Buying a house in London: is a drain survey worth it?

What your surveyor does not do

A standard homebuyer report or building survey may lift an accessible cover and note what is visible. It does not put a camera down the run, and it will usually say so in the limitations.

That means the condition of the below-ground drainage, which is one of the most expensive things on a property to put right, is the part nobody has looked at.

Which properties most need it

• Anything built before about 1940, so vitrified clay with jointed lengths
• Mature trees anywhere near the run, front or back
• Clay subsoil, which covers much of south and west London
• Any history of drainage problems mentioned by the seller
• Extensions, which frequently sit over the original run
• Basement conversions, where pumped drainage adds mechanical failure modes

In practice that is most of the housing stock in Dulwich, Wandsworth, Richmond and similar areas.

What a finding is worth in negotiation

A survey does one of two things. Either it comes back sound, and you have bought certainty for £300 plus VAT. Or it finds a defect with a position, a depth and a severity, which is a documented cost you can put in front of the seller before exchange.

Sellers can dispute an opinion. They struggle to dispute footage with a locator reading. Either outcome is worth the fee.

Timing

Before exchange, and ideally alongside the building survey so both reports arrive together. Afterwards it is still useful for planning work, but you have lost the negotiating position, and a collapsed drain discovered after completion is entirely your problem.

What to ask for

Footage of the whole run rather than the first few metres, positions and depths recorded with a locator, and a written summary written so a surveyor or solicitor can use it. Footage with no interpretation is hard to act on.

See what our surveys include or what the camera actually finds.

New builds and recent conversions are not exempt

The assumption that a recent build has sound drainage does not survive contact with the evidence. New connections into old public sewers, poorly bedded pipework backfilled by a groundworks crew in a hurry, and a run laid with almost no fall are all things we find on properties less than ten years old.

Conversions are worse again: a bathroom added in a former bedroom needs a waste run to somewhere, and where the shortest route was the only route, the fall suffers. That is the defect behind a great many shared stack complaints in the years after a conversion sells.

If the property still carries a warranty, a survey is what turns a suspicion into a claim while the cover is live.