How to Navigate Build Over Agreements in London

When planning construction or extension works in London, homeowners and developers often encounter an unexpected yet critical requirement: obtaining permission to build over or near public sewers. This process, commonly referred to as a build over agreement, is not simply a formality—it is a statutory safeguard designed to protect essential drainage infrastructure while build over consent assistance in London enables homeowners and developers to understand how these agreements operate, why they are required, and how to manage them efficiently, saving considerable time, cost, and disruption during the project.

This guide provides a comprehensive overview of the build over process in the capital, explaining its legal basis, technical requirements, and the professional support available to help you navigate it successfully.

Understanding Build Over Agreements

A build over agreement is formal approval issued by the local water authority, such as Thames Water, permitting construction work over or close to an existing public sewer or lateral drain. Public sewers are critical assets that must remain accessible for inspection, maintenance, and emergency repairs. Any structure built above them has the potential to restrict access or compromise structural integrity if not carefully designed and detailed.

In London, where high-density development and historic drainage networks are widespread, it is not uncommon for sewers to run beneath private land. Extensions, basement excavations, loft conversions involving structural works, and even modest rear additions can all trigger the requirement for consent if they fall within protected zones around drainage assets.

Why Build Over Consent Is Essential in London

London’s underground infrastructure is complex and, in many areas, dates back over a century. Many property owners are unaware of the presence of shared or public drains beneath their site until planning or building control checks are undertaken. Proceeding without the appropriate approval can result in serious consequences, including:

• Enforcement action by the relevant water authority

• Delays to, or refusal of, building control completion certificates

• Legal and compliance issues when selling or refinancing the property

• Liability for damage to public drainage infrastructure

Types of Projects That Commonly Require Approval

Not all construction projects require a build over agreement; however, many typical developments in London do. These frequently include:

• Rear or side extensions constructed near existing sewer routes

• Basement developments beneath properties with public sewers

• Structural alterations involving new or deeper foundations

• New-build developments on previously undeveloped or brownfield land

Even where construction does not sit directly above a sewer, proximity within a prescribed distance may still necessitate approval. Early investigation through drainage searches and site assessments is therefore essential.

The Importance of Accurate Technical Drawings

One of the most critical elements of a successful application is the submission of clear, accurate, and fully compliant technical drawings. These documents demonstrate to the water authority that the proposed works will not adversely affect the operation, integrity, or accessibility of the sewer.

Professional build over agreement drawings typically include:

• Location plans and block plans clearly identifying the sewer route

• Existing and proposed layouts with precise dimensions

• Foundation designs and construction methodology

• Cross-sections illustrating vertical and horizontal clearance to the sewer

All drawings must comply with the specific technical standards set by the water authority. Incomplete or inaccurate information is a common cause of application delays or refusal.

The Build Over Application Process Explained

Although requirements vary slightly between water companies, the general process in London typically follows a structured approach:

1. Initial Assessment Identification of public sewers through statutory records and CCTV surveys where required
2. Design Coordination Ensuring architectural and structural proposals accommodate sewer constraints
3. Preparation of Technical Documentation Production of compliant drawings and supporting details
4. Submission to the Water Authority Formal application for build over consent
5. Review and Determination Responding to technical queries or conditions prior to approval

Early engagement with experienced professionals can significantly reduce processing times and minimise the risk of revisions.

Common Challenges and How They Can Be Avoided

Applicants often underestimate the level of technical scrutiny involved in build over approvals. Common issues include:

• Incorrect or incomplete sewer location information

• Foundation designs that do not meet authority requirements

• Insufficient provision for future access and maintenance

• Discrepancies between planning drawings and technical submissions

These challenges can usually be avoided through thorough site investigation, coordinated design, and specialist input familiar with London’s drainage authorities.

Professional Support for Build Over Agreements

Given the regulatory and technical complexity, many property owners appoint specialists to manage the process on their behalf. A comprehensive service may include site assessments, liaison with the water authority, preparation of compliant drawings, and full application management from submission through to approval.

For those seeking dependable build over consent assistance in London, professional support can help ensure projects proceed efficiently while meeting all statutory obligations.

Relationship with Planning Permission and Building Control

It is important to note that build over consent is separate from planning permission and building regulations approval. However, the three processes are closely interconnected. Building control bodies will typically require confirmation of water authority consent before issuing final completion certificates where relevant.Co-ordinating these approvals from the outset reduces the risk of costly delays and ensures a clear compliance record for future property transactions.

Long Term Value of Proper Approval

While the process may appear administrative, securing a build over agreement provides long-term benefits, including:

• Full legal compliance and regulatory certainty

• Reduced risk of future disputes or enforcement action

• Increased confidence for purchasers, lenders, and insurers

• Protection of essential public drainage infrastructure

In London’s competitive property market, these assurances can contribute positively to a property’s overall value and marketability.

Final Thought

When appointing a consultant or service provider, it is advisable to choose professionals with demonstrable experience dealing with London-based water authorities, a strong technical background, and a proven record of successful approvals. Transparent communication and a structured approach to applications are also key indicators of a reliable service.

By addressing build over requirements proactively and with the appropriate expertise, the process becomes a manageable component of your development rather than an obstacle.

ParamountBuilt is a home improvement specialist with a passion for helping homeowners unlock the full potential of their spaces.