Building over or near a sewer

A Sewer Protection Agreement allows us to be sure we have continuous access to that stretch of sewer. You will need an inspection and a Sewer Protection Agreement if you are:  

• building over 8m or more (coverage) of the public sewer
• building over two sewers
• if the proposed extension is covering the sewer boundary to boundary (not achieving a minimum of a 1 metre gap of the property line).  

We will let you know if this is needed in our conditional approval letter. 

You will need an inspection if you are making any amendments to the public sewer such as: 

• making a minor division
• relocating/removing a manhole/inspection chamber 
• replacing sewer pipework. 

A CCTV survey should trace the line of the sewer and show the condition of the pipe using sonde track and trace technology. Please see a CCTV survey example.    

If you carry out and provide your own CCTV survey it must be: 

• dated within 6 months 
• include a detailed (.pdf) report and site photos 
• include a supporting plan showing dimension, layout of manholes and position of sewers.  

Please submit this with your application and if it meets our requirements, we’ll refund £200 of your application fee in line with what it would have cost us to undertake the survey ourselves. Also, if a CCTV survey is not required, we will refund you the money.  

No, these types of structures are considered a new development and would require a minimum stand-off of 3 metres from the public sewer. Although commonly called a temporary structure, they often require foundations as well as having utilities facilities such as, electrics, water, gas etc.  

We would consider a temporary structure as something that can be removed instantly to allow us access to the public sewer.  

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. They were officially transferred on 1st October 2011. Lateral drains (which are pipes that only serve one property) continue to be privately owned and maintained up to the property boundary, from which it then becomes a public lateral drain. 

You should presume any sewerage that is located on your land or found during your work is public and owned by us, unless it can be shown to be otherwise. If your property and its sewer was laid after 1st July 2011 it would be assumed private unless formally adopted by us. 

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

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. 

Our maps are indicative and intended for general guidance only. In 2011, a change in legislation required all water companies, including Southern Water, to take responsibility for public shared sewers, many of which were previously privately owned.  

Because these sewers were not originally mapped, their exact locations are often unknown, and some may be situated in less-than-ideal places. We adopted around 19,000 km of these shared sewers, and while we work hard to maintain accurate records, the historical lack of mapping makes it challenging to pinpoint their precise positions. 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.  

Yes, if the sewer is small (pipe less than 225mm wide and less than 3m deep) and the diversion is minor (fewer than three manholes and stays within your property), you can add this to your Build Over Application. 

You can’t do this under a self-declaration because you’re changing the pipe layout. You’ll need to send us a plan showing the new route of the sewer around your extension, following the official design and construction standards. If the diversion crosses into a neighbour’s land, you must get their written permission. 

For bigger sewers (pipes over 225mm or deeper than 3m), you’ll need to apply for a sewer diversion instead. 

Where constructing the new structure within 3 meters 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.