The short answer

A collapsed drain is a structural failure of the pipe. A plunger or drain rods will not cure it, and treating it as a simple blockage wastes time while the damage grows. The usual signs are a blockage that returns within days, damp or sinking ground above the pipe, and a sewage smell that will not shift. A CCTV drain survey is the reliable way to confirm a collapse and see how bad it is. In many cases the repair needs no digging. We explain what a survey involves before anything is booked, so you can start with the online enquiry form.

Collapsed or blocked: what is the difference?

A blocked drain is a clear pipe with something stuck in it, such as fat, wipes, roots or silt. Once you remove the obstruction, however, water flows normally. A collapsed drain is different. The pipe wall has cracked, crushed or sheared at a joint. It may also have bent out of shape. Even a clear section cannot then carry water properly.

Rodding or jetting a collapsed section can seem to work for a day or two. The crew pushes the obstruction through, but the defect stays. As a result, the same symptoms come straight back. Many households fall into this trap. They pay for repeat clearances on what looks like a stubborn blockage, when the pipe needs a survey and a structural fix. Our guide to a blocked drain pipe, branch or main run helps you judge which problem you have.

The signs that point to a collapse

Several symptoms, especially together, suggest a structural failure, because a blockage rarely causes them all:

Recurring blockages at the same point, which clear and then return within a week or two.
A soft, sunken patch of lawn, path or drive along the likely line of the drain.
Damp patches on inside walls near where a drain runs close to the building.
A persistent sewage smell, indoors or outside, that ventilation does not remove.
More rats or flies near gullies or manhole covers.

No single sign proves a collapse. Subsidence can have other causes, and a smell can come from a dry trap. Even so, since several together justify a proper look underground before more money goes on clearing. Our article on the problems blocked drains cause explains what happens if you leave them.

Why older streets are more exposed

Much of North London’s older housing, for example the terraces in Enfield, Barnet, Wembley and Edgware, has clay drains. Builders often laid clay pipe in short sections with mortar or push-fit joints. Those joints are the weak point. Ground movement, roots and simple age can open them or shear them.

Two factors add to the risk. First, because much of the area sits on London clay, which shrinks and swells with the seasons. That movement stresses rigid buried pipes all the time. Second, many streets share drainage between several homes, so one collapsed section can affect more than one household.

Who repairs it depends on the pipe. Since 1 October 2011, most shared drains and private sewers outside the boundary have belonged to the water company, which is Thames Water across most of North London. A drain that serves only your property, up to your boundary, remains yours. Read who is responsible for blocked drains outside and who is responsible for blocked sewage for the detail. To see why these pipes fail, read why drains block so often in North London. A local example appears in what older clay drains need in Edgware.

No-dig repair or excavation

Many people still assume a collapsed drain means digging up the garden. That is out of date for a lot of cases. The survey result decides the repair:

Localised cracks or displaced joints often need only a patch liner or a full cured-in-place relining run. Either cures a new pipe inside the old one, with no excavation. Our note on why we use drain relining explains the method.
A full collapse means the pipe has lost its shape and material has fallen in. It typically needs digging out to replace the section. The same applies where relining equipment cannot get through.
Access and depth matter as much as the defect. A shallow run under a lawn is a very different job to one under a drive or beside a foundation.

No sensible engineer quotes a repair method before a survey confirms the grade and location of the defect, because a guess can be costly. A fixed answer over the phone, without a look, is only a guess. For more on the camera work itself, see what a CCTV drain survey involves and whether you need a CCTV drain survey.

What it costs to put right

There is no single honest figure for a collapsed drain repair, since the price depends on what the survey finds. It covers how much of the run is affected, whether you need a patch, a liner or excavation, and how deep the pipe lies. It also depends on whether shared sections are involved. Our article on what changes the price of a CCTV drain survey shows how that first step is priced. We agree a fixed price before work starts.

Where we work

Our drain repairs page covers the repair options, while we work across the area, including drain unblocking in Enfield, blocked drains in Barnet and drain repairs in Edgware. Our blocked drains page covers the wider service. For the usual order of methods, read our guide to clearing a blocked drain.

Frequently asked questions

Can a collapsed drain be repaired without digging it up? Often, yes, although it depends on the damage. Localised cracks and displaced joints can frequently take a patch repair or cured-in-place relining through existing access points. A full collapse, or very poor access, may still need excavation. The CCTV survey shows which route applies.

How do I know if my drain has collapsed rather than blocked? Watch for blockages that return within days, a sunken or damp patch along the pipe run, damp walls near a drain line and a persistent smell. However, one sign is not conclusive. Several together are a good reason to book a survey.

Who pays for a collapsed drain outside my house? It depends on which pipe failed, because ownership differs. A drain that serves only your home, up to your boundary, is yours. Most shared drains and sewers outside it belong to the water company. A survey helps show where the fault sits, and your water company can confirm who owns the pipe.