Weald and Gault clay Dene holes Brickearth and sand Old pits and fill Marsh and alluvium Ragstone and tile hung Cliffs and landslip Orchards and hop land Railway ground Oasts and barns Crack widths Urgent or not Newer houses Common questions Advice and guides
Movement survey Crack monitoring Drainage CCTV Underpinning Resin injection Screw piling Concrete cracking Wall tie replacement Buyer's report
Maidstone Gillingham Chatham Rochester Ashford Gravesend Dartford Tunbridge Wells Tonbridge Sevenoaks Canterbury Herne Bay Margate Ramsgate Folkestone Dover Deal Sittingbourne Sheerness
A weathered brick wall with patches of grey plaster and exposed red bricks

Weald and Greensand Belt

Why cracks open in summer and close in winter

Send a description of the cracks you have noticed. A specialist firm will read it and tell you whether the movement needs investigating, at no cost to you.

Get an opinion on your cracks Read about crack grades first

The clay beneath the Weald and the greensand ridge

Inland Kent sits on thick deposits of Weald Clay and Lower Greensand. These soils behave differently from the London Clay found further north. They hold water through the winter and give it up slowly when temperatures rise.

Houses built on these clays rest on ground that changes volume with the seasons. The change is not dramatic enough to feel underfoot, but brickwork and foundations register every millimetre of it. A home near Sevenoaks or Tonbridge experiences this cycle every year without exception.

The greensand belt runs east across the county, passing through towns like Maidstone and Ashford. Where sand meets clay, drainage patterns shift over short distances. Two houses on the same road can sit on entirely different ground behaviour.

How dry summers pull moisture from the soil

Clay shrinks as it dries. During a warm summer, tree roots draw moisture from deep in the soil, and the surface bakes. The ground beneath the foundations contracts.

This shrinkage is rarely even. One corner of a house might sit over a patch of clay that has dried faster than the rest, because a mature oak stands nearby or a drain leaks less on that side. The foundation settles slightly into the space left behind.

Bricks and mortar do not stretch. When one part of a wall drops and another stays put, the tension finds release as a crack. On Wealden clay, this usually happens between June and September, after several weeks without rain. The wider the gap between the wettest and driest months, the more pronounced the movement becomes.

Winter rains and the slow swell back

When autumn arrives, the soil begins absorbing water again. Clay swells as its moisture content rises, pushing gently against the underside of the foundations.

The crack that opened in August may narrow by December. This closing is often taken as proof the problem has gone away. It has not. The clay has simply returned to its winter volume, and the wall has been pushed back toward its original position.

Each cycle leaves traces. Mortar dust falls from the crack edges. Paint fractures along the line. Over several years, the crack may fail to close fully, leaving a permanent gap that grows a fraction wider each summer. Monitoring this pattern tells a structural engineer whether the movement is stable or getting worse.

Trees, drains and the speed of drying

Not every house on Wealden clay moves the same way. Trees accelerate moisture loss. A single mature beech can extract thousands of litres from the soil in a growing season, creating a zone of intense shrinkage around its root spread.

Drains matter too. A leaking pipe adds water to one spot, keeping the clay there soft while the surrounding ground hardens. Blocked gutters pour rainwater against one wall all winter, then leave it dry in summer. Both situations create uneven support.

A specialist surveyor looks at the whole picture: the species and distance of nearby trees, the age and condition of below-ground drainage, and the depth of the foundations. Houses built before modern regulations often have shallow footings that sit right in the active zone where moisture fluctuates most.

What a movement survey measures on this ground

Knowing that clay shrinks and swells does not tell you what to do about a specific house. A structural movement survey records the direction, width and taper of each crack, mapping how the walls have shifted relative to one another.

On Wealden clay, the surveyor pays attention to seasonal timing. A crack measured in February tells a different story from one measured in September. That is why monitoring over several months produces clearer answers than a single visit.

Crack gauges fixed across the widest gaps record movement week by week. The data shows whether the house is settling back each winter or drifting further out of alignment. Only once that pattern is established can a specialist firm decide if stabilisation work is needed, or if managing the trees and drains is enough.

Signs the ground under your home is moving

Wealden clay expands and contracts with the seasons. That movement transfers into the walls above. These are the things you might notice inside or outside your home as the ground shifts.

  1. 1

    Diagonal cracks near windows

    Lines running at an angle from window corners, often wider at the top. They tend to open in late summer and narrow again after heavy rain.

    Row of traditional brick houses with blue doors
  2. 2

    Doors catching on frames

    A door that sticks in August but swings freely by January suggests the frame has distorted slightly as the wall moved around it.

    Charming and colorful facade of terraced houses in Notting Hill, London.
  3. 3

    Gaps at skirting boards

    A visible space between the skirting and the floor, especially on an exterior wall, can indicate the floor slab has dropped relative to the wall.

    man climbing on ladder inside room
  4. 4

    Cracks reopening after repair

    Filler that splits again within a year points to ongoing movement rather than a one-off settlement event that has already stopped.

    Construction site with houses and heavy machinery
  5. 5

    Rippled wallpaper on one wall

    Paper lifting or creasing along a vertical line often follows a crack forming in the plaster beneath, driven by lateral wall movement.

    Scaffolding set up on an old brick building under restoration, with a flag above.

Questions about clay movement in Kent

Ground conditions vary across the Weald and the greensand belt. Here are the things homeowners ask most often.

Will the cracking stop on its own?
Seasonal movement repeats every year. It stops only if the cause changes, such as removing a tree or fixing a leaking drain.
Does my home need underpinning?
Many cases resolve with drain repairs or tree management. A specialist firm recommends underpinning only when monitoring proves the movement is progressive.
Should I wait until winter?
Measuring cracks at their widest gives the clearest data. A survey in late summer captures the full extent of seasonal movement.
Are older houses more at risk?
Shallow foundations make Victorian and Edwardian homes more vulnerable to clay shrinkage, but any building on Wealden clay can move.
Can resin injection fix this?
Resin firms use injection to firm weak ground. Whether it suits clay shrinkage depends on the depth of movement and the foundation type.

Tell us what you have noticed

Send a brief description of the cracks or movement. A specialist firm will review it and advise whether a survey is warranted. There is no charge for this initial assessment.

  • No obligation
  • Free to enquire
  • Specialist response

What you send goes to one independent subsidence specialist for your area, and that specialist may pay this site once your enquiry has been passed on. There is nothing for you to pay us, you are welcome to seek quotations from other firms too, and our privacy notice has more on where your information goes.