the property be sold.

Once the agreement is ready you will be asked to sign this agreement before commencing works on site. The whole process of paying, drafting, and signing the Sewer Protection Agreement may take a month or more.

Once the Sewer Protection Agreement is progressed by our legal team, they will advise you. If an SPA is required, it will be Condition 1 in the approval letter.  Works should not commence on site until the legal SPA is signed.

If a Sewer Protection Agreement is required, details of the required drawings and proof of ownership will be included in the Conditional Approval response letter.  What we need for Sewer Protection Agreement is:

1. An electronic copy (PDF format) of the comprehensive drawing to incorporate the items details above, indicating the length of sewer that is being impeded by the works and being built over; marked “A-B” and coloured red. The perimeter of the site should be coloured green
2. A copy of the location plan at 1:1250 scale (PDF format). The perimeter of the site should be coloured green.
3. The name and address of your solicitors if you wish to be represented by a solicitor. If you want to represent yourself, please confirm.
4. Proof of ownership. This should be in the form of up to date:
   - Official Copy of Title Register Entries
   - Title Plan relating to your property.

    

   If you do not have a copy that is dated within the last 6 months, then please check the Land registry and search property ownership information. The Title plan can be found on the same page of the land registry website as the title deed – it is available in a link directly under where the title deed / copy of ownership register is found.

5. Building Regulation Number (if applicable).

The Sewer Protection Agreement will be sent to you by our legal team using DocuSign.

Our Legal Team will prepare an agreement document for you and will ask you to pay a fee to them directly. The Sewer Protection Agreement legal fee is approximately £250 for domestic/residential properties and £400 for commercial properties.

If your building proposal has changed after you have made a Build Over Application, then you will need to make us aware, and we will need to do another round of review and potentially change approval and SPA at additional cost. It is recommended to do a detailed site investigation and firm up all construction plans before making an application.