Signs that deserve prompt attention
NHBC's November 2025 guidance highlights cracks that are stepped or diagonal, extend through both sides of a wall, increase over time or accompany distorted openings. These are reasons to seek assessment, not a diagnosis of subsidence by themselves. [1]
RICS also identifies newly sticking doors or windows and changing floor levels as possible movement signs. Where there is no clear explanation, it recommends specialist help. Do not dismiss a new symptom merely because a different crack elsewhere was previously described as cosmetic. [2]
Avoid a single safe-width rule
A width guide can help describe damage, but it cannot replace consideration of the building and whether movement is active. Record what is happening and ask the inspecting professional to explain the significance of the complete pattern. Do not turn a general online illustration into permission to ignore a rapidly changing defect.
For an enquiry, take photographs from a safe position showing both the wider location and a close view. Add the date first noticed, whether it has changed, recent building work and any known leak or nearby excavation. These are briefing suggestions, not a method for self-certifying the building.
Inspection and monitoring
A structural survey may begin visually and identify a need for opening-up or further investigation. Confirm whether the commissioned service is an initial inspection, diagnosis, monitoring or repair design. A first visit may not answer every question about concealed construction. [3]
In suspected ground-movement cases, the Financial Ombudsman Service describes investigations such as foundation exposure, ground testing, drain inspection and crack monitoring. Seasonal monitoring can be relevant, but it is not a blanket instruction to leave an apparently unsafe situation unattended. [4]
When it is urgent
If part of the building appears unstable, keep people away and seek urgent assistance rather than approaching to measure the crack. Council dangerous-structure services deal with structural danger; Hillingdon's guidance directs people to call 999 where someone is in immediate danger. [5]
For movement appearing during building work, tell the person controlling the site and the structural engineer immediately. Ask them to assess whether the affected operation must stop and what protection is needed before it continues.
Repair after understanding the cause
Ask the professional to distinguish cosmetic making good from work needed to restore support or address an underlying cause. Request a written conclusion, any further investigation and a clear review point.
Keep the report, photographs and subsequent observations together. Where monitoring is advised, ask who will review the results and what changes should trigger contact. Simply filling a crack and losing the record is not a useful way to establish whether the building has stabilised.