Sewer subsided or roots in the sewer? Recognising and tackling it

How does a sewer subside?

A sewer is laid with a uniform gradient towards the street. If part of the pipe subsides, a dip forms where water and waste remain. Possible causes:

• Settlement-prone ground. In large parts of South Holland, the subsoil consists of clay and peat, which compress over the years.
• Difference between house and garden. Many homes are built on piles and hardly settle, while the ground around them does. The pipe can kink or come loose precisely at the transition under the façade.
• Load from above. A driveway used by cars or heavy paving over a pipe not designed for it.
• Excavation work nearby or a pipe that was not properly supported during installation.

How do roots get into the sewer?

Tree roots seek water and nutrients. A sewer pipe is an attractive place for them: it is moist and there is food. Through small openings in joints, connections or cracks, fine rootlets grow inwards. These become thicker and can develop into a dense mat that traps all waste. Older pipes made of stoneware or concrete with many joints, and pipes close to trees or large shrubs, are most susceptible.

Signs of a subsided sewer or root ingrowth

• A blockage that returns within weeks or months after unblocking.
• All drains are running slowly, without any obvious cause inside the house.
• Gurgling drains or a gurgling toilet (see drain or toilet gurgling).
• Sewer smell in the garden, the crawl space or in the house (see sewer smell in the house).
• Subsided tiles, a hollow or a wet patch above the place where the pipe runs.
• Vermin such as rats around the property. A damaged sewer can provide them with a way inside.

Peace of mind with a camera inspection

Whether a sewer has subsided, is broken or is full of roots cannot be seen from the outside. With a camera inspection we look inside the pipe. This is how it works:

1. Cleaning. The pipe is first cleaned, because the camera sees little in a dirty pipe.
2. Inspection. A small waterproof camera goes into the pipe via an access point, manhole or the toilet drain. You can watch on the screen.
3. Assessment. We see whether the pipe is intact, whether it has subsided or shifted and whether roots are growing into it.
4. Localise. We determine how far from the opening the problem is, so that any repair can be targeted rather than having to dig up the entire garden.

And then?

Roots can be mechanically cut out of the pipe. This clears the blockage, but as long as the joint or crack remains open, the roots will grow back. For a permanent solution, the damaged section must be repaired.

Subsidence is usually remedied by excavating the relevant section and re-laying it at the correct gradient or replacing it. How big that job is depends on the location, the depth and what is above it (garden, patio, driveway). After the camera inspection, we discuss what is needed. More about sewer repair.

Is the problem in the part of the sewer under the public road? Then the municipality is usually responsible. Read more about this in blocked sewer: who pays?

Camera inspection in your area: The Hague centre or Delft.