Heave vs Subsidence: Why Removing a Tree Can Lift a House
Subsidence takes a building down. Heave pushes it up, and it is usually the same clay doing both. Here is what heave is, why felling the wrong tree causes it, how long it lasts, and what an engineer does about it.
In short: heave is the ground swelling upwards beneath a building. In the UK it almost always means shrinkable clay taking water back after something that had been drying it, usually a tree, is removed, dies or is cut hard back. It is the reverse of subsidence, and the damage looks similar in reverse: tapered cracks, sticking doors, floors that lift instead of dip. How long it lasts depends on how deeply the tree had dried the ground: a year or two where the clay was rewetting each winter, many years where a deep dry zone had built up over decades, with swelling of up to 100 to 150 mm in a high-shrinkage clay. That is why an engineer checks for a persistent moisture deficit before anyone fells a mature tree next to a house, and why the fix for serious heave is underpinning designed to resist uplift, not a cheaper alternative.
What heave is, and what causes it
Heave is upward movement of the site caused by the soil expanding. Clay is the only common soil that does this to any degree, because water in clay is bonded to the surface of the particles rather than sitting in the spaces between them; add water and the particles push apart, take it away and they pull together. The volume change is real: a building imposes only 20 to 40 kN/m² on the ground through a strip footing and settles a firm clay by a few millimetres, but the suction a drying clay develops is in the hundreds of kN/m², so shrinkage and swelling can move the ground by 100 mm or more. Much of London sits on London Clay, one of the more shrinkable clays in the country, which is why both subsidence and heave are London problems.
The triggers, in order of how often we see them:
- A tree removed, dead or heavily pruned. By far the most common. The tree had been drawing water out of the clay every summer, the clay had shrunk, and once the demand stops the ground rewets and swells. A storm-felled tree, a hedge grubbed out, a large tree killed by disease or a neighbour's clearance all count.
- Water into dried clay. A long-term leak from a drain or water main, or a new path or extension that changes where rainwater goes, can rewet clay that had been persistently dry under a tree, producing local heave.
- Unloading. Excavating a basement or a deep cutting removes weight from the clay, which slowly swells into the space; basement designs allow for it.
- Frost. Freezing water expands. In the UK frost rarely penetrates more than half a metre, so it mainly affects unheated buildings and shallow footings.
- Chemical heave. A different mechanism: sulphates in old hardcore beneath a ground floor slab react with the concrete and expand, lifting the slab and sometimes the walls on it. London Clay itself is sulphate-bearing, which is why underpinning concrete here is specified sulphate-resisting.
Insurance claims for heave are rare compared with subsidence, but when heave happens it is often more expensive to resolve, because the movement can go on for years and there is no cheap way to stop it.
Seasonal or persistent: the question that decides everything
Whether removing a tree causes a short recovery or years of heave depends on the state the tree had left the clay in. Tree roots draw far more water out in summer than rain puts back, and deciduous trees take almost nothing in winter, so the ground beneath a tree cycles: drying and shrinking through the summer, rewetting and swelling through the winter. In many gardens the clay returns to its natural moisture content, its "field capacity", by every spring. That is a seasonal deficit. Remove the tree and the following winter's recovery is simply the last one, complete within a year or two, sometimes by the next spring if the tree was felled in autumn. A house that had been dropping a little each summer comes back up to where it started and the cracks often close.
Where the clay has low permeability and the tree has been drying it to depth for many years, the winter rain cannot get all the way down. A zone of dry clay develops under and around the tree that never fully rewets, deepening and widening as the tree grows. That is a persistent deficit, and it is what the high-demand species, oak, poplar, willow, elm and the cypress family, create on clay. Remove the tree and the ground starts a long, slow rehydration that can take many years, more than twenty in extreme cases, with the rate falling off over time. If the house was built after the tree had already dried the ground, which is common with old street trees and newer infill houses, the swelling lifts the building above the level it was built at, and the damage is worse than the subsidence would ever have been.
How much the ground can move
The amount of swelling depends on how shrinkable the clay is, which a laboratory measures as its plasticity index and grades as low, medium or high volume change potential, and on how deep and how dry the deficit zone had become. As a broad guide:
| Clay volume change potential | Possible swelling after rehydration | What it means for a house |
|---|---|---|
| Low | Up to around 50 mm | Noticeable cracking where movement is uneven |
| Medium | Up to around 100 mm | Serious cracking, doors and floors affected |
| High (much of London Clay) | Up to around 150 mm | Structural damage; anti-heave underpinning is usually the remedy |
Indicative upper figures for a deep, persistent moisture deficit rehydrating fully. Actual movement depends on the depth of drying, the permeability of the clay and the foundations; it must be assessed for the site.
The pressure behind that swelling is typically more than 100 kN/m², which comfortably exceeds the weight a house puts on its footings. The clay does not care that there is a building in the way.
What heave damage looks like
Heave produces the subsidence crack pattern in reverse, and the reversal is the clue. Subsidence cracks are tapered, widest at a free edge, and because a corner has dropped they are typically diagonal and widest at the top. Heave cracks are also tapered and also start at a corner or an opening, but they can be much nearer vertical, and where a corner has risen they are often widest lower down, sometimes at the damp-proof course. Because the part of the building nearest the old tree is rising, the distortion is the mirror image of what the same tree would have caused while alive, and since many heaving houses had earlier subsidence cracks repointed, the two patterns can overlap and confuse the picture.
Other signs: doors and windows that begin to stick, ground-bearing floor slabs that dome or lift at the edge nearest the tree, skirting boards parting from a lifted floor, and a history that fits, a large tree or hedge removed, blown over or dead in the last few years, or a leak into ground that had been dry. Our guides to the signs of subsidence and to types of cracks cover the reading of cracks in more detail.
How an engineer confirms heave
The diagnosis rests on three things. First, level monitoring: brass or stainless markers around the building read with a precise level every six to eight weeks. Subsidence from a live tree goes down in summer and part-way back up in winter; a leaking drain goes steadily down; heave goes steadily up, at a rate that slowly declines. A few readings over the right months usually settle it. Second, the ground itself: trial pits and hand-auger boreholes with moisture content measured every 200 to 250 mm down the profile, compared with the clay's liquid limit and with a borehole away from the old tree; where the moisture is well below what the clay would hold at field capacity, and the deficit runs deep, the swelling has further to go. Soil suction testing is the most reliable measure of desiccation, and the most expensive. Third, the roots: dead roots persist in the ground for years after felling and can be identified to species, which ties the movement to the tree that was removed. Our site investigation team carries out the pits and sampling for the engineer.
What can be done about it
The first thing to know is what cannot be done: there is no practical way to hold a clay at the moisture content where it neither shrinks nor swells, and no proven system for managing ground moisture around a house. The choice is therefore between waiting and building.
Where the investigation shows a shallow, seasonal deficit, the swelling is short-lived and often helpful, closing the cracks that the tree caused. The sensible course is to monitor through at least one winter and summer, then repair the cracks and redecorate once the readings are flat, using crack stitching and repointing as part of an engineering-led repair. Repairing early wastes the money, because the cracks reopen.
Where a deep persistent deficit is rehydrating and the movement is unacceptable, the building has to be carried past the swelling clay. That means underpinning, but not the ordinary kind. Mass concrete pins in swelling clay simply get lifted with everything else. Anti-heave underpinning uses mini-piles taken down below the zone that is rewetting, designed to resist the uplift the clay will exert on their shafts, with a sleeve or slip liner over their upper length to reduce that grip; ground beams that sit on a compressible void former so the clay can rise beneath them without touching the structure; and, where there is a ground-bearing slab, a new suspended floor with a void below it. The existing footings are isolated from the new structure so they cannot transmit the lift. It is a designed solution with Building Regulations approval and a Certificate of Structural Adequacy at the end, and it is the one case where underpinning is chosen because the ground is going up.
Before you touch a tree
Most heave is self-inflicted, by an owner, a neighbour or a contractor removing a tree that was quietly holding the ground in a state everyone had got used to. Three rules avoid most of it. Where a tree is implicated in subsidence, the first remedy is crown reduction by an arboriculturist, repeated every two to three years, because it reduces the tree's water demand without the shock of felling; crown thinning does not work and is no longer recommended. Where felling is proposed, have the ground investigated first for a persistent deficit, and if one exists, accept that underpinning with anti-heave measures may be part of the plan, tree or no tree. And check with the council before any work, because a tree with a preservation order or in a conservation area cannot be touched, roots included, without consent. Our guide to trees and subsidence sets out the prune, fell or underpin decision in full, and our guide to foundations near trees on clay covers which species matter and how far their influence reaches.
Building on land where trees have been removed
The same physics governs new foundations. On a clay site where trees were cleared shortly before construction, the ground beneath is still swelling, so the standard approach is to design as though the tree were still there and add heave precautions: piles rather than trenches, ground beams on a void former, a suspended ground floor with a gap beneath it, and compressible material against the sides of any deep element. A tree removed within about a year of the foundations being laid is treated as present for design purposes, and where a persistent deficit is suspected the period is longer. Getting this wrong on an extension is a common source of cracking at the junction with the existing house, which stands on older, shallower footings that are moving differently.
Heave and your insurance
Most UK buildings policies cover damage from subsidence, heave or landslip of the site in the same clause, so heave is an insured peril, subject to the usual conditions and exclusions. Two are worth noting. The policy expects you to maintain the property, and removing or hard-pruning a large tree near the house without advice can be argued to be the opposite. And the excess, the exclusions for paths, drives and floor slabs, and the twelve months or more that investigation takes are the same as for subsidence; our guide to subsidence insurance claims explains the process, and our repair cost guide covers what each stage costs.
Where EMA Structures fits
We diagnose heave the same way we diagnose subsidence, by evidence, in stages, each priced before it starts. The subsidence assessment, £495 to £895 + VAT depending on the size of the property and the type of movement, covers the inspection, a record of every crack, a level survey, a diagnosis and a written report. Level and crack monitoring is £1,200 to £2,000 + VAT for the set-up and three seasonal visits, £350 + VAT per further visit. Trial pits, soil moisture and suction testing and root identification are not included in those fees; they are quoted separately once the assessment shows they are needed, and our specialist site team carries out the pits. Where the answer is to wait, we say so and specify the repairs for when the ground has settled. Where it is anti-heave underpinning, we design it, obtain the approvals, deliver it through our specialist construction arm or oversee it, and issue the Certificate of Structural Adequacy. Start with a subsidence assessment, or send us photographs of the cracks and a note of any trees that have gone.
Figures in this article are typical values for UK clay soils and are indicative only; the movement, timescale and remedy for any property depend on its ground, foundations and history and must be assessed by a structural engineer. Fees correct as of September 2026, excluding VAT.
Heave questions
What is heave?
Heave is the upward movement of the ground beneath part or all of a building as the soil expands. In the UK it almost always means shrinkable clay taking water back and swelling after something that had been drying it, usually a tree, is removed, dies or is heavily cut back. Frost, a long-term leak into dried clay and the removal of load by excavation can cause it too, and a chemically driven version lifts ground floor slabs laid on sulphate-rich hardcore. Heave is the opposite of subsidence and can crack a building just as badly.
What is the difference between heave and subsidence?
Direction and cause. Subsidence is the ground losing volume or support and the building dropping, most often clay shrinking as trees and dry summers draw water out of it, or a leaking drain softening or washing out the ground. Heave is the ground gaining volume and the building lifting, most often the same clay swelling back once the tree is gone. Both produce tapered cracks that are widest at a free edge, but subsidence cracks are typically widest at the top and diagonal, while heave cracks can be nearer vertical and widest lower down, and level monitoring shows one going steadily down and the other going up at a diminishing rate.
How long does heave last after a tree is cut down?
It depends on whether the tree had built up a persistent dry zone. If the clay was rewetting fully each winter, removing the tree just extends the normal seasonal recovery and the swelling is usually finished within a year or two, sometimes by the following spring. If the tree had dried the clay deeply over decades, the ground can go on taking water up and swelling for many years, in extreme cases more than twenty, with the rate slowing over time. In a high-shrinkage clay the total swell can reach 100 to 150 mm.
Can heave be fixed?
Yes, but not by adjusting the moisture in the ground; there is no practical way to balance a clay between shrinking and swelling. Where the swelling is short-lived, the answer is to monitor until it stops and then repair the cracks. Where a deep persistent dry zone is rehydrating and the movement is unacceptable, the building is underpinned with anti-heave measures: piles taken below the swelling zone and designed to resist the uplift, sleeved in their upper length, with ground beams sitting on a compressible void former and any ground floor rebuilt as a suspended slab, so the clay can swell without lifting the structure.
Is heave covered by home insurance?
Most UK buildings policies cover damage caused by subsidence, heave or landslip of the site, and heave claims are rare compared with subsidence. The usual conditions apply: notify promptly, and maintain the property, which includes not removing or heavily pruning a tree near the house without advice. Damage to paths, drives and garden walls on their own, and to ground-bearing floor slabs unless the walls are damaged at the same time, is usually excluded. Wordings differ, so check your own policy.
Should I cut down a tree near my house to prevent subsidence?
Not without an engineer's and an arboriculturist's view. If the tree has been drying the clay for years, felling it can trigger heave that goes on for longer and costs more to fix than the subsidence you were trying to prevent, and a tree that predates the house can lift it above the level it was built at. Crown reduction repeated every two to three years controls a tree's water uptake without that risk. If the tree is protected by a preservation order or stands in a conservation area, you need the council's consent before any work, including to the roots.
What are the signs of heave?
Cracks that taper and run from a corner or an opening, often closer to vertical than subsidence cracks and sometimes widest towards the bottom; doors and windows that begin to stick; a ground floor slab that domes or lifts; skirtings lifting away from a suspended floor; and a history that fits, typically a large tree or hedge removed, felled by a storm or killed in the last few years, or a leaking drain in ground that had been dry. Level monitoring over a few months confirms it: the affected part of the building is going up, at a rate that slowly declines.
A tree gone and cracks appearing?
Send us photos of the cracks and tell us what was removed and when. We will say honestly whether it looks like heave and what the sensible next step is.