Before commissioning a CCTV drain survey for an extension, ask the appointed team which questions it needs to answer. A useful survey brief connects the proposed footprint, the drains being investigated and the design decisions that follow.
Start with the available information and the uncertainty that matters. You may need an existing route identified, an accessible section assessed or information to support a sewer-provider application. Ask the relevant specialist and designer to agree the appropriate investigation and outputs for your project.
Put the extension and drainage information together
Give the appointed team the existing and proposed plans, with a revision and date. Mark any known inspection points, accessible drain routes, previous alterations and available survey references. Identify where the proposed work meets the existing building.
Keep uncertainty visible on the plan. An old drawing, a photograph and an inspection report describe different kinds of information. Record their source and limits so the team can decide what needs confirming before design or pricing proceeds.
Agree the specialist survey brief
Ask what the proposed investigation can establish and what it may leave unresolved. Confirm access arrangements, the areas included and the expected record format. If a part cannot be inspected, ask for that limitation to be identified in the handover information.
Request outputs that the designer can relate to the plans: appropriate location references, report references, relevant footage and a clear account of findings and limitations. The scope and interpretation belong with the appointed competent specialist. Your construction enquiry to us should mention any survey appointment arranged separately.
Check the sewer provider's process
Thames Water's build-over guidance explains that construction over or near its public sewers and lateral drains may require its agreement, and that planning permission does not provide that agreement. Its guidance also warns that design changes may be needed before construction.
First establish which sewer provider applies to the property. Then ask the project team to confirm the relevant process for the actual design. Survey footage can inform that discussion, but it does not provide consent, answer every ownership question or settle the structural design.
Keep a possible build-over arrangement and any diversion proposal clearly identified. Ask the relevant provider and designer which route applies and what information they need. Use their current project requirements when preparing the next submission.
Use a survey-to-design handover register
This original register tracks how information reaches the construction scope. Make one entry for each material question and add an owner, next action and status.
| Record | What to enter |
|---|---|
| Project and plan | Address, proposed footprint, drawing number, revision and date. |
| Survey reference | Specialist, inspection date, report and footage references, investigated scope and limits. |
| Route or condition question | Relevant location, finding or unresolved issue; supporting drawing or report entry. |
| Ownership or provider query | Question referred to the relevant party, correspondence reference and response status. |
| Design response | Appointed designer's required change, additional investigation or confirmed arrangement. |
| Approval record | Applicable provider or other decision, reference, conditions and person checking them. |
| Construction consequence | Work included, outstanding assumption, access requirement and quotation item affected. |
Example: an uncertain route beneath the proposed footprint
Take an owner proposing a rear extension where an existing drainage route is unclear. This is a hypothetical planning example. The survey brief asks the specialist to investigate the agreed accessible scope and explain its limits.
If the report leaves a section unresolved, enter that limitation in the register. The designer can identify the next information needed and consider how it affects the proposal. Send any provider question with the relevant plan and report references, keeping the response linked to that same entry.
Before final construction pricing, update the work schedule from the confirmed design. Show any remaining allowance or exclusion clearly. A quotation based on a fully resolved arrangement should be compared with another quotation using the same information.
Send the handover information with the enquiry
For a house extension construction enquiry, send the postcode, existing and proposed drawings, drainage reports available and the status of designer and provider decisions. Include access and occupancy arrangements. Clearly identify the information still outstanding so the construction package can be discussed on a stated basis.