Removing a tree is sometimes necessary, for example, if it has become diseased or unsafe, or if you want to use the land for a different purpose. However, it can be problematic for the foundations of a property due to the ground becoming uneven. This is known as ground heave and can result in damage to landscaping or even walkways or driveways. Read on to find out how to prevent ground heave when removing a tree.
What is ground heave?
Ground heave can occur when a tree is removed from the soil. Since the water is longer able to be absorbed by the tree’s roots, the soil begins to swell as it gets wet. This swelling can lead to the soil lifting up, sometimes to a greater volume than when the property was constructed. This can cause the foundations to shift. The amount of heave that occurs after tree removal depends on a number of factors, including the age of the tree, the permeability of the soil and the availability of free water.
Tree heave is most likely to occur if the tree was older and had a very high water demand, such as poplar, oak and willow. It can be difficult to say how long it’ll take for the ground to recover from tree heave. Whilst sometimes it can take as little as a few months, it could possibly take as long as 25 years to return to normal.
The key point is that shrinkable clay soil is particularly important when assessing heave risk. Clay soils can change volume as their moisture content changes. If tree roots have caused substantial drying over a long period, removing the tree can allow the soil to rehydrate and swell.
By contrast, non-shrinkable soils such as many sandy or gravelly soils do not behave in the same way. This means the risk cannot be determined simply by looking at the size of the tree.
Ground heave vs subsidence
It is also useful to understand the difference between subsidence and heave.
Subsidence occurs when shrinkable soil loses moisture and contracts, potentially causing downward movement of foundations.
Heave is effectively the opposite process. Previously dried and shrunken soil takes up moisture and expands, potentially causing upward movement.
Trees can therefore be involved in both processes, depending on what is happening to the soil and vegetation.
How to reduce the effects of tree heave
Fortunately, there are things you can do to mitigate the effects of ground heave after tree removal. These include:
- Consider the risk of heave where an existing tree might mature or die. If a tree is planted within the area you’re building on, there’s a good chance that it could die during the building’s lifecycle. This is particularly likely if the tree has dried the soil before the foundations are laid. To combat the issue of soil swelling from existing trees, you could opt to sever the roots so that the soil is able to rehydrate.
- Establish the correct foundation depth for the ground conditions. There are tools available to calculate the depth required for the foundations, taking into account the proximity of the tree and the type of soil. Foundations with a depth of more than 2.5m will need an assessment carried out by an expert.
- Opt for stump removal. Having the stump removed along with the tree will reduce the number of roots remaining in the ground, reducing the risk of heave occurring.
What increases the risk of ground heave after tree removal?
There is no single factor that determines whether heave will occur. A proper assessment considers the site as a whole.
A professional assessment may therefore need information about the soil, foundations, tree and surrounding vegetation before removal is recommended.
How to reduce the effects of tree heave
Fortunately, there are things you can do to mitigate the effects of ground heave after tree removal. These include:
Consider the risk of heave where an existing tree might mature or die
If a tree is planted within the area you’re building on, there’s a good chance that it could die during the building’s lifecycle. This is particularly likely if the tree has dried the soil before the foundations are laid. To combat the issue of soil swelling from existing trees, you could opt to sever the roots so that the soil is able to rehydrate.
For new developments, the relationship between existing trees, soil conditions and proposed foundations should be considered at the design stage. Current guidance for development near trees requires consideration of potential indirect damage from subsidence and heave.
Establish the correct foundation depth for the ground conditions
Establish the correct foundation depth for the ground conditions. There are tools available to calculate the depth required for the foundations, taking into account the proximity of the tree and the type of soil. Foundations with a depth of more than 2.5m will need an assessment carried out by an expert.
Foundation design is ultimately a matter for the appropriate structural and geotechnical professionals. Where trees are close to proposed buildings, an arboricultural assessment and appropriate foundation design should be considered together.
Opt for stump removal
Removal of the stump along with the tree can reduce the amount of living root material remaining in the ground. However, stump removal should not be viewed as a guaranteed way of preventing ground heave.
The roots responsible for soil drying may extend well beyond the stump, so simply grinding or excavating the stump does not automatically eliminate the possibility of soil movement.
ADVICE
If you have a mature tree close to a property, particularly where shrinkable clay soil or previous subsidence is suspected, seek professional advice before arranging removal.
Can ground heave be fixed?
If you have a ground heave after tree removal, it’s best to contact experienced professionals to help. Sometimes, the solution can be simply to pump water out of the area that’s causing the problem. However, occasionally the affected area might need to be excavated and broken pipes repaired or replaced. A qualified professional will be able to identify the cause of the ground heave and work to address it effectively.
If you notice cracking, movement or other potential signs of structural damage, contact your building insurer and consider obtaining appropriate advice from a structural engineer or building surveyor. Councils commonly recommend that suspected tree-related subsidence or heave is investigated using appropriate technical evidence rather than assuming that a tree is responsible.
If you need tree removal and want to reduce the risk of ground heave, contact experienced tree surgeons to carry out the work. Get in touch with Essex Tree Brothers by calling 0800 or by sending us a message via the website contact form.
ETB TIP
Don’t assume removing a tree will cause ground heave. The risk depends on the soil, tree, foundations and whether the ground has previously been significantly dried by the tree.
What should you do before removing a tree near your property?
If you have a mature tree close to a house, extension, garage or other structure, don’t make the decision based on the tree alone.
Consider:
1. Have the tree assessed
An arborist can assess the species, size, condition, location and likely management requirements.
2. Consider the soil
If shrinkable clay is suspected, the potential for soil movement may need further investigation.
3. Look at the building
Consider the type, age and depth of the foundations, particularly if the tree predates the building.
4. Check for previous movement
Existing or historic cracking and evidence of subsidence may be relevant when assessing potential heave.
5. Check drainage
Leaking drains can alter soil moisture and may contribute to ground movement.
6. Check whether the tree is protected
Before carrying out tree work, establish whether a Tree Preservation Order or conservation area controls the tree.
For concerns about the health or condition of a tree before deciding whether removal is necessary, you may also find our guide useful: Is There Something Wrong With My Tree?
Professional Tree Removal in Essex
If you need tree removal and want to reduce the risk of ground heave, contact experienced tree surgeons to carry out the work. Get in touch with Essex Tree Brothers by calling 0800 059 0176 or by sending us a message via the website.
Essex Tree Brothers provides professional tree surgery and tree felling services across Essex. Our experienced team can assess your tree, discuss your requirements and explain the most appropriate approach before work begins.
Our experienced team can assess your tree and discuss the safest and most appropriate approach to tree removal.
GET EXPERT ADVICESpecies with high water demand, including oak, willow and poplar, can have a significant influence on soil moisture. However, species alone does not determine heave risk. Soil conditions, tree size, distance from foundations and previous soil drying also need to be considered.
There is no fixed timeframe. Soil moisture and volume can change over an extended period, and the duration depends on the site conditions. If structural movement is suspected, professional investigation is recommended rather than relying on a standard timeframe.
Not necessarily. Stump removal reduces the remaining stump and root material, but roots can extend considerably beyond the stump. Removing the stump therefore does not guarantee that heave will be prevented.
Potentially. If previously desiccated shrinkable clay rehydrates and expands, it can cause ground movement that affects foundations. However, other causes of building movement should also be investigated before attributing damage to tree removal.
Yes. If you believe your property is experiencing subsidence or heave, contacting your building insurer is an important first step. Your insurer can arrange appropriate investigations and advise on the claims process.
