Structural Cracks: Quick Guide for UK Homeowners
Notice a line in your wall or floor and wonder if it’s just cosmetic? Not all cracks are harmless – some point to real structural problems. In this guide we’ll show you how to tell the difference, measure the crack, and decide whether a structural engineer is needed.
How to Measure a Crack Correctly
First step: grab a ruler or a simple crack‑width gauge. Measure the widest point of the crack, not the narrowest. Write down the width in millimetres – a 0.5 mm line is usually just drying shrinkage, while anything over 2 mm could mean movement in the building’s frame.
Do the measurement at three spots: the top, middle and bottom of the crack. If the numbers jump around, the crack is expanding unevenly, which is a red flag. Take a photo with a ruler next to the crack; this helps a professional see the scale without visiting first.
Track the size over time. Check once a week for a month. If the crack grows more than 1 mm, note the change. Consistent growth means the building is still moving and may need repair.
When a Crack Means You Need a Structural Engineer
Not every line needs a full‑blown investigation, but look out for these signs:
- Width over 3 mm on an interior wall or floor.
- Cracks that zig‑zag (often called stair‑step cracks) in brickwork.
- Horizontal cracks in foundations or basement walls.
- Doors or windows that stick after the crack appears.
- Water seepage near the crack, which can worsen structural damage.
If any of these show up, call a qualified structural engineer. They’ll assess load‑bearing walls, foundation depth, and soil movement. In many UK cases, subsidence or poor ground conditions are the culprits, and early professional input can save thousands.
While waiting for the engineer, try to keep the area dry and avoid heavy loads near the crack. Don't attempt DIY fixes like plastering over the line – you’ll just hide the problem, not solve it.
Other common causes of structural cracks include:
- Rapid temperature changes causing concrete to expand and contract.
- Incorrectly mixed cement or low‑quality bricks.
- Ground movement after nearby construction work.
Regular maintenance helps. Check your garden drainage, keep trees trimmed away from foundations, and ensure your home’s roof is in good shape – water leakage can add unwanted weight and trigger movement.
Bottom line: a crack is a warning sign, not a design feature. Measure, record, and if the crack fits any of the red‑flag criteria, get a structural engineer on board fast. Early action stops a small problem from turning into a costly repair.
