Both subsidence and heave are a type of ground movement that can have serious consequences for your home if left untreated.
But what’s the difference between heave and subsidence?
Heave is the upward movement of the ground beneath a property which can happen when the soil expands. Subsidence is the opposite of heave and occurs when the ground beneath a property’s foundation sinks downwards without any imposed load. Both subsidence and heave can affect the structural integrity of your home.
Like subsidence, signs of heave should not be ignored.
In this article we’ll look at the causes and signs of heave to enable you to recognise the signs and act fast. We also look at whether your home insurance policy will cover any damage caused to your home by heave.
If your property is suffering from subsidence or heave but you want to sell, you can use the free quiz below to help determine the best way forward
1. Is heave the same as subsidence?
Heave is not the same as subsidence. Heave happens when the ground beneath your home rises upwards because the soil is saturated and expands. Subsidence has the opposite effect and occurs when the ground beneath your home sinks downwards.
Although heave and subsidence cause the ground to move in opposite directions, a lot of their signs and symptoms are the same.
2. Why does ground heave occur?
Heave occurs when the soil beneath your home’s foundation expands upwards.
Heave most commonly takes place in shrinkable soils (aka “cohesive soils”) such as clay and silt. When cohesive soils absorb large quantities of water, the soil will swell and increase in volume. These swelling pressures are what cause the foundations of your home to lift, or “heave”, in places.
According to ProHort, the measure of ground movement for heave is “relatively small (less than 150mm)”. However, this can have a dramatic effect on the structural integrity of your home.
2.1 What causes ground heave?
The most common cause of ground heave is the removal or death of nearby trees.
Trees extract large quantities of water from the soil through their root systems each day. According to The Association of British Insurers (ABI), a mature deciduous tree can remove in excess of 50,000 litres per year!
When a tree is removed, the moisture that was once absorbed through the tree’s root system instead is retained by the soil and gradually builds up over time. This causes the clay-rich soils to swell and expand upwards.
Heave is particularly likely to occur if the tree was:
- Mature and established, especially if the tree pre-dated the house.
- Had a high water demand, such as the thirsty willow, poplar and oak tree.
While removed or dead trees can cause heave, living trees can cause another type of ground movement: subsidence. Read more about how trees can cause subsidence in my article “Subsidence: The 6 Biggest Causes & How To Reduce The Risk”.
Other causes of ground heave include:
- Removal of soil during excavation.
- Change in the level of the water table.
- Extreme weather conditions, such as flooding.
- Freezing (and subsequent expanding) of trapped water in the ground.
- Nearby building works affecting ground drainage.
- Water escaping through broken drains and damaged pipes.
If your house is built on non-cohesive soil, a burst pipe is likely to have the opposite effect. The water can wash away the fine particles below the foundation of your home and can ultimately cause subsidence if parts of the foundation are left with no support.
2.2 What type of soil is my house built on?
Ground heave is most likely to occur in cohesive soils, such as clay and silt. This is because cohesive soils can absorb large quantities of water and expand in volume when saturated.
Clay soil is most commonly found in the South East of England.
If you want to find out what type of soil your home is built on, you can use the BGS’ Geology Viewer. Click on the search icon on the top right of the page, enter your postcode or location and then click on the map to bring up the bedrock geology.
We searched for Clapham Park in the above example, which has a bedrock geology of “London Clay Formation” made up of clay and silt.
3. What are the signs of heave
The signs of ground heave are:
- Vertical cracks in walls, brickwork and windows. Like subsidence, heave can cause cracks to appear in your property. However, cracks caused by heave tend to be vertical, while subsidence cracks are often diagonal in shape.
- Sticking doors and windows. You may also notice that your doors and windows start to stick and become difficult to operate. This can also be a sign of subsidence.
- Lifting of patios, driveways and paths surrounding your home. Keep an eye on your driveway and any patios and paths that surround your house. If any of them begin to lift at the corners, it could be a sign of heave.
4. Is ground heave covered by insurance?
Heave is covered by most home insurance policies, provided your property has not had problems with heave in the past. You will have to pay a higher excess when you make a claim for heave. Most policies have an excess of around £1,000 for these types of claims, but the exact amount will be set out in your policy.
A good home insurance policy should cover you for:
- Cost of the repair, up to the sum insured under the buildings cover of your policy.
- Alternative accommodation if the work needed to repair the damage means your home is uninhabitable.
- Damage to surrounding structures (e.g., your patio), but this is usually only included if the damage occurred at the same time and by the same cause as the damage to the property.
- Loss or damage to contents if the loss or damage was caused by ground heave.
Make sure you review your insurance policy, so you understand what is covered and what is excluded.
If in doubt, contact your insurer to clarify your excess for this type of claim and any exclusions that may apply.
5. How long does it take for heave to occur?
Ground heave can take many years to progress and show any signs of damage.
A lot will depend on what is causing the damage. A burst pipe is likely to saturate the soil beneath your property a lot faster than soil finding a new equilibrium after a tree has died or been removed.
In the case of tree removal, Peter Barry from Peter Barry Chartered Surveyors states that “heave is likely to be progressive, as the clay will take up moisture following tree removal until it finds a new equilibrium. This can result in upward movement of foundations over a number of years”.
It is good to be aware of the causes and signs of heave, so you can act quickly if you suspect your home could be suffering from any form of ground movement. A structural engineer will be able to carry out tests to confirm if your property is suffering from heave.
6. What is worse heave or subsidence?
Generally, the damage caused by heave is often much more severe than that caused by subsidence. The damage, the cost and how long it will take to fix will vary though on a case by case basis.
On the other hand, subsidence is much more common than heave. So, you are probably more likely to experience subsidence as a homeowner.
Both subsidence and heave can significantly affect a property’s value. In both cases, it pays to act fast, get to the root of the problem and prevent any further damage.
7. What should you do if you suspect ground heave?
If you spot signs of heave, make sure you inform your insurer as soon as possible. It’s best to be proactive as problems left untreated can result in more extreme, time consuming and expensive repairs.
Your insurer will arrange for a structural engineer to visit your property and accurately diagnose the issue. They may need to carry out further tests, such as soil analysis, to be able to pinpoint the cause of the heave.
You should expect to pay around £700-£1,000 for a professional structural survey. The cost will be covered by your insurance, but your excess for a heave claim is likely to be about the same amount.
Once the final report has been filed, most insurers will then arrange for any necessary repairs to be carried out by their approved contractors.
8. Can you sell a house with heave?
The good news is that you can sell a house with heave, but it can be much harder and take a lot longer than selling a “problem-free property”.
If you are struggling to sell your house the traditional estate agency route, for many, selling by auction will be the best solution. I designed the free quiz below to help you determine the best way to sell your property if it's suffering from subsidence or heave.
It can offer a faster and more certain sale and potentially a better selling price. Auctioneers have considerably more experience selling problem properties than estate agents.
The audience will also be better suited to problem properties, as it’s common to find experienced investors, builders and cash buyers at auction looking for a “fixer-upper”.
If you think selling by auction could be right for you, make sure you check out “My Guide To Finding The Best Auction House In The UK”.
By Matthew Cooper, Co-Founder of Home Selling Expert