Drainage and septic tanks
Why does a gulley set against the wall matter more than one in the middle of the patio?
Because a blocked gulley at the wall floods the air brick, the damp-proof course and the footings. One in the patio may flood the patio first. A home survey sees the position and the debris. It does not prove the underground pipe. The repair may be as small as clearing it or as large as re-laying a collapsed outlet. The survey cannot tell those apart.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Downpipes that discharge into a gulley which is higher than the damp-proof course soak the wall by design. That is a building defect you can see. It is not the GOV.UK flood map, which says it does not cover blocked drains. Do not buy flood doors for a gulley that needs lowering.
A drainage firm or a groundworker prices the visible arrangement. There is no national gulley price in the RICS guide. If the rating is 3 because the wall is already damaged, get the quote before legal commitment. A gulley that sits above the damp-proof course is a water path. It is not, by itself, a diagnosis of subsidence.
What should you ask your surveyor?
- Is the gulley above the damp-proof course?
- Is it blocked, or only badly placed?
- Did you rod it? If not, say so.
What are the typical next steps?
- Photograph the gulley and the air brick together.
- Clear debris only if it is safe and the cover lifts. Do not stand in a collapsed chamber.
- Quote the rebuild of the gulley separately from any damp injection. Injection will not lower it.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is a channel drain the same finding?
It is another surface outlet. The survey should say if it falls towards the house. It still is not a camera survey.
Does a new patio “sort” the gulley?
A patio often buries it or raises the ground. Ask the surveyor if that has already happened.