What are the signs of a collapsed drain?

Repeated blockages in the same place, slow drainage that returns quickly after clearing, a sunken or soft patch of ground over the run, damp or a persistent smell near it, and sometimes rats, which use a broken drain as a route.

Can it be repaired without digging?

Often, yes. Cured-in-place lining repairs cracks, open joints and moderate deformation from inside the pipe. A full collapse where the bore has closed usually needs excavation of that section, but the survey tells you which you have.

What is pitch-fibre and why does it fail?

A tar-impregnated fibre pipe used widely from the 1950s to the 1970s. It deforms under load over decades, going oval and then blistering inwards. Many houses of that era still have it, and it is a common cause of persistent drainage trouble.

Is it my drain or the water company's?

Drains serving only your property and within your boundary are yours. Shared drains and the lateral beyond the boundary largely transferred to the sewerage companies in 2011. A survey that locates the defect settles which side of that line it falls on.

High risk

Updated 30 August 2026

Collapsed Drain

The drain blocks constantly, the ground has sunk above it, and jetting only buys a few weeks.

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What's happening?

A collapsed drain is a section of pipe that has lost its shape — cracked and dropped, joints displaced, or the crown fallen in. Old clay and pitch-fibre drains are the usual victims; pitch-fibre in particular deforms into an oval over decades and eventually blisters inward. Once the bore is deformed, solids no longer clear, so the run blocks repeatedly and no amount of jetting fixes it. The other signature is what happens above ground: soil and bedding wash into the broken pipe and are carried away, leaving a void, and the surface sinks. A patch of lawn, path or driveway that has dropped over a known drain run, combined with repeat blockages, is a collapse until a camera proves otherwise.

What usually causes it?

Age and material failure in Victorian clay or 1960s to 1970s pitch-fibre drainage
Ground movement, subsidence or heave shearing a rigid pipe at a joint
Heavy vehicle loading over a shallow drain with no concrete protection
Root ingress that has widened a crack into a displaced joint over years
Nearby excavation, piling or an extension foundation disturbing the run
Poor original bedding, so the pipe was never properly supported
Repeated aggressive rodding or jetting on a pipe that was already cracked

Is it dangerous?

High, and for a reason people underestimate: the washout. Water escaping from a broken drain carries away the surrounding soil and can undermine paving, drives and, in the worst cases, foundations. It also puts foul water into the ground next to the house. Add the sewage risk from repeated backups and it is not something to manage with an annual jetting visit. Any sudden depression in the ground above a drain should be fenced off, because a void beneath a thin crust can give way.

Can I fix it myself?

Nothing beyond recognising it and protecting the area. Note the pattern: how often it blocks, whether it is always the same stretch, and whether the ground has moved. Look for a sunken patch, a soft spot, or paving that has started to rock. Photograph it. Keep vehicles off any area you suspect, and fence off a visible depression. Chemical treatments and repeat jetting do nothing for a collapse and can make a fragile pipe worse.

When should you call a drainage engineer?

Call a drainage engineer for a CCTV survey as soon as the pattern fits, and treat it as urgent if the ground has visibly sunk or if the collapse is near the house. The survey is the decision point: it grades the defect, measures depth and position, and determines whether the run can be lined or has to be excavated. Where subsidence is involved, your buildings insurer will want that report too, and getting it before any repair matters.

What will the drainage engineer actually do?

Carry out a CCTV survey with a written report, defect grading and a plan of the run
Locate the collapse precisely on the surface with a sonde so any excavation is minimal
Line the run with a cured-in-place liner where the pipe still holds enough shape
Re-round and line a deformed pitch-fibre drain where the material allows it
Excavate and replace the failed section, re-bedding and haunching it correctly
Rebuild or reset the inspection chamber and re-survey to prove the finished run

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Tree Roots In The DrainCaution Outside Drain OverflowingHigh risk Sewage Backing Up Into The Bath Or ShowerEmergency Drains Flooding In Heavy RainHigh risk

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