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Build Near & Over Agreement For Drainage and Sewers in 2022 - Complete Guide

Building near and over agreements require correct design to satisfy your local water company and council. See our guide for more information.


What are the Rules?

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If any proposed extension or build is within three metres of a public sewer or lateral drain then permission has to be obtained by the water company before any work starts. In order to clarify if your build is close to a sewer or drain you can do the following:  

Your builder will be able to open the inspection chambers once these are found.  

Your can request a sewer map from the water company through their website. 

For more detailed information you can hire a specialist to conduct a CCTV survey which will reveal the condition of the pipes.

The distance is measured from the closest point of the building to the middle of the sewer.



Obtaining Approval

To obtain approval from the water companies, the type of build will be considered.

For single domestic buildings where the pipes measure no more than 150mm you may be able to get a
Self Certificate Declaration if you are confident you meet all the conditions. Otherwise you will have to opt for a Formal Build Over Agreement where more detailed evaluation from the water company will have to be followed.

Details of both these will be in the water companies website It is very important to consider the distance of sewers and drains when planning for a build. Failure to do this could incur problems selling the property and you may be liable for legal action.

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Typical Construction Near a Public Sewer

The typical construction for a building foundation near a public sewer normlly follow the rule of 500mm away from the sewer/manhole or more. If less than 1000mm from the edge of the public sewer, the building foundation should finish at least 150mm below the bottom of the public sewer pipe.

Where the edge of the foundation is further than 1000mm, a 45 degree line can be drawn up to the foundation bottom edge as shown, this can help prevent foundations being deeper than necessarily required. 

It is important to note that each water company may have specific requests regarding the design, when carrying out the build over / build near public sewer application their application officer should contact you or your architect regarding any additional details as needed.

Note that a new building is very difficult to be approved for a build over a public sewer application! Make sure you consider the specifics of your site and seek professional advice from an Architect or Surveyor.

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Typical Construction Over a Public Sewer

In terms of the location of the building foundations relative to the public sewer, the same rules apply on the inside face of the foundation. If less than 1000mm from the edge of the public sewer, the building foundation should finish at least 150mm below the bottom of the public sewer pipe.

Where the edge of the foundation is further than 1000mm, a 45 degree line can be drawn up to the foundation bottom edge as shown, this can help prevent foundations being deeper than necessarily required.

Again, It is important to note that each water company may have specific requests regarding the design, when carrying out the build over / build near public sewer application their application officer should contact you or your architect regarding any additional details as needed.

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What about Where the Building Intersects?

Many common construction details exist for a sewer penetration through the building wall and foundation below ground. 

For a penetration above the foundation within the blockwork , it is common to use a concrete lintel over a square opening for the sewer pipe to pass through (similiar to a structural door opening in a blockwork wall) the square opening is then often filled with uncompacted gravel.

While standard construction detail exist, it is always important that the work be conducted and checked by a professional such as a structural engineer. Every building is different and therefore different problems and challenges need to be overcome by the design.

For more informationon how we can help your project, see below on how to book a free consultation.

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