Subsidence, settlement and heave
The bay looks to be pulling away at the junction. What should you ask about the gap and the flashing, rather than about a crack pattern?
Ask whether a gap has opened where the bay meets the main wall, and whether the flashing, soakers or mortar at that joint are still closing it. A Victorian bay is a common place for old movement, but the open joint is the defect you can see today. The survey cannot turn that gap into a diagnosis of the ground. It does not test the soil, and one visit does not monitor the bay.
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?
Bays are built against the main wall and often have their own footing, their own lintels and a small roof cut into the wall above. If the bay and the house move differently, the first open line is often the vertical junction, not a diagonal crack across the brick. Water then gets behind a flashing that no longer sits tight. That is a weathering failure you can ask a roofer about, whether or not the ground is still moving. Recording the gap is not the same as proving subsidence, which the Association of British Insurers describes as downward movement of the ground.
The surveyor may only see the junction from the ground or from a bedroom window. They will not usually strip the flashing. Ask them to separate three observations if they can: the width of the gap, the condition of the cover flashing, and any stain inside at the junction. Do not let a contractor’s phrase “the bay has gone” replace those three. If the gap is large enough that the bay roof no longer meets the wall, that is urgent weatherproofing. It is still not a soil test.
What should you ask your surveyor?
- Is the gap at the junction open, or is the flashing still dressed into it?
- Did you see staining inside at that joint, or only the outside line?
- Are you reporting the junction, or saying the ground is moving?
What are the typical next steps?
- Photograph the junction in daylight, including the flashing, before anyone points it up.
- Ask a roofer to look at the weathering separately from any structural opinion.
- Do not tell the seller the bay has subsided because the flashing has parted.
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
Does a sound flashing mean the bay has not moved?
No. A flashing can be re-dressed after movement. It shows the joint was covered, not that the footing is static.
Should you reseal the gap before exchange?
Only if you understand you will hide the evidence. A temporary mastic seal is not a repair of either the flashing or the cause.