A collapsed drain can go unnoticed for months. The pipe sits underground, out of sight, quietly failing while the signs build up above the surface.
By the time most people realise what’s happening, the damage has already spread to their garden, their driveway, or the foundations of their building.
The good news is that collapsed drains do give warning signs.
If you know what to look for, you can catch the problem early, get a proper diagnosis with a CCTV drain survey, and fix it before a bad situation becomes an expensive one.
Here are the signs that suggest your drain may have collapsed, what causes it, and what to do about it.
What is a collapsed drain?
A collapsed drain is a section of underground pipe that has caved in, cracked apart, or lost its shape to the point where it can no longer carry waste water properly. The pipe may have folded inward, fractured into pieces, or been crushed by the weight of soil, traffic, or tree roots above it.
Once a pipe collapses, waste water can’t flow through as it should.
It backs up, leaks into the surrounding ground, and creates problems that show up both inside and outside the property.
Some collapses are sudden, caused by a single event like heavy construction nearby. But most happen gradually, with the pipe weakening over years before finally giving way.
Signs of a collapsed drain
No two collapsed drains look exactly the same from the surface, but there are consistent warning signs that drainage engineers see again and again.
If you’re noticing more than one of these at the same time, there’s a reasonable chance the pipe has failed.
Persistent sewage smell
A cracked or collapsed pipe leaks sewage into the surrounding soil.
You’ll notice a foul odour around external drains, manholes, or inspection chambers, and in some cases the smell reaches inside the building through floor drains or ground-floor rooms. The key word is persistent.
Every drain smells occasionally, but a constant sewage smell that doesn’t clear after flushing or cleaning points to something structural.
Recurring blockages
If you keep clearing the same drain and it blocks again within days or weeks, the pipe itself is almost certainly the problem. A collapsed section creates a point where debris catches and accumulates, no matter how many times you clear it with rods or drain jetting.
The blockage is a symptom, not the cause.
Slow drainage across multiple fixtures
One slow sink usually means a local blockage. But when several fixtures in the same area of the building all drain slowly, the problem is downstream in a shared pipe.
A collapsed section restricts flow for everything connected to it, so you’ll notice toilets, sinks, and floor drains all struggling at once.
Gurgling sounds
Water trying to pass through a partially collapsed pipe creates air pockets that produce gurgling and bubbling sounds. You’ll hear these from sinks, baths, or toilets, often when another fixture is draining at the same time.
Gurgling on its own can mean a simple blockage, but combined with other signs on this list it suggests structural damage.
Subsidence or sinkholes
This is one of the most visible signs, and one of the most concerning. When a drain collapses, the surrounding soil washes into the broken pipe, creating voids underground. Over time, the surface above sinks.
You might see dips forming in your garden, driveway, patio, or car park near where the drainage runs. In serious cases, actual sinkholes can open up. If the subsidence is near your building, it can affect the foundations.
Damp patches and mould inside the building
A collapsed pipe running beneath or alongside a building leaks waste water into the ground around the foundations. This moisture migrates through the walls and floor, showing up as unexplained damp patches, rising damp, or mould growth on ground-floor walls and floors.
If the damp appeared recently and doesn’t match any other obvious cause (like a leaking roof or burst pipe), a damaged drain could be the source.
Unusually lush or green patches of grass
Sewage is rich in nutrients. When a collapsed pipe leaks into your garden, the grass directly above the leak grows faster and greener than the surrounding lawn. A strip of noticeably healthier grass running across your garden in a straight line is a classic indicator that the drain beneath it is leaking.
Wet or muddy areas that never dry out
Persistent wet patches, puddles, or waterlogged ground near drainage runs, even during dry weather, suggest water is escaping from a broken pipe below. This is particularly noticeable on paved areas where you can see moisture seeping up through cracks or collecting in low spots that used to drain normally.
Rats, insects, or other pests
A collapsed drain creates openings that allow rats, cockroaches, and flies to access the sewer system and potentially enter your property. Rats in particular are attracted to the standing water and waste inside a broken drain. If you’ve noticed a sudden increase in pest activity, particularly near ground-floor drains or in areas close to external manholes, a collapsed pipe may be providing their entry point.
Cracks in walls or foundations
In the most severe cases, a collapsed drain causes enough ground movement to affect the structure of the building itself. If the pipe failure has caused subsidence beneath the property, you may see cracks appearing in internal or external walls, particularly around ground-floor windows and doors. This level of damage is rare and usually indicates a collapse that has gone undetected for a long time, but it’s the most expensive problem to fix if it’s left any longer.
What causes drains to collapse?
Understanding why drains collapse helps you assess your own risk. Some causes are avoidable, others are a matter of time.
Age and deterioration
Older properties with original clay or concrete drainage pipes are the most vulnerable. Clay pipes were laid in sections with mortar joints, and over decades those joints degrade, the pipe walls thin, and the structural integrity weakens.
A clay pipe that’s been in the ground for 50 to 100 years may look fine from the outside but be one heavy rainfall or one tree root away from failure.
Tree root ingress
Tree roots seek out moisture and grow towards drainage pipes. They enter through cracks and joints, then expand inside the pipe as they grow. The force of root growth can crack the pipe from within, and the root mass fills the bore until the pipe walls give way entirely.
Properties with mature trees near drainage runs are particularly at risk.
Ground movement
Subsidence, soil erosion, and changes in the water table can all shift the ground around drainage pipes. Clay soils are especially prone to this, shrinking in dry weather and expanding when wet. The repeated cycle of movement puts stress on pipe joints and can cause sections to separate or crack.
Heavy loads above the pipe
Drainage pipes are designed to carry a certain load from above.
When driveways are extended, car parks are built, or heavy vehicles regularly cross over drainage runs without adequate protection, the additional weight can crush the pipe. This is common on commercial properties where loading bays or delivery routes have been built over existing drainage.
Poor original installation
Pipes that were poorly bedded, inadequately supported, or laid at incorrect falls are more likely to fail over time. Substandard installation isn’t always obvious until the pipe starts to settle and deform years later.
Severe or repeated blockages
A pipe that’s under constant pressure from blockages is more likely to fail. The hydrostatic pressure from backed-up water stresses the pipe walls and joints, and if the blockage forces water to find alternative paths, it can erode the surrounding soil and undermine the pipe’s support.
What to do if you suspect a collapsed drain
If you’re seeing more than one of the signs listed above, don’t wait for the situation to worsen. Here’s what to do.
Book a CCTV drain survey
A CCTV survey is the only way to confirm whether your drain has collapsed and see exactly what’s happened.
Our engineers insert a camera into the pipe through an access point and record footage of the entire drainage run. The survey shows the location and extent of the damage, whether the pipe has partially or fully collapsed, and whether adjacent sections are at risk of failing too.
You see the footage yourself, so there’s no guesswork about what needs fixing.
Don’t ignore it
Collapsed drains get worse, never better.
The longer a collapse goes unaddressed, the more soil washes into the void, the further the subsidence spreads, and the more likely it is that damage reaches your building or neighbouring properties.
What starts as a manageable repair can escalate into a major excavation project if it’s left for months.
Check your insurance
Many home and commercial property insurance policies cover drain damage, though the specifics vary.
Some cover the repair but not the survey. Some only cover damage caused by a sudden event, not gradual deterioration.
Check your policy before starting work, and make sure you have CCTV footage and a written report to support any claim. Our survey reports are designed to provide the evidence insurers typically require.
Understand who’s responsible
If the collapsed section is within your property boundary, it’s your responsibility to repair. If it’s in the shared sewer beyond your boundary, it falls to the local water company.
A CCTV survey with drain mapping will clarify exactly where the boundary is and where the collapse has occurred.
How collapsed drains are repaired
The repair method depends on the severity of the collapse and the condition of the surrounding pipe.
Pipe relining (no-dig)
For pipes that have cracked, fractured, or partially lost their shape but haven’t fully collapsed, pipe relining is usually the best option. We insert a resin-coated liner into the damaged pipe through an existing manhole, inflate it against the pipe walls, and cure it in place.
The finished liner forms a new pipe inside the old one, sealing all the damage without any excavation. Relining has a design life of 50 years or more, and most jobs are completed in a single day.
Excavation and replacement
If the pipe has fully collapsed and lost its shape entirely, relining isn’t possible because there’s no structure left to support the liner.
In these cases, we excavate down to the damaged section, remove it, and install new pipework before backfilling and reinstating the surface. Excavation is more disruptive and takes longer, but it’s the only option for a total collapse.
Patch repair
For a small, localised area of damage in an otherwise sound pipe, a patch repair can fix the problem without relining the full length.
We position a resin patch over the damaged area and cure it in place, sealing the defect quickly and cost-effectively.
Don’t wait for the sinkhole, contact Clark Drainage today
Most of the collapsed drains we repair could have been caught earlier.
The signs were there for weeks or months before the homeowner or property manager called us. By that point, the subsidence had spread, the damp had taken hold, or the recurring blockages had already caused secondary damage that added to the repair bill.
If anything on this list sounds familiar, call us on 0141 280 3431 to book a CCTV drain survey.
We’ll find out exactly what’s going on underground, show you the footage, and give you a fixed quote for the repair. No guesswork, no obligation, and no nasty surprises.
