Chimneys and parapets
What is a corbelled chimney stack, and why do surveyors look at the gable under it?
Corbelling is the way brickwork steps out, course by course, so a stack can sit partly on the wall below. If the courses have dropped or the gable under them is cracked, the support for the stack is part of the question. A straight pot does not answer it.
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?
On terraces and semis the stack often rises off a party or gable wall. The surveyor looks for open joints, a sagging corbel and separation between the stack and the roof slope. They see this from the ground or from a neighbour’s side only if they can go there. They do not load-test the corbel. A comment should say what was visible and whose land they could not enter.
Rebuilding corbelling can mean scaffold and a share of a party stack. The survey does not decide the neighbour’s share. Ask your solicitor about the party wall if work will affect the shared structure, and ask the surveyor whether the gable itself, not only the pots, was the concern. GOV.UK’s party-wall guidance is about that legal process, not about a condition rating.
What should you ask your surveyor?
- Is the concern the corbel, the gable, or only the pots?
- Could you see both sides, or only the street face?
- Would rebuilding affect a shared wall?
What are the typical next steps?
- Do not instruct a bricklayer to cut into a party stack before your solicitor has spoken about the neighbour.
- Photograph the stepping-out courses square on, not from a low angle.
- If access to the other side was refused, record that limit. It is not a pass.
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 corbelling a defect by definition?
No. It is a normal way of building a stack. The defect, if there is one, is movement, open joints or a failed flashing, not the fact that the bricks step out.
Does a crack in the gable mean the stack must come down?
Not on that sentence alone. Ask the surveyor what they think is moving, and what a builder would need to expose.