What Is a Build Over Drain Survey and Why Is It Required?
If you're planning an extension, new build or commercial development near an existing drain or sewer, there's a good chance you'll be told you need a build over drain survey.
At Clearflow Surveys, we regularly carry out build over drainage surveys across Cheshire, Manchester, Staffordshire and the wider North West for homeowners, builders, architects and commercial developers. One of the biggest misconceptions we see is people assuming this is just another “box ticking” exercise for the water authority. In reality, a proper build over survey can identify serious issues before construction starts and prevent costly delays, redesigns or even enforcement action later down the line.
In this guide, we'll explain:
What a build over drain survey is
When it's required
What water authorities like United Utilities are looking for
Common drainage problems we uncover
What happens if you skip the process
Real examples from projects we've worked on across the North West
What Is a Build Over Drain Survey?
A build over drain survey is a specialist CCTV drainage inspection carried out when construction is planned near, over, or adjacent to a public or shared sewer. The purpose of the survey is to:
Assess the condition of the existing drainage network
Identify any defects before construction begins
Provide evidence to the local water authority
Ensure the proposed build won't damage or obstruct the sewer
Confirm the drainage network remains undamaged after construction
Most commonly, these surveys are required for:
Home extensions
Rear extensions
Side returns
New build developments
Commercial construction projects
In many cases, the survey forms part of a build over agreement application with water authorities such as United Utilities.
When Is a Build Over Survey Required?
A build over survey is typically required when:
You're building over a public sewer
You're building close to a shared drain
Your extension affects existing drainage infrastructure
The local water authority requests one as part of a build over agreement
One important point many homeowners and builders don't realise is once a drain crosses a property boundary and serves multiple properties, it usually becomes a shared sewer. We've seen many situations where clients assumed a drain was private, only to later discover it fell under water authority ownership.
That can create major delays if construction has already started.
Why Water Authorities Require Build Over Surveys
Water authorities like United Utilities need to ensure that construction work does not:
Damage public infrastructure
Restrict future maintenance access
Cause collapses or deformation in the sewer network
Increase the risk of blockages or flooding
Create safety risks for nearby properties
A proper survey gives them a record of the drain condition both before and after construction. Without this evidence, you could face:
Delays to approvals
Requests for additional surveys
Expensive remedial works
Enforcement action
In extreme cases, requests to remove or alter completed construction
Water authorities are generally very strict on drainage compliance, particularly where public sewers are involved.
What's the Difference Between a Standard CCTV Survey and a Build Over Survey?
A build over drain survey goes much further than a standard CCTV inspection. While both involve surveying the drainage network internally using cameras, a build over survey typically includes:
Full condition assessment of the pipework, with all defects coded in line with MSCC5 standard
Invert level measurements
Drainage mapping
Identification of shared/public sewers
Coordination with architects and design teams
Recommendations if drainage diversions are required
Pre- and post-construction reporting
What Happens During a Build Over Drain Survey?
Our process usually starts with reviewing any architectural drawings or site plans provided by the homeowner or architect. From there, we:
Carry out a site visit
Locate inspection chambers, manholes and gullies
Access the drainage network using high-definition push rod CCTV equipment
Record footage of the drainage system
Capture invert levels to understand drainage depths
Trace the drainage layout using sonde tracing equipment
Produce a drainage map and condition report
Deliver a full report, typically within 1–2 working days from our site visit
Depending on the project, we can also provide:
GPS mapping
CAD overlays
Dye testing
Drainage design support
This information helps homeowners, architects, and builders understand whether the proposed extension or development is feasible before construction begins.
Common Problems Found During Build Over Surveys
Some of the most common drainage defects we identify include:
Displaced joints
Cracks and fractures
Root ingress
Pipe deformation
Poor previous repairs
Capacity issues
Incorrect drainage falls
Unauthorised connections
Collapsed sections of pipework
In some cases, the condition of the drain means construction simply cannot proceed safely until repairs or diversions are completed.
Real Case Study: Dangerous Gas Line Found Through Public Sewer
One of the most serious issues we uncovered was during a build over drainage survey for a customer requiring approval from United Utilities. During the inspection, we discovered that a public drain had previously been damaged during the installation of a gas line. The gas pipe had effectively been routed through the sewer itself.
This created a major risk:
Wastewater could have entered around the damaged section
The drain structure had been compromised
If the gas line had fractured or leaked, it could potentially have created a serious safety hazard for nearby properties
We immediately worked with the gas authority to have the issue investigated and resolved before construction progressed. Although the project experienced some delay, identifying the issue early prevented a potentially dangerous situation and ensured the development could move forward safely and compliantly.
Real Case Study: Staffordshire Extension Approved Quickly After Proper Surveying
We also worked with a homeowner in Stoke-on-Trent, Staffordshire, who was building an extension over a shared drainage network. We were brought in before construction started to carry out a pre-build drainage survey. During the inspection, we identified several issues within both the shared sewer and parts of the private drainage network.
Working alongside the client and their team, we helped develop a revised drainage plan to connect correctly into the public sewer system. Once the extension slab had been installed, we returned to site to:
Reinspect the new private drainage
Reinspect the shared sewer
Confirm no damage had occurred during construction
The evidence was submitted to United Utilities, and the build over approval process was completed smoothly. Because the surveys had been carried out properly from the start, the customer avoided delays later in the build.
See more on this project here.
The Biggest Mistakes Homeowners and Builders Make
In our experience, the biggest mistake people make is waiting too long to arrange the survey. A build over drainage survey is relatively inexpensive compared to:
Architectural redesign costs
Construction delays
Drainage diversions
Enforcement issues
Excavation and repair work
The earlier the drainage network is understood, the easier it is for architects and builders to design around it properly. Other common mistakes include:
Assuming drains are private
Ignoring invert levels
Building inspection chambers too close to structures
Poor drainage design
Starting work before approval is granted
We've also seen poorly installed drainage systems that later had to be completely replaced due to incorrect pipe angles and bad manhole configurations causing waste retention and recurring blockages.
How Much Does a Build Over Drain Survey Cost?
Most build over drainage surveys start from around £250+VAT, although pricing depends on:
Property size
Extension footprint
Drainage complexity
Number of access points
Length of drainage network being surveyed
Cheaper surveys can often end up costing more in the long run if they don't provide the information required by the water authority. A proper survey completed once, correctly, is almost always the better investment.
What Makes a Good Drainage Survey Company?
A good drainage survey company should do more than simply send a camera down a pipe. They should:
Understand build over requirements
Work alongside architects and builders
Identify whether drains are public, shared, or private
Capture accurate invert levels
Help assess feasibility early
Support drainage redesigns where required
Produce clear, compliant reports quickly
Clearflow Surveys aims to support clients throughout the entire process — from the initial survey through to post-construction sign-off.
Need a Build Over Drain Survey in Cheshire, Manchester or Staffordshire?
If you're planning an extension, new build, or commercial project near a public or shared sewer, it's always better to investigate the drainage early. At Clearflow Surveys, we provide fast-turnaround build over drainage surveys across the North West, including:
Surrounding areas
Our surveys help homeowners, architects and developers move projects forward confidently while meeting local water authority requirements.
Request a Quote
Need a build over drain survey for your project? Contact us today to request a quote or discuss your plans with our team.