How engineers classify cracking in new homes — what's normal shrinkage, and what needs escalating to your developer.
Fine, hairline cracks (under about 1–2mm) at the corners of doors, windows or plasterboard joints in the first year or two are normal drying shrinkage — cosmetic, and easily filled. Cracks wider than 5mm, stepped through brickwork, or paired with a sticking door or sloping floor are worth an engineer's opinion before anyone reaches for the filler.
A brand-new house is still "drying out" for its first year or two: timber loses moisture and shrinks slightly, plaster and screed cure and contract, and the ground under a new foundation settles a small amount as it takes load for the first time. All of this is expected, and building materials are detailed to accommodate it — which is exactly why most new-build cracking is genuinely nothing to worry about. The job is telling that apart from the small number of cases where a crack is telling you something more serious is going on.
Shrinkage cracks are thin and taper off. Movement cracks tend to be wider, step along mortar joints, and often widen at one end.
UK structural engineers commonly grade cracking on a width-based scale, from Category 0 (hairline, under 0.1mm, not usually visible) up through Category 2 (up to about 5mm — cosmetic, easily treated during redecoration) to Category 3 and above (5mm and wider, often needing the crack opened up and properly repaired, sometimes alongside structural monitoring or remedial work). Width isn't the only thing that matters — a thin crack that's actively growing is more significant than a wider one that's been static for years — but it's a useful, consistent starting point for a conversation with an engineer.
| LIKELY JUST SHRINKAGE | GET IT CHECKED |
|---|---|
| Hairline, under ~1–2mm wide | Wider than about 5mm |
| Diagonal, at the corner of a door or window | Stepped through brick or block coursing |
| Along a plasterboard joint or ceiling line | Horizontal, or running through a lintel |
| Appeared once, in the first year or two, and static | Growing over weeks or months |
| No other symptoms nearby | Paired with a sticking door, sloping floor, or brick displacement |
Photograph it against a ruler or coin for scale, note the date, and resist filling or painting over it straight away — that evidence is useful if it needs escalating later. Many cracks move slightly with the seasons, especially on clay soils that shrink and swell with moisture, so a few weeks of simple monitoring often tells you more than a single snapshot. If it's in a new-build and still within your warranty period, log it with the developer in writing regardless — even a cosmetic crack is worth having on record.
No obligation, no jargon — just a clear fixed fee and an honest view of what your project needs.