Why new drainage fails early
Almost all of it comes down to the same thing: the system was never sized for what it ended up carrying. An extension adds bathrooms, a conversion adds kitchens, a garden gets paved and suddenly rainfall has nowhere to go but into a foul run that was designed for one household in 1900.
The second cause is workmanship below ground, where nobody sees it. Falls set by eye instead of with a level, bedding material with stones in it, backfill that was not compacted in layers. Each produces a pipe that settles unevenly, opens at the joints and develops a dip that collects everything passing through.
What we design around
- Where the new run can connect, and whether the existing system has the capacity to take it
- Falls and pipe diameters that will actually carry solids, not just water
- Access points positioned where they will still be reachable in ten years
- Whether surface water can be separated rather than pushed into a foul sewer
- Building over or near a public sewer, which needs agreement with the water company
That last point catches people out regularly. Extensions get held up or refused over a sewer nobody checked for, and the time to find out is while the foundations are still on paper.
How the work runs
- Survey the existing drainage and establish where a new run can connect
- Design the layout with the falls, diameters and access points it needs
- Confirm a fixed price against that design before any work starts
- Excavate, lay and bed the pipework, build the chambers
- Camera the finished run and test it before backfilling and reinstating
Testing before backfill is the step that matters most and the one most often skipped. Any problem found while the trench is still open is a small problem. The same problem found afterwards is an excavation.
Regulations
Below-ground drainage is covered by Part H of the Building Regulations, and installations should follow BS EN 752 outside the building and BS EN 12056 within it. Building over or near a public sewer requires a build-over agreement with the water company.
We tell you what applies to your job before starting, and you get an as-built record showing what was installed and where the access points are. Ask any contractor for that: it saves money on every future job on the property.
What it costs
Installation work typically runs from £600 to £2,500 depending on scope, and the fixed price is confirmed after a site visit. Reinstatement is agreed in advance and included, rather than treated as an extra once the trench is open.
A single new run is often a one or two day job. A full system for an extension or conversion takes longer, and you get the programme with the quote.