Heave Damage Repair in Liverpool

What is heave, and how is it different from subsidence?

Subsidence is the ground beneath the foundations moving down. Heave is the opposite: the ground pushes up. Both are commonly linked to shrinkable clay soils, which change volume with their moisture content. The NHBC Standards describe how clay that dries out shrinks, which can cause subsidence, and clay that rewets swells, which can cause heave.

The difference matters because the treatment can be very different. A repair that suits subsidence, such as removing a source of drying, could make heave worse, and underpinning ground that is still swelling can simply transfer the uplift into the new foundations. That is why heave is a job for diagnosis first and building work second.

Crack patterns are only a clue, not a diagnosis. The engineer looks at the whole building, the ground and its history before deciding which is happening.

What causes heave around Liverpool homes?

Parts of Merseyside sit on glacial clay, and where that clay has had a large thirsty tree growing in it for decades, the ground around the roots can be permanently drier than it would otherwise be. If the tree is removed, the clay slowly takes water back up and expands. The NHBC lists oak, poplar, willow, elm, hawthorn and eucalyptus among the high water-demand species, so felling one of those close to a house on clay is a recognised heave risk.

• Tree removalA mature tree felled near the house, or a tall hedge grubbed out, letting the clay recover its moisture.
• Leaking drains or water pipesA long-running leak saturating clay beneath part of a floor or wall.
• Building on dried-out groundAn extension built where a tree once stood, on foundations that did not allow for the clay swelling back.
• Ground-bearing floorsSolid floors laid directly on clay can be lifted even when the walls are not.

Because felling a large tree on clay can lead to heave, tree work near a building should follow advice from an arboriculturist and the structural engineer. Trees covered by a Tree Preservation Order, or in a conservation area, also need the council’s consent or notice first, so check with your council before anything is cut.

What are the signs of heave damage?

The signs overlap with subsidence, which is why people often assume the wrong thing. Common ones include:

• cracks that are wider at the bottom than at the top;
• solid ground floors that have risen, cracked or developed a hump, sometimes with skirting boards lifting;
• doors catching at the top of the frame or no longer closing;
• cracks appearing some months or years after a large tree was removed nearby;
• a new extension pulling away from the original house at the junction.

If floors are lifting, our floor repair page covers how failed ground-bearing slabs are dealt with, and junction cracks on newer additions are covered under extension subsidence repair.

How is heave investigated?

Heave can carry on for a long time after its trigger, so the first question is whether the ground is still moving. The engineer will usually want:

1. History. When cracks first appeared, whether any trees or hedges were removed and when, and whether there have been leaks.
2. Site investigation. Trial pits or boreholes to see the foundations and the soil, with samples tested for moisture and plasticity. Our soil and site investigation page explains what this involves.
3. Drain checks. A CCTV drain survey if a leak could be adding water to the ground.
4. Monitoring. Level and crack monitoring over a period, often around a year, to see whether the building is still rising.
5. Diagnosis. The engineer interprets all of this and decides whether repair can go ahead now or should wait for the ground to settle down.

How is heave damage repaired?

There is no single heave repair. Once the engineer is satisfied about the cause and the state of the ground, options can include:

• Waiting and repairing cosmetically where movement has stopped and damage is minor;
• replacing a lifted ground-bearing floor with a suspended floor designed to leave a void or compressible layer for the clay to swell into;
• deeper foundations such as mini-piled underpinning, designed with heave precautions so uplift on the piles and beams is allowed for;
• repairing cracked masonry once movement has stopped, for example with crack stitching.

Whatever is chosen, we build it to the engineer’s design, with Building Control involved where the Building Regulations apply, and party wall procedures considered if the work is close to a neighbour.

What affects the cost of a heave repair?

We do not give prices before the engineer’s design, because heave schemes vary enormously. The cost depends on how long investigation and monitoring take, whether only floors or also walls are affected, the depth to stable ground, the method, access, drain and tree advice, party wall and Building Control involvement, and how much internal making-good follows. The underpinning cost guide sets out published national figures for underpinning work.

Where we see heave enquiries

We cover all of Liverpool and Merseyside. Heave questions tend to come from homes with large gardens and mature trees close to the house, which is common in suburbs such as Allerton, Mossley Hill and Woolton, but any property near a recently removed tree or a long-term leak can be affected. Heave work is part of our wider foundation repair and underpinning in Liverpool.