Drainage in Victorian terraces: what London’s housing stock does to pipes

One design, repeated a million times

The terraced housing built across London between roughly 1850 and 1910 drains through vitrified clay, laid in short lengths with jointed connections, usually running under the front garden to a lateral or along the rear of the plot. It was a good system and much of it is still working.

What it was not designed for is a century and a half of ground movement, mature trees, four flats where there was one household, and a side-return extension built over the run.

Fault one: open joints

Clay is rigid. The ground it sits in is not. Seasonal movement, particularly on the clay subsoil across south and west London, gradually works joints apart. An open joint does two things: it lets groundwater and soil in, and it gives roots a way through.

This is why root ingress is the single most common finding on camera in period housing, and why the repair that actually ends it is lining rather than annual cutting.

Fault two: the shared lateral

Terraces frequently share a drain run before it reaches the sewer. That has two consequences worth knowing.

First, a blockage in one house can be caused by something three doors along. Second, since 2011 most shared drains and laterals in England belong to the water company rather than the owner, so a fault there is often not your bill at all. We set that out in who is responsible.

Establishing which side of the boundary a fault sits on is therefore part of the diagnosis, not an extra.

Fault three: the extension over the drain

Side-return and rear extensions are near-universal in these streets and very often go over the original run. It works fine until the day it blocks, at which point the access that used to be in the garden is under a kitchen floor.

If you are extending, this is the moment to reroute or to add an access point that will still be reachable. If you have already extended, a camera survey tells you where the run goes before anyone lifts anything. We see the consequences constantly in Fulham, Wandsworth and Balham.

Fault four: conversion without upgrade

A house divided into flats still drains through the pipework built for one family. Four kitchens and four bathrooms now use a run sized for one of each, and the kitchen or bathroom that got moved during the conversion usually ended up with a long shallow waste run that collects residue.

The pattern is heaviest in Islington, Hackney and Lambeth, where conversion density is high.

What to actually do about it

If your drain has never given trouble, nothing. If it has blocked twice, survey it rather than clear it a third time. If you are buying, survey before exchange, because a collapsed drain found afterwards is a great deal more expensive than one found before.

See what a survey involves or coverage by area.

We work these streets regularly. More detail on CCTV drain surveys in Islington, CCTV drain surveys in Lambeth and blocked toilets in Lambeth.