Crack guidance
Is my crack subsidence, or something else?
Find out what the crack in your wall actually means. Learn to tell thermal movement, plaster shrinkage and failed lintels apart from ground movement so you know whether to worry.
When a crack is just a crack
Most cracks in Hampshire homes have nothing to do with the ground moving. Brickwork expands when it warms and shrinks when it cools. A thermal movement crack or subsidence are two very different things, but they can look similar if you do not know where to look. Thermal cracks tend to be thin, follow mortar lines, and open slightly in summer before closing again in winter.
Plaster behaves differently from masonry. Plaster shrinkage cracks new build homeowners notice are usually hairline and map across the surface in random directions as the material dries out. They sit on top of the wall rather than running through it. A fingernail will catch in them, but they rarely indicate anything structural. Older homes in Winchester or Romsey with lime plaster may show these patterns after a room has been redecorated or heated quickly after a cold spell.
The first step is simply noticing where the crack sits, how wide it is, and whether it changes with the seasons. That information matters far more than the panic that often arrives first.
Lintels, arches and wall ties
Steel supports above windows rust over time. When they expand, they push the brickwork outward and upward. Lintel failure cracks above window openings typically run horizontally along the top of the frame or step diagonally from the corners. The bricks might look like they are bowing forward. This happens frequently in older terraces around Southampton and Portsmouth where original steel was used without modern protection.
Wall ties hold the inner and outer layers of a cavity wall together. When those ties corrode, the outer skin can bulge. A wall tie failure crack pattern usually shows as horizontal cracking along bed joints, sometimes with a slight outward lean visible against a straight edge. It looks alarming, but it is a repair a specialist mason handles routinely. It does not mean the foundations have shifted.
Dropped arches over doorways or windows can happen because of simple age, vibration from heavy traffic, or poor original construction. An arch that has flattened slightly does not automatically point to subsidence. The shape of the distortion tells a specialist far more than the mere presence of a crack.
What points toward ground movement
Subsidence cracks behave differently. They tend to be wider at one end than the other, often tapering from several millimetres down to nothing. They frequently run diagonally through both bricks and mortar rather than following the neat lines of the wall. You might see them radiating from the corners of doors and windows, where the wall is weakest.
In Hampshire, the geology varies sharply. Homes built on clay in Fleet or Chandlers Ford move as the soil dries in summer and swells in winter. Properties near the coast in Gosport or Hythe might sit on filled ground that compresses unevenly over decades. A crack that grows steadily wider, causes doors to stick in their frames, or appears suddenly after a long dry spell carries more weight than one that has sat unchanged for years.
A structural engineer performing a crack diagnosis in Hampshire will measure these widths, check levels across the floor, and look at the soil type before drawing any conclusions. Guessing from a photograph is never enough.
Who should look at your home
A general builder can repair plaster, repoint mortar, and replace a rusted lintel. But diagnosing why a wall cracked requires someone who understands foundations, soil mechanics, and load paths. If you suspect ground movement, a structural surveyor or a specialist subsidence engineer is the right person to ask.
An independent opinion costs money, but it prevents expensive mistakes. A builder might underpin a wall that only needed a new lintel. Alternatively, someone might fill and paint over a crack that signals a failing foundation. In towns like Basingstoke, where chalk and clay meet, or Fareham, where old brickfields left variable ground, local knowledge matters. A specialist familiar with Hampshire soils will know what to expect before they even dig a trial hole.
You do not need to commit to repairs by asking for an assessment. The survey produces a report explaining what is happening and what options exist. From there, you decide how to proceed, whether that involves resin injection, screw piling, traditional underpinning, or simply monitoring the crack over a few months.
What to look for around your home
Cracks appear for many reasons. Some reflect normal wear, while others hint at shifting foundations. These are the physical signs you can check yourself before calling anyone.
- 1
Diagonal cracks at corners
A crack wider at the top than the bottom, stepping through bricks near a window or door corner, can suggest differential movement below.
- 2
Sticking doors and windows
Frames that jam suddenly, especially after dry weather, may mean the surrounding wall has shifted slightly out of square.
- 3
Horizontal cracks above windows
A line running along the top of a window opening often points to a rusting steel lintel expanding rather than ground movement.
- 4
Hairline plaster crazing
Fine, shallow cracks scattered across a newly plastered ceiling or wall usually result from the material drying too fast.
- 5
Gaps at skirting boards
A space opening between the floor and the skirting board can indicate the floor dropping or the wall lifting away from it.
Questions about cracks in your home
Could my crack just be thermal movement rather than subsidence?
Yes. Brickwork expands and contracts with temperature changes. Thermal cracks are usually thin, follow mortar joints, and change slightly with the seasons. Subsidence cracks tend to be tapered, diagonal, and grow progressively wider over time.
How do I tell lintel failure or wall tie rust from ground movement?
Lintel failure produces horizontal cracking directly above the window or door. Wall tie corrosion causes horizontal cracks along bed joints and a visible bulge in the outer wall. Ground movement usually creates diagonal cracks that cut through both bricks and mortar.
Is a hairline crack in new plaster anything to worry about?
Rarely. New plaster shrinks as it dries, leaving fine surface cracks that do not penetrate the wall behind them. If the crack is wider than a millimetre or runs deep into the masonry beneath, it warrants a closer look from a specialist.
What patterns would make a specialist suspect subsidence instead?
Tapered diagonal cracks radiating from window or door corners, cracks that pass through bricks rather than just mortar, and signs that align with seasonal drying all raise suspicion. Sticking doors and sloping floors add further weight to the concern.
Do I need an engineer or can a builder tell me what it is?
A builder can fix superficial damage, but identifying the cause of structural cracking requires an engineer or specialist surveyor. They understand soil behaviour and load paths, which prevents unnecessary repairs or missed problems.
If it turns out not to be subsidence, what should I do about the crack?
The repair depends on the cause. A failed lintel needs replacing. Corroded wall ties require new stainless steel ones. Thermal cracks might only need flexible filler and redecoration. A specialist report will specify exactly what is required.
Does reporting a crack to my insurer commit me to a claim?
Notifying your insurer records the issue but does not force you to claim. However, once notified, the information stays on your record. Many homeowners prefer paying for an independent survey first to understand the problem before involving insurance.
How much does an independent opinion on a crack cost in Hampshire?
Fees vary by property size and location. A basic visual inspection might start around a few hundred pounds, while a full structural survey with level monitoring costs more. Contacting a local engineer directly gives you an exact figure for your home.
Get a clear answer about your crack
Send details of what you have noticed at home. A specialist firm will review the information and advise whether a site visit is necessary. There is no obligation to proceed with any work.
- No obligation to proceed
- Specialist firms handle the work
- Local Hampshire knowledge