How a tree moves a foundation

Roots don’t push slabs up. That’s the common assumption and it’s almost always wrong. What they do is dry the soil out, and clay that dries out shrinks, and a slab sitting on shrinking clay goes down.

The effect is local, which is exactly what makes it damaging. A tree on the west side of the house dries that side while the north side stays damp. That’s differential movement, and differential movement is what cracks brick and racks door frames. A house drying out evenly on all four sides would drop as a unit and you might never notice.

You can usually see it in the elevation survey before anyone mentions trees. The low corner faces the canopy. It shows up on the same corner in the survey year after year, and it gets worse in drought.

Which trees, and how close

The usual suspects in McKinney are live oak, red oak, bur oak, cedar elm, and cottonwood. Cedar elm in particular is aggressive and everywhere in Collin County. Bradford pears and crape myrtles are rarely a factor.

A rough guide: a tree is worth evaluating if it stands closer to the foundation than its own mature height, and it’s a likely problem if it’s closer than half that. Roots commonly extend two to three times the canopy radius, well past where most people assume they stop. If the branches reach over your roofline, the roots are under your slab.

That said, proximity alone doesn’t convict a tree. Plenty of large oaks sit close to houses in the Historic District and cause nothing, because the soil around them stays consistently moist. It’s the combination — big tree, dry season, no supplemental water — that does damage.

What a root barrier is

A vertical sheet of HDPE, typically 40 to 60 mil, set in a trench between the tree and the foundation. Roots hit it and turn rather than continuing under the house. The soil on your side of the barrier keeps its moisture.

Depth is the part that determines whether it works. In North Texas clay the active moisture zone runs deep, and a barrier that stops at three feet just teaches roots to dive under it. We typically trench eight to ten feet, sometimes deeper depending on the tree and the soil profile. A shallow barrier is money spent on nothing.

Placement is the other part. Too close to the trunk and you sever enough of the root plate to destabilize or kill the tree. Too close to the house and you’re trenching through the zone you’re trying to protect. Generally we set it as near the foundation as we reasonably can while staying clear of the slab edge, plumbing, and irrigation.

Installation runs a day or two for a typical run. Trenching equipment needs access, so gate width and any hardscape in the path affect the plan and the price.

Barrier or remove the tree?

People ask this constantly and the honest answer is that removal is not the automatic win it sounds like.

When a large tree comes out, the soil it had been drying starts rehydrating. Clay that has been in a shrunken state for years swells back, sometimes substantially, and that heave can lift a section of foundation and cause its own damage. It’s slow — the process can run for years — but it’s real, and it’s a known failure mode in expansive soil regions. Removal near a house is a decision worth making with an arborist and, in serious cases, a structural engineer.

A barrier keeps the tree, keeps the shade, keeps the property value, and manages the moisture. In most cases that’s the better trade. Removal makes sense when the tree is already dying, structurally unsound, or so close that no barrier can be placed without wrecking the root plate.

Before removing anything mature, check with the City of McKinney. Tree preservation rules exist here and can apply to larger specimens and to certain properties, and requirements change. Ten minutes on the phone with the city beats finding out afterward.

What a barrier won’t do

• It won’t lift a foundation that has already dropped. That’s piering work.
• It won’t help if the real problem is a plumbing leak or bad drainage. Diagnose first.
• It won’t work at three feet deep. See above.
• It won’t replace watering. Barrier plus a consistent soaker hose schedule is the combination that actually holds moisture steady.
• It won’t protect a side of the house it isn’t installed on.

Root barrier cost in McKinney

Work	Typical range
Root barrier, per linear foot installed	$35 – $80
Typical single-tree run (25–40 ft)	$1,200 – $3,200
Multiple trees or full side of house	$3,000 – $7,000
Combined with drainage in the same trench	Usually cheaper than doing each separately

Price moves with depth, access, and what’s in the trench line. If you’re already having drainage work done on the same side, combining the two saves real money because the excavation happens once.

Back to foundation repair in McKinney.