Experts in Concrete Patio root remediation

How to Deal with Tree Roots Lifting a Patio Slab

Tree roots venturing under a patio slab can cause uneven surfaces, cracked concrete, and even safety hazards. Left unchecked, these roots can continue to grow and escalate damage over time.

In this in-depth guide, we uncover why tree roots invade patio bases, how to safely remove or redirect them, and the best repair techniques to restore structural integrity, and prevent future disruption.

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Why Tree Roots Lift Patio Slabs

Patio slabs are vulnerable to root intrusion, especially from mature trees nearby. Understanding the root behaviours and the conditions that encourage them can help in planning a long-term solution.

Roots Seek Moisture and Nutrients

Tree roots naturally grow under pavement in search of water and nutrients. Even small gaps in the patio bedding layer can be enough for roots to squeeze in, leading to progressive lifting and cracking as they thicken and swell.

Type of Tree Matters

Fast-growing species such as silver birch, willow, poplar, and maple have aggressive root systems. These roots can spread widely and lift slabs significantly within just a few growing seasons if left unchecked.

Shallow Root Patterns

Some trees develop shallow roots that spread just below the surface, directly beneath patio slabs. These are especially damaging because they apply upward pressure precisely where the slab is unsupported, causing localized lifting and cracking.

Tight Sub-base Encourages Surface Roots

A compacted sub-base might restrict deeper root growth, forcing roots to grow laterally and uplift instead. Moisture pooling due to poor drainage exacerbates the issue, creating ideal conditions for root invasion under patios.

Slow The Damage with Early Action

Small root intrusion may be unnoticeable at first. Acting early to prune or redirect roots can prevent major slab lifting. Delayed action can lead to slabs becoming uneven, cracked, or unsafe underfoot.

Effective Repair and Prevention Methods

Root-Prune and Re-Level

Expose the root by carefully lifting the affected slab.
Cut the root back beyond the slab edge using proper tools and consider stopper treatment (root barrier).
Re-compact the base, re-bed and level the slab with fresh mortar or concrete mix.

Install Root Barrier

Use a vertical root barrier of at least 600 mm deep between the tree and patio.
This limits horizontal root growth and protects the patio area.
Re-lay slabs and monitor annually to ensure roots stay clear.

Relocate or Remove the Tree (If Necessary)

For large root systems causing irreparable damage, consider tree removal or transplanting.
Obtain necessary permissions, especially for protected species or large trees.
After removal, replace base material and lay a fresh sub-base before re-installing patio slabs.

Frequently Asked Questions

You can prune the offending root, but it's essential to remove the lifted slab and re-level the base. Simply chopping without relaying will allow the root to regrow and cause uplift again.

No – root barriers are designed to redirect roots without harming the tree. They encourage deeper descent rather than lateral spread beneath patios.

A barrier should be at least 600 mm deep or extend below the root flare to intercept major roots. It must run continuously along the patio border.

Not always. If root invasion is localised and the tree is healthy, pruning and a barrier may be sufficient. But extensive root spreads may require removal or relocation.

Yes, especially for large or protected trees. An arborist can safely prune roots without harming the tree’s stability and structure.