10 Warning Signs Your Building Needs Structural Repair

Buildings tell you when something is wrong. Most owners only notice the obvious — a long diagonal crack, a door that won't close, a damp patch that keeps coming back. By the time those signs are unmistakable, the underlying problem has often been developing for years.

This is a field guide to the structural warning signs that warrant a call to a chartered engineer, and the symptoms that are merely cosmetic. Use it as a first-pass diagnostic — but for anything in the red zone, get a professional inspection.

The 10 warning signs that matter

1. Diagonal cracks wider than 5 mm

Cracks that run diagonally across walls — especially around door and window openings — usually indicate differential movement in the foundations. A hairline crack is rarely an emergency. A crack you can fit a R20 coin into is.

2. Cracks that pass through the brickwork itself, not just the mortar

Stepped cracks following the mortar joints are common and often cosmetic. Cracks that split bricks vertically are a sign of significant structural force.

3. Doors and windows that suddenly stick

If a door has worked perfectly for ten years and now drags on the frame, the frame is no longer square. That means the wall around it has moved.

4. Sloping or springy floors

Place a marble on the floor. If it rolls consistently in one direction, the joists or supporting beams beneath have deflected. Springiness when you walk indicates the joists are undersized, over-spanned, or rotting.

5. Sagging or bowed roof lines

Look at the ridge of your roof from across the street. A dip or curve suggests rafter failure, purlin sag, or a wall plate moving outward. Roofs do not recover on their own.

6. Gaps opening at wall-to-floor or wall-to-ceiling junctions

A visible gap between skirting and floorboards, or coving and ceiling, that wasn't there a year ago is movement — not shrinkage.

7. Bulging or leaning walls

Hold a spirit level against the wall vertically. If the bubble runs significantly off-centre, the wall is out of plumb. Bay window walls are particularly prone to this.

8. Recurring damp in the same spot

Damp that comes back after every repair often indicates a structural defect — a failed lintel, a cracked external skin allowing water ingress, or settlement opening up a wall cavity.

9. Visible separation between extension and original house

Extensions sometimes settle at a different rate to the main house. A small expansion gap is normal; a visible crack running floor-to-eaves is not.

10. Internal cracks that reopen after redecorating

If you have re-plastered the same crack twice in three years, the wall is still moving. Cosmetic repair will not fix a structural problem.

What is probably not structural

• Hairline cracks in fresh plaster (drying shrinkage)
• Cracks along the joints between plasterboard sheets
• Small cracks at the corners of windows and doors that don't grow
• Surface cracks in render that don't penetrate the masonry behind

If in doubt, photograph the crack, place a small piece of tape across it dated with today's date, and check it in 6 weeks. If the tape has split, the crack is live.

What to do next

1. Document the symptoms with photos and dates.
2. Note any recent triggers — nearby excavation, a leak, a heatwave, tree removal.
3. Commission a structural inspection report from a chartered engineer.

An inspection typically costs R8,000 – R18,000 and is far cheaper than the consequences of ignoring early warning signs. For severe symptoms — a wall visibly leaning, a floor that has dropped, a ceiling sagging — evacuate the affected area and call an engineer the same day.

Insurance and subsidence claims

If movement is recent and significant, contact your household insurer before commissioning private investigations. Most policies cover subsidence assessment and remediation, but require their nominated assessor to attend first. An independent engineer can still be valuable as a second opinion later in the process.

Frequently Asked Questions