A dry summer is over, the rain is back, and you have noticed cracks that were not there in spring. You may be hoping they will close up on their own. Sometimes they partly do, but often not quickly, and the worst thing you can do is fill them before anyone has understood what they are doing.
Key Takeaways
- Cracks that appear after a dry summer can come from clay soil shrinking under shallow foundations, but that is not the only cause. Around Huddersfield the ground is generally less shrinkable than the clays of south-east England, and clay is one of several suspects.
- Where clay shrinkage is the cause, autumn rain does not reverse it quickly. The ground can take more than one winter to recover.
- The most useful question is whether a crack is seasonal (partly closing in winter and reopening in summer), static, or getting steadily worse. One measurement on one day cannot answer it.
- Do not fill and redecorate yet. Filling removes the evidence of how wide the crack was and whether it has changed.
- Do not fell a nearby tree without advice. Do check your buildings insurance policy, since most expect you to tell the insurer as soon as you reasonably can about damage that could lead to a claim, and do check gutters and drains near the cracking. Some signs, such as rapid widening or bulging brickwork, need advice straight away rather than monitoring.
Two Misconceptions Pulling in Opposite Directions
The first misconception is that a crack appearing in August means the house is falling down. The second is that the first heavy autumn rain will put it right. Both can be wrong, and the second is the more expensive mistake. It persuades people to fill cracks and redecorate before anyone has understood what those cracks are doing, and that removes the evidence that would have guided a sensible decision.
This post is written from general engineering principles, not from a single case. The mechanisms below are well understood. Which one applies to your house is the part that needs someone to look.
What Might Be Happening Under Your House
Some clay soils change volume as their moisture content changes. Through a dry summer the ground dries out, the clay shrinks, and a shallow foundation on it can move down, usually unevenly. That is one form of subsidence: ground movement that the building moves with. It is different from settlement, the initial bedding-down of a new building under its own weight, and from heave, the ground swelling upward as clay takes up water again.
Trees and large shrubs make it worse. A mature tree in leaf draws a great deal of water from the ground, from a zone that can reach well beyond the edge of its canopy. The species, its mature height, and its distance from the house all matter. NHBC Standards Chapter 4.2, on building near trees, is the guidance used for new foundations on clay near trees, and it is the reason those foundations go deeper than they otherwise would.
Foundation depth largely decides the outcome. Seasonal drying is greatest in the upper part of the ground, and it reaches deeper near trees. A foundation below the zone that dries out is largely unaffected by a dry summer. A shallow footing, common in older houses, may not be. That is why two neighbouring houses on the same ground can behave quite differently in a hot, dry year.
Around Huddersfield, Clay Is Only One Suspect
Much of the advice about summer cracking is written with the highly shrinkable clays of south-east England in mind. The ground around Huddersfield is different. It is mostly mudstones and sandstones of the Coal Measures and the Millstone Grit, in places with a covering of glacial till or of weathered material that has crept down the slopes. Weathered mudstone and till can be clay-rich and can shrink, but usually less than the southern clays. Less is not none.
So a crack that appeared this summer here could be clay shrinkage, but it could also come from a leaking drain or gutter softening the ground, from made or filled ground (old quarries, mill ponds, and hillside plots levelled with fill are common here), from a slope or retained ground on a hillside plot, from old coal mine workings, or from a problem in the wall itself such as a failed lintel. The timing of a crack is a clue, not an answer. That is why an engineer will usually look at the drains, the slope, and the mining records as well as the trees.
Not every crack that appears at this time of year comes from the ground. Walls expand in hot weather and contract as it cools, and when the heating goes on in autumn, plaster and timber dry out and shrink. Fine cracks at ceiling and wall junctions, or along plasterboard joints, are often no more than that.
Why the Rain Does Not Fix It Quickly
Where clay has dried out over several months, it does not recover in a weekend. Heavy rain after a long dry spell tends to run off hard, dry ground rather than soak in, and the water that does soak in moves down slowly. Recovery is measured in months, and after a very dry year it can take more than one winter.
In practice, cracks that opened in July or August may still be open, or only a little narrower, by November. On its own that is not evidence that something serious is happening. The question is whether the cracking is seasonal, static, or getting worse, and one observation cannot tell you.
Seasonal, Static, or Getting Worse
Cracking caused by seasonal ground movement often partly closes over winter and reopens the following summer. That pattern tells you something that a single crack width does not. It points to a building responding to the seasons: a problem that can become costly if it is ignored for years, but a different kind of problem from movement that keeps going.
Cracking that widens steadily, never closes between seasons, and comes with doors and windows that increasingly stick or floors that go out of level is telling a different story. That needs earlier professional advice.
This is why monitoring over at least one full seasonal cycle is so useful. A single reading tells you a crack exists. A series of readings, taken with a proper crack gauge and recorded with the date and the width each time, tells you whether it is seasonal, static, or getting worse.
Some signs should not wait for a season of monitoring. If a crack is widening quickly, brickwork or stone is bulging or loose, or a door or window has jammed at the same time as new or widening cracks appear around it, get advice straight away. If you think part of the building could fall, keep people clear of it and get a structural engineer out urgently. If it could fall onto a road, a path, or a neighbour’s property, also tell your council’s building control team, which deals with dangerous structures. If a hole or sudden hollow opens in the ground, keep people away from it. If it could be linked to old coal mine workings, or you are not sure, report it to the Mining Remediation Authority (formerly the Coal Authority) at once.
What I Look At When I Assess Cracking
When I attend a property to look at cracking, I am not just looking at the width. Several things together build the picture.
Direction and pattern. Diagonal and stepped cracks through brick or stone, often running from the corners of windows and doors, are what movement in the ground below typically produces, although a failed lintel or thermal movement can produce similar cracks. Openings are the weak points in a wall, so that is where cracks tend to appear.
Taper. Whether a crack is wider at the top or the bottom helps show which way that part of the wall has moved.
Distribution. Whether cracking is inside, outside, or both, and whether it all points to one area of movement or is scattered, all help the interpretation.
Other signs. Doors and windows that stick, floors that are out of level, and gaps opening at skirtings or cornices help confirm whether the cracks match real movement of the structure. Bear in mind that timber doors and windows often stick in damp autumn weather anyway, so a door that has only just started to stick tells you less than one that has got steadily worse.
BRE Digest 251, Assessment of damage in low-rise buildings, gives the classification engineers use to grade how severe damage is, from damage that is only cosmetic to damage that affects how the building works or its stability. Grading it properly needs measurement and context. A photograph posted online cannot do it.
Three Things Not to Do, and Two to Check
- Do not fill and redecorate yet. Fresh filler removes the baseline. If a crack later reopens through new filler, you have lost the record of when it started, how wide it was, and whether it has changed. If you need to fill a crack for weather-tightness, photograph it first with a ruler held against it, and write down the date.
- Do not fell a mature tree close to the house without advice. A tree that has been drawing water from clay for decades has reached a balance with the ground. Remove it suddenly and the clay can take up water and swell, and that heave can cause more damage than the shrinkage did. Trees covered by a Tree Preservation Order need the council’s consent for most work, and trees in a conservation area need notice to the council before work, so check with the council before any work to the tree. If the tree is not on your land, speak to its owner rather than acting yourself. Removing a tree before anyone has looked also removes evidence an investigation may need.
- Do not rely on the rain to settle the question. Record the cracks now, with dated photographs and measurements, so there is something to compare against next spring and next summer.
- Do check your buildings insurance policy. Most policies expect you to tell the insurer as soon as you reasonably can about damage that could lead to a claim, and delay can cause problems later. Check your policy wording for the exact condition, or ask your insurer or broker. Your insurer may appoint its own loss adjuster or engineer, and may monitor the cracks for some months before deciding what to do. If old coal mine workings could be involved, the Mining Remediation Authority has its own subsidence claims process, which is separate from your insurance. You can contact them as well as your insurer.
- Do check your gutters, downpipes, and drains near the cracking. An overflowing gutter, a downpipe spilling onto the ground, or a blocked gully next to the wall is usually cheap to put right, and water soaking into the ground beside a wall can soften it and let it move. If you suspect a broken drain, a drainage contractor can survey it with a camera. Tell your insurer before any repair, as the survey may form part of a claim.
When to Get a Structural Engineer
If cracking is getting wider, runs diagonally through the wall and shows both inside and out, or comes with floors going out of level, gaps opening at junctions, or doors and windows that are getting steadily worse, get it looked at by a chartered structural engineer before you fill it or make any changes. The same applies if there is a large tree close to the house. A fine crack in plaster only, with none of these signs, can usually be recorded and watched. You do not always need a full investigation straight away. Sometimes a visit and a period of monitoring is the right first step. What you need is someone who can tell you which kind of problem you have.
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I am a Chartered Structural Engineer (CEng, MIStructE) based in Huddersfield. The Beam Doctor offers homeowners and builders:
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