A CCTV drain survey in Farnborough: what we found

This case study is based on an approved, redacted survey summary. Identifying property, client and drainage-reference details have been removed. The findings apply to this surveyed property and should not be assumed to apply to another home.

A CCTV drain survey at a home in Farnborough gave a mixed but useful picture: the foul drains within the property were generally in good structural condition and flowing satisfactorily, while issues were found in a shared route towards the public sewer and at the ends of surface-water pipes leading towards presumed soakaways.

No blockage or surcharge was seen during the inspection. However, the survey identified matters that should be addressed or checked before planned extension works.

What the camera found inside the private foul drains

The private foul drainage serving the house was made up of plastic pipework and inspection chambers. The camera recorded these private pipes as hydraulically serviceable, with no recorded cracks, deformation, significant joint movement or deposits.

The inspection chambers also appeared sound. Their benching (the sloping surfaces that direct flow into the channel at the base of a chamber) was intact, with only minimal silt recorded.

For the homeowner, this was reassuring evidence that the foul drains within the boundary did not show a present need for repair or replacement. As with any buried pipework, that is not a guarantee against future damage from movement, loading or building works. The key point was that there was no current indication that this private section needed work before an extension, provided it is protected during construction.

The more important issue: the route towards the public sewer

The surveyed drainage included both plastic and clay pipework. The camera recorded misaligned joints, root ingress, a crack and a broken section of clay pipe close to a public manhole.

A displaced joint is a joint where adjacent pipe sections are no longer properly aligned. Even a relatively small lip can catch debris. Roots can enter through gaps at joints or defects, and may contribute to future restrictions or leakage.

Although the pipe was still flowing on the survey day, the broken section and roots make it more vulnerable to blockage and possible escape of foul water into the surrounding ground over time.

The surveyor’s notes indicated that only an initial part of this run was private, with most of the defective clay section treated as a public lateral drain. A lateral drain is the pipe that carries wastewater from a property towards the public sewer; responsibility can change along its length.

The exact adoption point was not visible in the survey, so the report recommended confirming responsibility with the local water authority using drainage-search information and the CCTV evidence. On the information available, the authority should be asked to review the defects in the public portion for repair.

A public sewer close to proposed building work

The survey also recorded a public clay foul sewer and public manhole near the proposed building works.

Roots were visible at several joints in this public sewer, and a fracture with associated roots was recorded. These defects did not appear to obstruct flow at the time of the inspection, but the report recommended that the local water authority review them for programmed repair.

This part of the survey matters particularly where an extension is planned. The survey identified potential conflicts between the public drainage and the proposed works. The drawing was not to scale, so the separation between new foundations and the sewer must be measured on site and checked against the final design.

The homeowner’s designer and conveyancer should check the authority’s build-over or build-near requirements before foundations are designed or built. A build-over agreement is likely to be needed if the proposed works fall within the authority’s relevant distance from the public sewer or manhole. The final requirement must be confirmed with the local water authority.

What the survey could not confirm about the soakaways

The surface-water pipework was thought to discharge to soakaways. A soakaway is an underground structure that allows rainwater to disperse gradually into surrounding ground.

The surface-water pipes were flowing freely when inspected. But the camera could not see into the presumed soakaway ends because the image became obscured by roots. This left three important unknowns:

• the exact locations of the soakaways were inferred rather than physically confirmed;
• their internal condition and capacity could not be assessed; and
• roots were already visible near the ends of some of the pipe runs.

There was no recorded loss of performance on the day. Nevertheless, root growth and unconfirmed soakaway condition create a medium-term risk of reduced infiltration, slower drainage and occasional ponding in heavy rain.

The recommended next step was to mechanically cut roots at the affected private surface-water pipe and install a suitable barrier at the entry point. Before new works proceed, the soakaways should be exposed and accurately located. If a soakaway is found close to proposed foundations, it may need to be relocated or reconstructed to suit the final layout, supported by appropriate infiltration testing.

For homeowners considering new drainage or soakaway design, our guide to BRE 365 percolation testing explains how ground infiltration is assessed.

What this means for homeowners nearby

This survey does not show that neighbouring homes have the same drainage layout or defects. It does, however, illustrate several checks that can be valuable for older and newer properties alike:

• private pipes can be in good condition even where a shared or public section has defects;
• responsibility may change part-way along a pipe, so it is important not to assume ownership from a plan alone;
• a drain that is flowing today can still contain roots, displaced joints or fractures worth monitoring or reporting;
• soakaway positions should be confirmed before extensions are designed; and
• a public sewer close to an extension footprint can affect foundation design and approvals.

A CCTV drainage survey provides a record of accessible pipework and can help separate confirmed findings from assumptions that need further investigation. Where a repair is needed on private pipework, the appropriate option may range from local repair to drain relining, depending on the confirmed defect, pipe condition and access. A survey finding alone should not be treated as an automatic instruction to repair.

Recommended actions from this survey

For this property, the practical priorities were to:

1. provide the CCTV evidence to the local water authority and ask it to confirm the public/private responsibility split and review the recorded public-asset defects;
2. check the proposed extension design against the confirmed position of the public sewer, public manhole and soakaways;
3. consult the local water authority’s build-over or build-near process before the affected building works proceed;
4. cut roots and install a suitable barrier at the affected private surface-water connection;
5. expose and accurately locate the soakaways during the design or groundworks stage, with infiltration testing if new or altered soakaway provision is needed; and
6. keep inspection chamber covers accessible after any building work so future cleaning and inspection remain possible.

If you are planning an extension or investigating drainage concerns in Farnborough, request a quotation for a CCTV drainage survey or appropriate follow-up investigation.