Subsidence, settlement and heave
What should you ask about a diagonal crack that starts at the corner of a window?
Ask what else is happening at that opening: a dropped lintel, a local settlement, or a crack that continues past the window into the wall. A diagonal crack from a corner is a common place for stress. It is not, on its own, subsidence. The Association of British Insurers describes subsidence as the ground moving down under the building. One crack at a window does not prove that.
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?
Openings concentrate stress. A lintel that has slipped, a timber lintel that has rotted, or a frame that has been replaced can crack the corner without the foundations moving. A crack that is wider at the top, stepped through several courses, and repeated on the same side of the house is a different pattern. The survey should say which pattern it saw. It cannot date it on one visit.
Do not write “subsidence” to the seller if the survey said “crack at window, cause not established”. Ask whether a lintel or a drain is the nearer question. There is no RICS price for a new lintel or for underpinning. Quote only after someone competent has said which it is.
What should you ask your surveyor?
- Does the crack stop at the opening, or continue through the wall?
- What did you see of the lintel?
- Are you using the word subsidence, or describing a crack?
What are the typical next steps?
- Keep the lintel, the drain and the ground as separate questions until one of them is evidenced.
- Do not underpin a house because a window corner is cracked.
- Photograph the whole crack, not only the corner.
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 hairline crack in plaster at a window the same thing?
Often it is shrinkage or a joint in the board. The survey should say if it is only in the plaster.
Does a new window cause this crack?
A replacement window can disturb the opening. The papers do not prove the crack, and the crack does not prove the papers are missing.