MOVEMENT / READING A CRACK PROPERLY
Most cracks
aren’t subsidence.
A crack is one of the most alarming things a buyer can spot — and one of the most over-diagnosed by anyone who isn’t trained to read it. Here is what actually separates normal movement from something that needs an engineer.
See how findings get rated more generally →THE ANSWER / READ THIS FIRST
The pattern matters more than the crack.
A single hairline crack tells you almost nothing on its own. What a surveyor actually reads is the pattern: where it runs, how it behaves through mortar versus brick, whether it corresponds between inside and outside, and what the building’s age, setting and recent history suggest about the likely cause.
01 / THE USUAL SUSPECTS, IN ORDER OF LIKELIHOOD
What actually causes most cracking.
- 01Thermal movement — materials expanding and contracting with temperature, especially at junctions
- 02Shrinkage — new plaster, render or masonry drying out and settling in its first years
- 03Minor settlement — normal, historic movement that stabilised long ago
- 04Ground-related movement — including subsidence, heave and landslip, genuinely the least common cause
02 / THE FEATURES THAT RAISE A FLAG
Diagonal, stepped,
and growing.
Cracks that step diagonally through mortar joints rather than running straight through brick, that taper (wider at the top), that appear on both sides of a wall in the same place, or that are visibly new and actively widening are the ones that warrant closer attention. Even then, a surveyor is weighing the whole picture — a wall backing onto a mature tree on clay soil reads very differently from the same crack on a modern estate with no vegetation nearby.
03 / WHAT HAPPENS NEXT IF IT'S FLAGGED
Investigation,
not a guess.
If the pattern genuinely warrants it, the report will recommend further investigation rather than offer a definitive verdict a visual, non-invasive inspection can’t responsibly give. That typically means a structural engineer, and sometimes drainage or root investigation to identify a specific cause. It is a slower answer than a same-day verdict, but it is the honest one — subsidence claims that skip this step and go straight to expensive remedial work are a well-documented way to waste money.
04 / WHY THE SURVEY LEVEL MATTERS HERE
A Level 3 goes further into cause than a Level 2 can.
Both levels rate what they see, but the Level 3 Building Survey explains likely cause and how a defect may develop — genuinely useful ground when cracking is present. On period, altered or already-cracked properties, that extra depth is usually worth the difference in fee. Compare Level 2 and Level 3 →
STRAIGHT ANSWERS
Before you ask.
01Does a crack in a wall mean subsidence?+
Usually not. Most cracking is thermal movement, shrinkage in relatively new materials, or minor settlement — normal building behaviour rather than a structural problem. Subsidence is one possible cause among several, and the least common one.
02What does a subsidence crack actually look like?+
Classic indicators include diagonal stepping through mortar joints (rather than straight through brick), cracks that are wider at the top than the bottom, and cracking that corresponds between the inside and outside of the same wall. No single feature is proof on its own — a surveyor reads the whole pattern together with the building's history and setting.
03Will a Level 2 or Level 3 survey diagnose subsidence for certain?+
Neither survey level provides a certain diagnosis on its own — that requires monitoring over months and sometimes boreholes or trial pits. What the survey does is tell you whether the pattern is consistent with subsidence and needs further investigation, or whether it has a more mundane explanation that doesn't.
04What happens if my surveyor flags possible subsidence?+
The report will recommend further investigation rather than proceed on a guess — typically an engineer's assessment, sometimes drainage or root investigation. That recommendation is doing its job properly: subsidence needs a proper diagnosis before anyone spends money fixing it.
05Does possible subsidence mean I should pull out of the purchase?+
Not automatically. Many subsidence histories are manageable once the cause is identified and addressed, and a documented, resolved history is often perfectly mortgageable. What matters is not proceeding on an assumption either way — get the further investigation the survey recommends before deciding.