What Is Subsidence?

Subsidence is the downward movement of the ground supporting a building. When this movement is uneven, it places stress on walls and foundations, leading to visible cracks, sloping floors, or doors and windows that suddenly stick.

Common Causes of Subsidence

One of the most common causes of subsidence in Ireland is clay-rich soil, which is particularly vulnerable because it absorbs water during heavy rainfall and shrinks during drier spells. This repeated shrink-swell action can compromise a building’s foundation over time. Peat soils, which are also widespread in Ireland, can shrink irreversibly when dry, causing severe damage to properties. If you’re unsure about the soil type in your area, you can find out using the Ordnance Survey Ireland’s GeoHive Hub interactive online maps.  

Water-thirsty trees are also a concern, as they draw up water through their roots, leaving the soil drier and more prone to shrinkage. This is an increasing problem in Ireland, particularly in areas of high clay content such as Dublin, Cork and Kilkenny. 

Other common causes of subsidence include:

Seasonal drying – warmer, drier summers, coupled with wetter winters, are becoming more common in Ireland, which is increasing the risk of movement.

Leaking drains – heavy rainfall can overwhelm local drainage systems causing localised flooding and soil movement.

How Trees Contribute to Subsidence

Seasonal moisture variations in clay soil typically occur within the top metre of ground. For older buildings with shallow foundations, this movement alone can cause significant damage. However, where trees are present, they will absorb more water from the ground via their root system. Tree roots can draw moisture from deeper levels, sometimes several metres, meaning even newer homes with deeper foundations are not immune.

A mature oak tree, for example, can absorb around 50 gallons per day. Different species demand different amounts of water, so it’s worth understanding which trees you have nearby to help assess the risk.

Problematic Tree Species in Ireland

Some trees are more likely to cause subsidence than others, thanks to their aggressive roots or high water demand. In some cases, root spread can extend beyond the height of the tree! Below is a list of the worst trees for subsidence common to Ireland, and the recommended safe planting distances.

Ash trees (Fraxinus species)

Ash trees are fast growing with high water demands that can affect soil moisture over a large area. They are common throughout Ireland, often found in hedgerows and woodlands. However, they are currently under threat across the country because of a highly infectious fungal disease (ash dieback).

Conifers (including Leylandii)

Conifers are some of the fastest growing trees, often growing between 2.5-3 feet a year. This species is a popular choice for hedges. However, their high moisture uptake and shallow roots can damage soils, especially near shallow foundations and drains.

Oaks (Quercus species)

Although these grand, majestic trees look impressive, they can pose a significant risk to foundations if they are too close to homes. Their extensive, shallow root system spread far from the trunk and consume high quantities of water. The Irish Oak (Sessile Oak) can grow up to 40m in height. 

Poplars (Populus species)

These tall, rapidly growing trees have an invasive root system that can extend aggressively in search of water and affect nearby foundations. Poplars are known to cause significant soil shrinkage and are often responsible for foundation cracks and heave after removal.

Willows (Salix species)

Weeping willows are extremely thirsty. Willow tree roots can extend up to 40m in search of water, which is why they’re typically planted near lakesides and riverbanks. If planted near homes, they can cause significant foundation issues.

Signs of Tree-Related Subsidence

Tree-related subsidence often develops gradually, but early warning signs can help homeowners act before damage becomes severe. The symptoms are similar to general subsidence but tend to appear more quickly during warm, dry periods when trees take more moisture from the soil.

Common Symptoms

Tree-related ground movement can show subtle signs before becoming an issue. Watch for these early warning signs around your property:

• Diagonal cracks in brickwork or plaster, often wider at the top

• Doors and windows sticking due to slight movement in the building’s frame

• Sloping or uneven floors that worsen during dry summer months

• Visible tree roots near walls, paths, or driveways

• Ground sinking near large, high water-demand trees

Monitoring and Early Detection of Tree-Related Subsidence

Regularly check your property during dry spells, particularly if you have fast-growing or water-hungry species nearby. You should avoid removing large trees suddenly, as this may trigger ground heave. If you notice cracks, sticking doors or other symptoms, you can seek advice from a specialist who can confirm whether tree roots are contributing to the problem and recommend appropriate next steps.

How to Prevent and Manage Tree-Related Subsidence

If you intend to plant trees, you should avoid planting them close to properties, especially if they are located on clay or peat soils. If you already have trees in the vicinity of your home, there are several ways to manage the risk of tree-related subsidence.

Tree Management Strategies

Large, mature trees can often be managed rather than removed. Techniques such as pollarding or crown thinning carried out by a qualified arborist can reduce water uptake by limiting the amount of foliage. Even simply replacing high water-demand trees with lower water-demand demanding trees can help reduce the risk.

In cases where the tree needs to remain, root barriers can provide an effective solution. Root barriers are specially designed membranes made from heavy-duty plastic, copper, or engineered fabric, installed underground to prevent root intrusion. To ensure best results, they should be installed by a ground engineering expert such as Mainmark Ireland.

Structural and Ground Solutions

If a property has already suffered from ground movement, modern remediation technologies can restore the ground's stability and level structures with minimal disruption. Mainmark Ireland uses innovative methods such as resin injection and screw piling, which provide a faster, cleaner, and less invasive alternative to traditional underpinning.

Address the Root of the Problem

Although trees bring a touch of beauty, shade and biodiversity to our gardens, some species can pose a risk to foundations if planted too close to a property. Understanding the types of trees you have, monitoring signs of movement, and managing high-risk species proactively can help prevent significant costs and damage.

If you’re worried about tree roots affecting your home or have noticed early signs of subsidence, contact Mainmark Ireland today who can assess your property, diagnose the issue and provide tailored recommendations to fix the issue.