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Close Proximity to Assets (Water & Sewers)

Building Over or Near to a Public Sewer

Building Over or Near a Public Sewer

Building Over or Near a Public Sewer Process

The Process
Step 1 -Application & Payments
Please complete the application form and send it to developerservices[AT]niwater[DOT]com with all of the associated documents listed on the application form.
Your application submission will be checked for completeness and you will be issued with details of how to make the payment of the application fee via BACS.
Step 2 - CCTV Survey (for building over and piling works only)
If it is proposed that the affected public sewer is not going to be replaced, we will carry out a CCTV camera survey to check the public sewer’s structural condition. If the affected public sewer is a Clay pipe it must be replaced at the property owner’s expense.
Step 3 - Assessment and Outcome
If your proposal is acceptable we will issue a Build Over / Near a Public Sewer Agreement and approval letter.
If any drainage works are necessary (eg, sewer replacement or manhole relocation), our approval will be conditional, pending completion of these works.
Step 4 - Owner to return signed Build Over / Near a Public Sewer Agreement 
Please return the Agreement with all of the required signatures to developerservices[AT]niwater[DOT]com
NIW will authorise the Agreement and will issue it to the applicant.
Step 5 - Drainage Works (amending NIW infrastructure)
The drainage works should be carried out in accordance with the agreed Method Statement and as detailed in the approved drawings.
Step 6 - Construction
Your works can commence.
When construction has progressed where the pipe protection measures have been installed and remain exposed, please submit an application for an Inspection (SBO-A236-Insp) inclusive of the inspection fee.
NIW will arrange for an Inspection of the work associated with the approved Agreement, inclusive of a CCTV to determine the structural integrity of the affected sewer.
If the work associated with the approved Agreement is deemed satisfactory we will issue a Completion Certificate as confirmation, to keep with your property deeds.

Guidance Notes

It is an offence under Article 236 of the Water and Sewerage Services (Northern Ireland) Order 2006 (as amended Water and Sewerage Services Act (Northern Ireland) 2016), to realign, build over or near watermains, public sewers, pipes and associated works owned and maintained by NI Water unless with the prior consent by NI Water.

If you have located or have reason to believe that a public sewer is within the Protected Strip, which is noted as

  • within 3m or 1.5 times the depth of the proposed structure (whichever is the greater); OR 
  • within 15m if piling is proposed; OR
  • if your proposal involves the reduction or increase of the existing ground level within the Protected Strip, and construction of any building / structure (this includes any non-habitable structures, ie retaining walls) is proposed  within the Protected Strip you MUST consider relocating your building / structure.

You must consider the realignment of the public sewer in the first instance. Please refer to the Realignment of a Public Sewer guidance notes. However, if a realignment is not feasible due to site constraints, please provide evidence of the reasoning behind this decision. This should be included in your application pack when making the application to Build Over / Near the Public Sewer.

If you have considered all the alternatives and the only option appears to be to build over or near the public sewer, please forward your proposals to us for assessment using application form SBO-A236.

Please note that a Building Over / Near a Public Sewer Agreement may not always be permissible.

It should be noted that NI Water will not consider a proposal to build over a public sewer for a new building.

Please determine the exact location of the affected public sewer(s) prior to making a Build Over or Near a Public Sewer application. Failure to do so may result in a delay in the processing of your application.

Where this is not possible NI Water may be willing to determine the location on site. However, this will be at your expense. To avail of this service please email a location plan to waterline[AT]niwater[DOT]com to request the location of the public sewer to be identified on site.

The current fees and charges associated with the Building Over or Near a Public Sewer process, in accordance with the current Scheme of Charges are:

  • Application Fee - this includes appraisal of your proposals (non-returnable);
  • Inspection Fee - payable at the time of submitting the Inspection Application (SBO-A236-Insp) on completion of the work.
  • Request for NI Water to locate the public sewer on site - if applicable.

Please note:

Although we will consider every case sympathetically:

  • it is possible that permission to build over public sewers which are classified as critical public sewers may not be given.
  • it may not be possible to permit a build over / near a public sewer if ground levels are being altered on site.
  • it may not be possible to permit a build over / near a public sewer if future maintenance access to NI Water assets in the locality are diminished.
  • Under no circumstances is construction allowed directly over a pumping main. Restrictions WILL also apply as to how close you can build to such public sewers.
  • Manholes, where possible must be outside the structure. Where this is not possible, they must be sealed at finished floor level and accessible without excavation. Any floor coverings that will need to be removed for access purposes will be replaced at the owner’s expense. 
  • Inspection chambers MUST NOT be constructed on the line of the public sewer.
  • Lateral connections, where possible, should connect to the public sewer outside of the structure.

Permitted Location of Sewers and Lateral Drains in Proximity to Buildings or Structures

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Building Over Non-Critical Public sewers

It may be possible to build over non-critical public sewers, which often run along the back of older properties and are affected by extensions to the rear of the property. In most instances building over/near these public sewers will be permitted, providing that certain structural protective measures are taken. The standard protective measures are as follows:

  • CCTV Survey will be required to determine the existing condition and location of the affected public sewer;
  • Foundations must be taken down to a minimum of 150mm below the public sewer invert level. No structures (footings, walls etc) running parallel, or adjacent to the line of the public sewer will be allowed within 500mm of the public sewer (in plan); and
  • Crossings must be supported using pre-cast (or adequately designed cast in-situ) concrete lintels/beams. (Please refer to the ‘Typical Detail for Building Over a Public sewer’ on page 5)
  • Any clay or damaged public sewer under the proposed building MUST be replaced with a new sewer pipe of an equivalent size (material to be agreed with NIW). A detailed method statement will be required.


Building Close to Critical Public sewers

  • Critical Public sewers are usually defined as large diameter strategic public sewers but may also be classified by material, depth and/or location.
  • Under no circumstances is construction allowed directly over a pumping main. Restrictions WILL also apply as to how close you can build to such public sewers.

Piling Works Near Public sewers (within 15m of a public sewer)

Where piling works are being carried out care must be taken to avoid any damage to the public sewers. The position of the public sewer MUST be established by electronic survey. Should the survey suggest that the public sewer is likely to be within 15 metres of the piling works, trial holes may be required to establish the exact location of the public sewer. Piling systems must be chosen so that resultant vibration is kept to a minimum. A suitable method statement, inclusive of the measures to be taken if the public sewer is damaged, must also accompany the application. 

Applying for a Building Over or Near a Public Sewer Agreement

  • You must submit the application form SBO-A236 via email to developerservices@niwater.com including all of the required information. 
  • Northern Ireland Water Ltd asks for details of:
    • Any mortgage on the property: 
      • in order that we can ensure that the mortgage company joins into any build-over agreement, to avoid a situation where they do not do so and they subsequently repossess the property and sell it  on. If this happened, the mortgage company and the subsequent purchaser could say that:
        • they (in the case of the mortgage company) or the mortgage company from whom they acquired  the property (in the case of a subsequent purchaser) had not signed or been aware of the  buildover agreement.
        • the buildover agreement was not therefore binding on them.
      • The house insurance ( must include buildings cover): 
        • as any home insurance company would want to be informed that the homeowner was entering into  an agreement with NIW to build a structure over or near a public sewer in relation to a property  which was insured with them.
  • Typical requirements for the associated documentation are:
    • The drawings(s) should include: 
      • Site Layout:
        • Be at a scale of 1: 100 or greater.
        • Show the location of existing public sewers and MH’s: 
          • Foul to be shown in red. 
          • Storm to be shown in green. 
          • Combined to be shown in magenta.
        • Show the extent of existing buildings and the proposed new construction (and any other structures that may cause a loading on the public sewer).
        • Indicate changes in Ground Levels.
        • Existing public sewer replacements, to include tie in details to the remaining public sewer.
      • Longitudinal Section:
        • The sections should show:
          • Pipe size. 
          • Gradient. 
          • Material.
          • Manholes.
          • Invert Levels and Cover Levels to Ordnance Datum Belfast. 
        • Existing public sewer replacements, to include tie in details to the remaining public sewer.
      • Protection detail at crossover / potential loading locations:
        • This detail should be site specific, detailing the structural protection to prevent loading on the  public sewer.
      • Please include the floor construction method if the proposal is to build over the public sewer:
        • if it is proposed to have a concrete floor, only suspended concrete floors will be permissible.
    • The drawings should only show details that are relevant to the application, ie: 
      • The location of the proposed Build over/ near in relation to the public sewer. 
      • The proposed protection detail specific to the proposal. 
      • The public sewer with the colour coding as listed above with any private drainage shown in black.
    • If it is proposed to replace the pipe or construct a manhole on the public sewer you must submit a Method  Statement for the work.
    • If you are not proposing to replace the pipe, a Method Statement will be required in case the public sewer is  damaged during the construction process.
  • Your application will be checked during a triage process and if incomplete will not progress until such times as all of the requested information has been received. 
  • Once your application has completed the triage process you will receive a request for payment. 
  • On receipt of payment your application will be assigned to a Wastewater Approvals Technical Adviser

Building Over or Near a Public Sewer Agreement

Once the Wastewater Approvals Technical Adviser has assessed your proposals and agreed the associated detailed design drawings, they will issue a Building Over or Near a Public Sewer Agreement via email.

When you receive the Building Over or Near a Public Sewer Agreement 

  • you will be required to print the agreement and gain all of the necessary signatures prior to scanning and emailing it to developerservices@niwater.com
  • if there is any loan / mortgage on the associated property, the Loan / mortgage provider MUST sign the Building Over or Near a Public Sewer Agreement prior to it being returned to NIW.
  • you must hold and provide current Home Insurance details which must include buildings cover.
  • No work must commence on site until the Assessment and authorisation of the Building Over or Near a Public Sewer Agreement has been completed and the authorised Agreement returned to the applicant.

Completion of the works

  • You MUST submit an SBO-A236-Insp inspection application form to developerservices@niwater.com to request a site inspection, allowing 10 working days’ notice.
  • NIW will triage the inspection application, and if all of the required information has been provided will issue a request for payment of the Inspection Fee. 
  • On receipt of the Inspection Fee your application will be assigned to the Wastewater Approvals Technical Adviser who will be in contact to arrange a mutually suitable date for the inspection.
  • Any excavation and structural protection to the public sewer must not be backfilled or covered until inspected by NI Water. If the excavation has been backfilled, you must excavate the locations of the structural protection prior to the agreed inspection date.
  • If the works are deemed to be satisfactory you will receive a copy of the Final Certificate of Satisfactory Completion of the Building Over / Near a Public Sewer along with a stamped copy of the associated As Constructed drawing.

Please note:

  • NI Water may request a Structural Engineers Report at the developer’s expense.
  • Multi-applications with the same owner / lender for proposed building over proposals that are in the same location and on the same public sewer leg will attract a discount for third and subsequent applications. However, each property will be processed under a separate Building Over or Near a Public Sewer Agreement, with the associated Inspection fee. Further details are available in the current Scheme of Charges and on the application form. 
  • Multiple properties with different owners/lenders must have a separate application.

Further Information

Should you require any further information or assistance please contact Developer Services Servicing Team

Telephone:03457 44 00 88

Email: developerservices[AT]niwater[DOT]com

For more information on how NI Water lawfully processes personal data please view our Privacy Notice at; https://www.niwater.com/privacy/



Typical Detail for Building Over a Public Sewer

  • It should be noted that NI  Water will NOT consider a proposal to build over a public sewer for a New Building.
  • The detail indicated below does not cover all situations which may arise on site and consultation may be necessary with representatives from NI Water prior to submitting their proposals along with the application for consideration.
  • A Building Over or Near a Public Sewer agreement is required if the construction is within the Protected Strip, which is noted as
    • within 3m or 1.5 times the depth of the proposed structure (whichever is the greater); OR
    • within 15m if piling is proposed; OR 
    • if your proposal involves the reduction or increase of the existing ground level within the Protected Strip,

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  • Although we will consider every case sympathetically, it is probable that permission to build over sewers which are classified as critical sewers will not be given. 
  • Further information and application forms are available on www.niwater.com/servicesfordevelopers.asp 
  • This sketch is not to scale.


Build Over Sewer Record Request/ Retrospective Build Over Application

Guidance Notes

  • These notes relate only to sewers and not to water mains.
  • These notes relate only to building work which has already been carried out, and not to building work which is proposed to be carried out.
  • These notes relate to both:

i. Building work which has been carried out over sewers

ii. Building work which has been carried out near sewers.

Unless otherwise indicated, in these notes ‘build over’ includes ‘build near’


Build Over Record Request (Form Reference: BO-RR)

Please note that the applicant is required to submit a Site Location Plan 1:1250 / 1:2500 map (LPSACE map will suffice) with the site boundary clearly indicated in red and relative to an existing feature to allow for the specified area to be easily identified. The area where information is required must be covered in full by the site boundary outlined in red on the site location plan.

There is a cost for this service in accordance with our current Scheme of Charges for a ‘Build Over Record Request’. Our records will be examined to determine if there is any record of a previous build over agreement within the area identified. If there is an existing build over agreement we will issue the applicant a copy of the agreement and no further action will be required. 

However, if no prior build over agreement can be found the next step in the process is completion of the ‘Retrospective Build Over Application Form’ for an extension which has been built over a sewer without prior consent from NI Water.

Retrospective Build Over Application Form (Form Reference: RBO-AP)

a. If it is determined that there is no build over agreement in place, the applicant will need to complete a Retrospective Build Over Application.

b. Date when building work was started:

i. For build overs which have been completed post 2007 a Retrospective Build Over Application must be completed. It is an offence under Article 236 of the Water and Sewerage Services (Northern Ireland) Order 2006 (as amended Water and Sewerage Services Act (Northern Ireland) 2016), to cause any building to be erected over or in the vicinity of a pipe or sustainable drainage system vested in NI Water so as to have an effect on the use or operation of the pipe or system unless with the prior consent of NI Water.

ii. For build overs which have been completed between 1973 and 2007 a Retrospective Build Over Application must be completed. Article 41 of the Water and Sewerage Services (Northern Ireland) Order, 1973 states that any person who wilfully and without the consent of the Ministry (now NI Water), alters or interferes with any works vested in the Ministry for the purposes of this Order shall be guilty of an offence and shall be liable on conviction on indictment to imprisonment for a term not exceeding five years or to a fine or to both.

iii. Build overs completed prior to 1973 will not require retrospective consent.

c. Building Over or Near to Critical Sewers:

i. Critical Sewers are usually defined as large diameter strategic sewers but may also be classified by material, depth and/or location.

ii. Under no circumstances will retrospective consent be given where construction has been carried out directly over a critical sewer, manhole or pumping main. Restrictions WILL also apply as to how close you can build to such sewers.

iii. Please note: Although we will consider every case sympathetically, it is probable that a retrospective build over agreement for sewers which are classified as critical sewers will not be given.

d. Non-Critical Sewers:

In order to adequately assess the application it will be necessary to determine the exact location and condition of the affected sewer. In order to assess the condition of the affected sewer NI Water will complete a site inspection and CCTV survey (including desilt). Applicants will be required to expose pipework in order to determine if a full retrospective build over agreement can be considered. It may be possible to give retrospective consent in respect of structures built over non-critical sewers which often run along the back of older properties and are affected by extensions to the rear of the property. In most instances retrospective consent for building over/near these sewers will be given, provided that certain protective measures are taken. The standard protective measures that should exist are as follows:

i. Building Over (as opposed to Near) Non-Critical Sewers The standard protective measures that should exist are as follows:

  1. CCTV Survey completed by NI Water to determine the condition and actual location of the affected sewer;
  2. Foundations must have been taken down 150 mm below the sewer invert level.
  3. Retrospective consent will not be given if any structures (footings, walls etc.) run parallel to the line of the sewer within 500 mm of the sewer (in plan); and
  4. Crossings must be supported using pre-cast (or adequately designed cast in-situ) concrete lintels/ beams. (Please refer to the ‘Typical Detail for Building Over a Sewer ’on page 3)

ii. Building Near (as opposed to Over) Non-Critical Sewers

  1. CCTV Survey completed by NI Water to determine the condition and actual location of the affected sewer;
  2. Foundations must have been constructed below the sewer invert level.
  3. Retrospective consent will not be given if any structures (footings, walls etc.) run parallel to the line of the sewer within 3.0 metres or 1.5 times the depth of the sewer (whichever is greater), unless by agreement of NI Water.

PERMITTED LOCATION OF SEWERS AND LATERAL DRAINS IN PROXIMITY TO BUILDINGS

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Further Information

Please note:

  • Northern Ireland Water may request a Structural Engineers Report at the developer’s expense.

Documents which should be included within the Retrospective Build Over Application should include:

  • Site Location Plan 1:1250 / 1:2500 map (LPS ACE map will suffice) with the site boundary clearly indicated in red and relative to an existing feature.
  • Site layout plan @ 1:100 or larger, showing location of existing sewer and manholes.
  • Longitudinal Section showing pipe size and material.
  • Foundation details of building (refer to ‘Typical Detail for Building Over Sewer’).
  • Manhole details showing location and depth.
  • Method Statement (including details of calculations and piling system, if applicable).

Enquiries should be addressed to:

Developer Services - Servicing Team

Northern Ireland Water

Ballykeel Office

188 Larne Road

Ballykeel, Ballymena

Co Antrim 

BT42 3HA

Telephone:03457 44 00 88

Email: developerservices[AT]niwater[DOT]com

For more information on how NI Water lawfully processes personal data please view our Privacy Notice at; https://www.niwater.com/privacy/



Typical Detail where consent is sought for an existing structure built over or near a Public Sewer

  • It should be noted that Northern Ireland Water will NOT consider a proposal to build over a public sewer for a New Building
  • The detail indicated below does not cover all situations which may arise on site and consultation may be necessary with representatives from Northern Ireland Water prior to submitting their proposals along with the application for consideration
  • A Building Over or Near a Public Sewer agreement is required if the construction is within 3m (or 1.5 times the depth whichever is greater).
  • Although we will consider every case sympathetically, it is probable that permission to build over sewers which are classified as critical sewers will not be given.
  • Further information and application forms are available on www.niwater.com/servicesfordevelopers.asp
  • This sketch is not to scale.

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