Subsidence, settlement and heave
A glass tell-tale fixed over a crack is itself cracked across. What does that broken tell-tale not measure?
The glass tell-tale that is already cracked across has not measured a rate of movement. It has broken. A broken tell-tale shows that something opened enough to snap the glass, or that the glass failed, but it does not say how fast the crack is moving or when the movement happened. There is no rate in a single broken pane, and the survey should not invent one from the glass.
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?
Tell-tales are useful when they stay in place and are read more than once, with dates. A tell-tale found already cracked has missed that sequence. Nobody can reconstruct the missing readings from the fact of the break. The crack in the wall still needs describing on its own: where it is, and what else around it is open.
Do not quote a speed of movement, and do not say the crack has stopped, because a broken glass cannot show either. If monitoring matters, that means a new tell-tale or another method, read over time, as a further step. The broken one remains evidence that it was fitted and that it did not survive intact, nothing more precise than that.
What should you ask your surveyor?
- Was the tell-tale already cracked when you saw it, with no earlier reading available?
- Can you put any date or rate to the movement from that broken glass?
- How are you describing the wall crack separately from the failed tell-tale?
What are the typical next steps?
- Do not treat the cracked tell-tale as a measurement of how fast the wall is moving.
- Describe the crack in the wall from what you can see now.
- If monitoring is needed, start it properly rather than reading a broken glass.
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 snapped tell-tale prove the crack is still moving?
No. It proves the glass is broken. It does not show whether movement continues, or at what rate, because no sequence of readings exists.
If the glass cracked the day it was fitted, is the wall sound?
Not from that guess. The survey did not see the fitting, and a broken tell-tale still has not measured a rate either way.