Trees near buildings: how close is too close, and what insurers expect

There is no fixed safe distance between a tree and a house, and most trees cause no damage, but soil type, foundation depth and the tree's thirst all affect the risk.

For homeowners in Leicestershire and across the East Midlands, there is no single safe distance for trees near buildings, and the great majority of trees never cause any damage. The RHS advice on trees near buildings explains that the real questions are how thirsty the tree is, what kind of soil the house stands on and how deep its foundations go. Where all three point the wrong way, a tree can contribute to subsidence. Where they don’t, a large tree close to a house may be no trouble at all.

This guide covers which homes are most at risk, what cracks may and may not mean, who is responsible if a tree is blamed and what you can sensibly do about it. For most property owners the picture is reassuring. Keep healthy trees, know the signs worth watching for, and act when there is evidence.

How close a tree can be to a house

Distance tells you very little on its own. The RHS says tree roots can spread up to three times the height of the tree, so a 10m tree could have roots reaching 30m from the trunk. That figure can sound worrying, but the zone that matters for subsidence is much smaller. Subsidence is the ground sinking beneath a building’s foundations. It happens when a tree draws enough water out of the soil to dry it and make it shrink.

How far that drying reaches depends on the species. For high water demand species, the RHS expects the drying influence to reach outwards a distance equal to tree height. For intermediate and low water demand species, it is unlikely to reach more than half tree height.

Take a 10m tree as a worked example. If it is a high water demand species, it may dry the soil up to 10m away. A 10m tree with low or intermediate water demand is unlikely to have any drying effect beyond 5m. The two trees are the same size, yet the area where they might affect a house is very different. A house 7m away would sit inside the first zone and outside the second.

Oak (Quercus) accounts for the highest number of subsidence cases in the UK. That does not make every oak near a house a problem, and a large oak on stable ground or beside a modern house may never cause any trouble. It simply means oak is a species where the soil and the building deserve a closer look.

Which homes are most at risk of subsidence

The RHS says tree-related subsidence is generally only a problem on shrinkable clay soils. Clay shrinks as it dries and swells again when it gets wet, and the damage is worst in dry years. Gravels, sands and other soils that don’t shrink in the same way are far less of a concern.

The soil is driest in late summer. Experts call this a “seasonal soil moisture deficit”, meaning the shortfall in water that builds up over the growing season. It is seasonal because the soil normally rewets once the winter rains arrive, so the ground moves down in summer and recovers in winter.

The age of the building counts for a great deal. Buildings of up to four storeys built before the 1950s are most at risk, because they frequently have comparatively shallow foundations. Building Regulations came in during the 1970s, so most houses built after 1980 have deeper footings and are much less likely to be damaged by nearby trees.

Here is how those figures fit together. A two-storey house built in the 1930s on shrinkable clay, with a high water demand tree standing closer than its own height, is the kind of combination where problems can arise. The same tree beside a house built in the 1990s would usually be far less of a concern, because the deeper footings sit below the soil the tree is drying.

Extensions are more vulnerable to subsidence than the main house. If you are planning one on clay soil, get advice from a structural engineer before you start.

Roots, drains, paving and sheds

Many people worry that roots will push through their foundations. The RHS says roots are unlikely to penetrate sound footings directly. Roots grow towards water, so they get into drains where water is available, and watertight drains generally have no trouble from them.

Older drains with poor seals and rigid joints are the most likely to let roots in. A leaking drain can also wash away soil and leave cavities in the ground around it. The RHS gives three options for a leaking old drain. It can be lined with a resin-soaked liner, or replaced with polypropylene drainage pipes, which is the most permanent fix. Removing the tree is the last resort, since the leak is the underlying fault.

Above ground, suckers (shoots that grow up from the roots) and expanding roots can lift paving and lightweight structures such as sheds and garages. They cannot lift heavier structures. Most of this lifting happens within a 1m radius of the trunk, so a patio laid right up to a tree is far more likely to move than one set a few metres away. Cherries (Prunus) have roots close to the surface and are more likely than most trees to lift paving. If a path or patio is lifting, the large roots close to the tree should not be cut. A tree surgeon can suggest other ways to deal with the surface.

Root barriers may look like a neat answer. They work in theory, but they usually cannot be installed deep enough, and roots may simply grow underneath them.

Spotting cracks and what they could mean

Cracks caused by soil movement are most likely around windows and doors. Usually 5-10mm of movement is needed before cracks develop, so fine hairline marks elsewhere in a wall are not necessarily a sign of subsidence.

Timing is a useful clue. Cracks that appear in late summer are most likely to be linked to trees or other vegetation, because that is when the seasonal deficit peaks. Cracks that appear at other times of year are more likely to have another cause.

Working out the cause properly takes time. The RHS says level monitoring, which means measuring whether parts of the building rise and fall over the seasons, is more reliable than soil investigation or root identification for deciding responsibility. Crack monitoring should only be done alongside it. The RHS does not offer a root identification service.

Because ways of predicting tree damage are largely fallible, the RHS view is that it is normally best to wait until a tree causes damage before taking action. We think this is sound advice. Felling a healthy tree “just in case” can mean losing shade, privacy and wildlife for a problem that may never happen. If cracks do appear, tell your building insurer. They will investigate and inform the tree owner of any remedial action that is needed.

Who is liable when a tree damages a house

A tree belongs to the owner of the land it grows on, and that owner is responsible for it. If the tree is “materially contributing” to damage to a building, the owner may be liable for the full cost of repairs. The RHS lists several arguments that will not work as a defence: that the tree was there before the building, that the building’s foundations were inadequate, that the tree is worth more than the building, or that the owner was unaware of the risk.

Possible defences are that the tree was managed appropriately, that the clay soil could not reasonably have been foreseen, or that no remedial action was available that would have prevented the damage. Keeping a record of sensible tree management may help an owner later.

If you are told that your tree may be damaging a neighbour’s property, the RHS sets out three steps. Tell your contents insurer, as this falls under third party liability cover. Read the reports carefully, as you are entitled to full disclosure of them. Then take prompt remedial action if it is appropriate.

The rule also works the other way. A neighbour cannot be forced to fell a tree unless there is evidence of damage to the house and evidence that their tree is to blame. Conifer hedges are different and may qualify for reduction under the High Hedges Act.

Before any work on a tree, check with your Local Planning Authority whether a Tree Preservation Order (TPO) applies. A protected tree, including one in a Conservation Area, can still be required to be felled if it is damaging buildings. Applications usually need monitoring, investigations and reports first.

Pruning, felling and the risk of heave

Many owners hope a trim will solve the problem. To make any difference to subsidence, pruning has to reduce crown volume by at least 70 percent and be repeated regularly, for example every three years. That is a heavy, ongoing commitment that changes the look of a tree considerably. Crown thinning (removing selected branches to let light through) does not reduce the amount of water the tree uses, so it will not help with subsidence.

Where a tree is the main cause of subsidence, felling is usually the most permanent solution. There is one exception. Some soils have a permanent moisture deficit, meaning they stay dried out from one year to the next and never fully rewet over winter. London clay is an example. Felling on these soils risks progressive heave, where the ground swells as it slowly takes up water again and pushes the building upwards. In those cases, underpinning with full anti-heave precautions may be the only effective answer. Heave is rare, and it is much less common in the UK now because most of the houses at risk have already been underpinned.

Trees are not the only plants that dry the soil. Large wall shrubs, notably Pyracantha and Wisteria, can cause subsidence in a small area. Tall hedges can also add to soil drying. In subsidence-prone spots, the RHS suggests keeping a hedge no taller than its distance from the building, so a hedge 3m from the house should be kept at 3m or less.

The right course for any one tree depends on its species, the soil and the history of the building, which is why hard pruning and safe removal decisions are best made with a qualified arborist.

What it means for your property

Trees and houses sit side by side safely in most gardens, and where trouble does arise there is a clear process to follow, from insurers and monitoring through to pruning, drain repairs or felling. The message is simple: find out whether your house sits on clay and roughly when it was built, watch for cracks around windows and doors in late summer and tell your insurer if any appear, and get a proper assessment before pruning hard or felling. The same practical principles apply to the trees in your own garden, along your boundaries or on your smallholding. If you’d like an arborist to look at a tree that concerns you, the Harbour Tree Care team is happy to help.