Subsidence, settlement and heave
A stepped crack in the flank wall follows the line where the seller thinks a drain runs. Why is coincidence not a diagnosis?
The stepped crack that follows the line where the seller thinks a drain runs is a coincidence until it is investigated, not a diagnosis. A crack and a supposed drain can share a direction without one causing the other. The survey did not see the buried pipe, and the seller's belief is not a plan. A camera is a further instruction, not part of this visit unless it was agreed. Cause has not been decided.
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?
Stepped cracks are looked at for what they do in the wall: where they start, whether they open at joints, and what the openings and floors nearby are doing. A drain, if it is there, would be judged from a chamber, a trace or a camera, none of which is created by standing back and agreeing the lines look similar. Similarity is not a mechanism.
Keep the crack described as a crack and the drain as an unproved suggestion. Do not dig, and do not tell a lender the drain has undermined the wall. If both need following up, they are two instructions. Roots at a chamber or silt, if seen elsewhere, still do not attach themselves to this crack without a link the visit actually made.
What should you ask your surveyor?
- Did you see a drain on that line, or only hear where the seller thinks it runs?
- Are you leaving the cause of the stepped crack undecided?
- Was any camera or trace included, or is the buried run still unseen?
What are the typical next steps?
- Do not diagnose the stepped crack as drain damage from the matching line alone.
- Record the seller's belief as a belief, not as a located drain.
- If the pipe must be found, agree a trace or a camera as further work.
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
If the crack and the supposed drain line up, is that enough?
No. Lining up is a coincidence until the drain is found and the crack is explained. The survey has not made that link.
Can the seller's memory locate the pipe?
No. Memory is not a survey of the buried run. The pipe stays unlocated on this visit until someone actually traces it on the ground.