Building Over a Shared Sewer?

Building Over a Shared Sewer?

Here is some helpful information if you are considering Building over close to a Public Sewer

Thames Water is responsible for maintaining public sewers, which are sometime located within the boundaries of properties. You must get their agreement to carry out any building work over the top of or within 3 metres of a public sewer to ensure that no damage is caused to it or restrictions made to the way Thames Water use and maintain the sewer.

Here are some answers to questions you may have if you are considering building over a public sewer:

What is a public sewer?

A sewer is a pipe that serves more than one property. All drainage pipes (that connect to Thames Water network) are now public sewers except where only one property is served by the existing pipe, which is known as a drain. A drain is privately owned and maintained to the property boundary by the home owner, once it crosses the property boundary this pipe becomes Thames Water responsibility.

Why do I need to apply?

Public sewers can often fun through private land, under houses and through gardens. Any building works within 3 metres of these sewers needs to be approved by Thames Water to ensure that the sewerage network is not compromised.

Some minor public sewers serving a number of houses, often run along the back of older properties. As these may not show up on the sewer maps it is important Thames Water is contacted at an early stage if it is suspected that a public sewer could be present. This will enable them to discuss and agree any necessary steps required to avoid problems in the future.

Thames Water need to know about any building work near or over a public sewer in order to:

  • Prevent the sewer collapsing. The extra weight of a new building above could cause the sewer to collapse, resulting in structural damage to the new building, interrupted drainage from other properties and wastewater flooding. In these instances the sewer will need to be repaired quickly and this may involved taking down the building.
  • Ensure they have access to carry out maintenance and repairs

 What are my Build Over options?

If you find that your plans could affect a public sewer, you should first consider on of the following options:

  • Avoiding the sewer through modifications to your plans so that the buildings are at least 3 metres away from the sewer. This is often the easiest and cheapest option.
  • Diverting the sewer. If your plans cannot be modified, Thames Water will usually require the sewer to be diverted. In most cases they will have to carry out the work but at your expense.

What happens if building over will not be permitted?

Thames Water will not permit building over on a new detached development – a sewer diversion will be required funded by the developer.

Where feasible, manholes should be removed and piped through.

How does the Build Over Process work?

If having considered the alternatives your only option is to apply to build over a public sewer, a written application form must be made to Thames Water. In some circumstances, they may allow you to build over a sewer subject to the sewer being in satisfactory condition and their written Agreement to do this before you start work.

For all classes, except class 1 domestic, they will need to carry out a Closed Circuit Television (CCTV) survey before you begin work to ascertain whether any repair work is required. Another survey is required when your building is completed to check that the sewer has not been damaged. If you have not obtained their agreement, in certain circumstances, Thames Water have the right to discontinue your works and the buildings erected over the public sewer may need to be taken down. Contacting Thames Water as early as possible in the design process is encouraged to avoid any abortive costs, delays or other problems.

What do Thames Water Charge?

A charge is made for every build over application. The level of charge will depend on the size of the sewer to be surveyed and whether a detailed investigation is necessary. In some cases, where major “strategic” sewers are involved, a formal legal Agreement will be required.

How do I locate a public sewer?

Detailed Planning will liaise with Thames Water in order to locate a public sewer and investigate the site for drainage on site and map both public and private sewers.

What are Thames Water charges?

Here is a list of Thames Water Fees/Charges:

Class 1:   (Domestic)            £343   Class II:           £687

Class 1:   (Commercial)      £687   Class III:         £1,300



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