Tree roots are lifting my patio — what can I do?

A root lifting paving is doing what roots do: growing radially in the top 300mm of soil, and thickening year on year. Paving laid on a thin bed over that zone will always be lifted eventually. The tree is not going to stop, so the useful question is how to make the surface tolerant rather than how to stop the root, and that reframing solves most of these problems.

What you'll need

• A spade and a trowel
• Bolster and lump hammer (optional)
• Sharp sand and aggregate
• Gravel or bark (optional)
• Timber for a raised deck (optional)

Step by step

1. Understand what you are looking at first.Lift a slab and look. A large woody root running under the paving is structural and important to the tree. A mat of fine roots is not, and can be pruned with far less consequence.
2. Do not cut major roots.As a rough guide, cutting roots thicker than about 25 to 50mm, or cutting any root close to the trunk, risks both destabilising the tree and creating an entry point for decay. Roots within roughly three to five trunk diameters of the base are the anchoring ones and should not be cut at all. If in doubt, ask an arboriculturist before sawing anything.
3. Check whether the tree is protected.Root severance can count as damaging a protected tree. A TPO or Conservation Area status means checking with the council before doing anything to roots as well as branches.
4. Consider lifting and relaying over a flexible build-up.Take the slabs up, remove and replace only the fine roots, lay a geotextile membrane, and rebuild with a thicker sand or grit bed and open joints, or convert to block paving laid on sand. Flexible construction accommodates a few millimetres of movement without cracking, which rigid mortar cannot.
5. Raise the level rather than digging down.Building the surface up over the root — with a thicker sub-base, a slight ramp, or a step — avoids cutting anything. Do not add deep soil over the whole root plate; a localised build-up in the paved area is different from burying the root zone.
6. Reroute the path.Often the cheapest and best answer. Curving a path around the root zone looks better than a straight one, costs less than repeated repairs, and removes the conflict permanently.
7. Change the surface to something forgiving.Gravel over a membrane, bark, resin-bound aggregate on a flexible base, or a timber deck on adjustable pedestals will all follow root movement instead of fighting it. A deck spanning over roots is the classic solution around a mature tree and looks deliberate.
8. Deal with the trip hazard immediately, whatever the long-term plan.Lifted slabs are a genuine hazard and a liability if a visitor falls. Grind, ramp or temporarily remove the lifted edge now, and plan the proper repair separately.
9. Prune roots only as a last resort, and get advice.If a root really must be reduced, an arboriculturist can advise on where and how much, ideally cutting cleanly at a distance from the trunk and only on one side, and often combined with crown reduction to rebalance the tree. It is never a job to do on both sides in one year.
10. Think about the tree's future.If the tree is young and badly sited, moving or replacing it now is far cheaper than twenty years of paving repairs. If it is mature and valuable, redesign the surface around it.

Tips

• The area right around a mature tree is the worst possible place for rigid paving. Mulch, gravel or a deck there and pave further out.
• A permeable surface over a root zone also lets the tree get water and air, which paving denies it. Both parties benefit.
• Photograph the roots before you cover them again. It is useful if the question of tree stability comes up later.

Common mistakes

• Sawing through the root to fix the slab — Large roots anchor the tree and feed it. Cutting them can cause instability that shows up years later in a storm, and creates a decay pathway into the base of the trunk.
• Relaying slabs on a full mortar bed over the same root — Rigid construction cracks with the first millimetre of movement. Flexible construction is the whole point.
• Concreting over the root zone — It suffocates roots, kills the tree slowly, and the concrete cracks anyway.
• Cutting roots on both sides of a tree in the same year — It removes anchorage symmetrically and is the fastest way to make a tree unstable.

If it doesn't work

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