When a tree root lifts a slab, cracks a driveway, or pushes against a foundation, the instinct is to grab a saw and cut the root out. That instinct can be an expensive mistake. A large root like the one in this photo is often a structural root, one of the few that hold the tree up and carry its water, and cutting it in the wrong place can leave the tree unstable, invite decay, or kill it outright, turning a cracked slab into a failed tree over your roof. I am Christopher Hodge, an ISA Board Certified Master Arborist, and this page explains what tree roots do to property, and why the first step is not cutting the root but identifying the tree it belongs to.
What tree roots do to foundations and hardscape
Tree roots grow where the water, the air, and the loose soil are, and that is often right along the edge of a slab, a footing, or a foundation. As a root grows in diameter it acts like a slow wedge. It can lift and crack concrete flatwork, patios, driveways, and sidewalks, heave pavers, and push against foundation walls and footings. Roots rarely break through a sound, deep foundation on their own, but they can widen cracks that are already there, disturb shallow footings, and, on the expansive clay soils common in our foothills, worsen the soil movement that damages foundations. They also find their way into cracked or leaking sewer and drain lines, which is the root intrusion that plumbers deal with.
Before you cut a large root, identify the tree
This is the step almost everyone skips. Before any large root is cut, you need to know which tree it comes from and what that tree can tolerate. Trace the root back to its trunk. A root's size, its position, and its distance from the trunk tell you whether it is a structural root the tree depends on for stability or a minor one that can be pruned safely. Species matters just as much. A deep rooted oak responds very differently from a shallow, aggressive poplar, cottonwood, willow, or elm, the kinds of trees most often behind a lifted slab. Cutting a major structural root close to the trunk can remove a large share of the tree's anchorage and its water supply, and the tree may fail in the next windstorm or decline over the following seasons. The right question is not only how do I stop the damage, but what will this cut do to the tree.
Root pruning done right, or removal when it is the only option
Once the tree and the offending root are identified, there are usually options short of losing the tree. Proper root pruning cuts the root cleanly, at a distance from the trunk that the species and the tree's condition can tolerate, often followed by a root barrier that redirects future growth away from the structure. Sometimes repairing the hardscape with more root room, a root deflector, or a slightly relocated path solves the problem without touching a major root at all. But sometimes the honest answer is that the tree is too close, too large, or too dependent on the very roots doing the damage, and removal is the only mitigation that actually protects the structure. Because I run no removal crews, I have no reason to push you toward a removal you do not need, or away from one you do.
How I assess root and property conflicts
I come to the site, trace the roots back to the tree, identify the species, and assess the tree's health and structure along with the damage to the slab, footing, or foundation. Then I give you a written assessment with the realistic options: what can be root pruned and how far from the trunk, whether a root barrier or a hardscape change will hold, and whether removal is warranted. If the damage involves the house foundation itself, I will tell you when a structural engineer should also weigh in. You get a clear, independent recommendation you can act on or hand to a contractor.
Frequently Asked Questions
Can tree roots damage a house foundation?
They can, though usually indirectly. Roots seldom punch through a sound, deep foundation, but they can widen cracks that already exist, disturb shallow footings and slabs, and, in expansive clay soils, worsen the shrinking and swelling that cracks foundations. Far more often, roots damage the flatwork around a house, the driveways, patios, walkways, and slabs, by lifting and cracking them as they grow.
Can I just cut the root that is lifting my concrete?
Not without knowing what you are cutting. A large root can be a structural root that anchors the tree, and cutting it close to the trunk can make the tree unstable or kill it. Trace the root back to the tree first. An arborist can tell you whether that specific root can be pruned safely, how far from the trunk the cut should be, and whether a root barrier will keep it from returning, or whether removal is the safer answer.
Which trees most often damage concrete and foundations?
Fast growing, shallow rooted, water loving species are the usual offenders: poplars and cottonwoods, willows, silver maple, and some elms. Oaks and other deep rooted trees can still lift hardscape when they are planted too close, but they are less aggressive about it. Identifying the species is part of deciding what can be done, because each one tolerates root pruning differently.
Do you remove the tree, or fix the roots?
I do neither directly. I am an independent consulting arborist, so I diagnose the conflict and write the recommendation, whether that is root pruning at a safe distance, a root barrier, a hardscape change, or removal, and you hire the crew or contractor to carry it out. That independence is the point: my advice is based on the tree and the structure, not on selling the work. Call or text (530) 391-6100.
Will a root barrier stop tree roots from coming back?
A root barrier can help, but it is not a cure on its own. Installed correctly, a barrier redirects new root growth down and away from a slab, foundation, or pipe, and it works best when it goes in before the damage is severe or is paired with a clean root pruning cut. It will not undo damage already done, and a barrier placed too shallow or too close to a large tree can simply be overgrown. Whether a barrier is the right tool depends on the tree, the soil, and how close the roots already are, which is what I assess before recommending one.
Sources
- International Society of Arboriculture best management practices on root management and tree stability, and standard arboricultural guidance on structural roots and root pruning distances.