Build-Over Agreements: Paperwork and Records to Keep

When extending a home or adding an outbuilding in England and Wales, groundworks often run close to underground drainage. Since the transfer of private sewers to statutory water authorities in October 2011, many pipes located within private boundaries are legally classified as public sewers or shared lateral drains. If your planned foundations sit over or within three metres of a public sewer, you need formal consent from your regional water authority before work begins.

Why build-over records are critical

Water and sewerage companies have statutory rights of access to maintain and repair their network. If building works damage a public asset or restrict access to it, the undertaker has the legal power to order alterations or, in extreme cases, remove the structure at the owner's expense. Furthermore, Building Regulations sign-off cannot be completed without proof that the sewerage undertaker was properly consulted and agreed to the construction method.

A build-over agreement protects both the network and your home. It ensures foundations bridge the pipe correctly, prevent point loading on fragile clay or plastic drains, and retain sufficient clearance for manholes and inspection chambers. Retaining the complete paper trail ensures you can demonstrate that these conditions were met.

The core documents to keep on file

A complete build-over record is rarely just a single letter. A thorough file will contain technical assessments, formal permissions, and post-work verification:

• Pre-construction CCTV drainage survey: Footage and written report showing the condition, depth, diameter, and exact route of the sewer before work starts.
• Formal application and site layout: The technical drawing submitted to the water company illustrating the proposed foundation design and proximity to the pipe.
• Approved build-over agreement or consent letter: The formal document signed or issued by the statutory water undertaker granting permission to proceed.
• Structural engineering drawings: Detailed designs showing bridge lintels, pile sleeve arrangements, or raft details designed to avoid loading the pipe.
• Post-construction CCTV survey: A follow-up camera inspection confirming the drain was not cracked, displaced, or blocked with concrete during groundworks.
• Final sign-off or closure letter: Written confirmation from the water company acknowledging that post-construction requirements have been satisfied.

Self-certification vs formal legal agreements

The paperwork you receive depends on the pipe size and location. For standard domestic pipes (often 100mm or 150mm diameter) where standard clearance conditions are met, water undertakers often operate an online self-certification or standard consent process. In these cases, you receive a confirmation certificate rather than a complex legal deed.

For larger trunk sewers, deep drains, or situations where an inspection chamber is being relocated or abandoned, water companies require a formal legal agreement. This document may involve site inspections by water board engineers and specific legal covenants. Regardless of whether your approval was a self-certified letter or a multi-page legal deed, the document must be archived securely alongside your local authority Building Control completion paperwork.

Retaining evidence for maintenance and property sales

When selling a property, the buyer's solicitor will review standard enquiries on Form TA6 and commission a CON29DW drainage and water search. If a public sewer is recorded within the boundary and an extension has been built, the buyer's legal team will request proof of the build-over permission. If the original documents are missing, sellers are often forced to commission retrospective CCTV surveys or purchase indemnity insurance policies, which can delay the transaction.

Storing these documents digitally helps keep technical plans, video surveys, and official sign-offs organized in one location. Using an independent platform like Project Passport allows homeowners to maintain an organised digital archive of structural plans and utility approvals alongside their ongoing property records.

Future maintenance also becomes simpler. If blockages occur years later, having the CCTV survey and exact depth measurements to hand saves drain engineers from intrusive digging. Ensuring these records are compiled as soon as works finish protects your investment and ensures future trades know precisely what lies beneath the slab.