Do not use “settlement” for every cause
Drying shrinkage in finishes and settlement of the ground are different processes. NHBC's November 2025 guidance explains that mortar, plaster and concrete can change as they dry, while the building's weight can compress supporting ground. The label should follow an assessment, not replace one. [2]
Ask the builder or inspecting professional what they believe is moving and what evidence supports that explanation. A statement that “all extensions do this” is not a description of the particular crack or an agreed plan for checking it.
Look at the old and new construction together
The structural requirements address how loads reach the ground and how the building accommodates reasonably foreseeable ground movement. [3]
Where cracking appears at the meeting of old and new work, ask the engineer to consider the designed connection and both supporting structures, rather than looking only at the new plaster.
Supply the final structural drawings, any foundation changes made on site and available inspection photographs. Highlight differences between the approved proposal and what was actually built so that the review uses the relevant information.
A practical reporting sequence
- Photograph the location safely, including a wider view and the date.
- Report the symptom to the contractor and the relevant designer, describing any change in doors, windows or floors.
- Ask for a written explanation, a repair or monitoring proposal and a review date.
- Retain the response and report further movement rather than repeatedly covering it over.
This record does not determine fault or prove a defect. Its purpose is to let the people assessing the problem compare observations over time.
When should the concern be escalated?
Cracks that grow, form a stepped or diagonal pattern, or accompany distortion deserve assessment rather than automatic redecorating. NHBC's guidance makes clear that the surrounding symptoms matter, not only the width of the crack. [2]
If there is immediate danger, keep people clear and seek emergency help. Council dangerous-structure guidance distinguishes this from a routine maintenance concern and directs an emergency call where someone is in immediate danger. [4]
Insurance and making good
The Financial Ombudsman Service distinguishes settlement from subsidence and notes that damage can also arise from design, materials, workmanship or lintel failure. The cause and policy wording matter; do not assume that a buildings-insurance subsidence clause covers every extension crack. [5]
Ask who is responsible for the next investigation and how any proposed repair will be documented. Agree making good after the cause has been assessed and any necessary corrective work identified. Keep the final written outcome with the extension's completion records, including any recommendation for continued observation rather than a premature statement that the matter is closed.