You've got a maple out front that's older than the house. One sidewalk panel has been creeping up a little more every year. Now that edge catches the snowblower, the mail carrier's toe, and every bike tire that rolls over it.
You don't want to lose the tree. You don't want to pay for a full tear-out either.
Here's how to think through it.
Step 1: Make Sure It's Actually the Roots
In northeast Wisconsin, roots aren't the only thing that shoves concrete upward. Frost heave does it too: wet soil under a slab freezes, expands, and pushes the concrete up from below.
They need different fixes, so it's worth two minutes to tell them apart:
| Clue | Probably roots | Probably frost heave |
|---|---|---|
| Is there a tree nearby? | Yes, and roots can reach well past the edge of the branches | Doesn't matter |
| Does it change with the seasons? | No. It only gets worse, slowly, year after year | Worst in late winter, then drops back some in spring |
| Where's the rise? | One edge or corner, usually the side facing the tree | Often a whole panel, near downspouts, low spots, or wet areas |
| What does the slab look like? | A hump or a crack running right over the root | Rocking, shifting, cracks that open and close |
If it looks like frost heave, the real problem is water under the slab. That's a drainage conversation first, then a lifting conversation.
If it looks like roots, keep reading.
Step 2: Know What Lifting Can (and Can't) Do
Polyurethane foam lifting, also called polyjacking, works from underneath. We drill a few 5/8" holes (about the size of a dime), inject a high-density structural foam that expands and hardens under the slab, and raise the concrete in small, controlled increments.
Notice the word raise. Foam only goes up.
With root heave, the problem slab is already too high. So the fix flips: we lift the lower slabs on either side to meet the high one, stretching that sharp lip out into a gradual slope you can walk on, shovel over, and roll a stroller across.
Whether that works on your concrete comes down to two things:
- 1How far the slab has been pushedA small to moderate rise can be blended out across the neighboring panels. A slab shoved up several inches, tipped on edge, or snapped in half usually can't be. The slope you'd need would be worse than what you started with.
- 2What the concrete is forThat's the next step.
Step 3: Match the Fix to the Area
| Area | Good candidate for lifting? | Why |
|---|---|---|
| Public sidewalk / front walk | ✅ Usually | The goal is no trip edge. A gentle hump is fine because people are walking on it, not setting furniture on it. |
| Side yard & backyard walkways | ✅ Usually | Same logic as the front walk. |
| Driveway | ⚠️ Sometimes | Depends where the heave is. A rise near the street can often be blended out. A hump in the middle of where you park may bug you. Water still has to drain. |
| Garage approach | ⚠️ Rarely | It has to meet the garage floor and shed water away from the door. There's very little room to build a slope. |
| Patio / pool deck | ❌ Usually not | You want it flat for furniture and drainage. Trading a lip for a hump isn't a real fix. |
Fastest way to find out: Snap two photos. One wide shot that shows the tree and the whole walk, and one close-up of the raised edge with a tape measure standing next to it. Send them over and we can usually tell you from the photos alone whether it's a lifting job.
Your Options, Side by Side
| Option | What it fixes | The catch | Best for |
|---|---|---|---|
| Foam lift the surrounding slabs | The trip hazard and the look | Leaves a gentle hump; roots can keep pushing over time | Sidewalks and walkways with a moderate rise |
| Grind the edge down | Small trip lips | Only works on smaller offsets, leaves a visible ground edge, doesn't stop the root | Minor lips on otherwise flat concrete |
| Prune the root + install a root barrier | Future heaving | Doesn't fix the edge you have today; can hurt or kill the tree if done wrong | Pairing with lifting or replacement |
| Tear out and repour | Everything, if done right | Most expensive and messiest; heavy equipment can damage the tree; new concrete over cut roots can settle later | Severe heave, broken slabs, patios |
| Remove the tree | The cause | You lose the tree, and the rotting roots can leave voids that make concrete sink later (more on that below) | Dead, dying, or badly placed trees |
Dealing With the Roots Themselves
Lifting fixes the concrete, not the tree. If the root keeps growing, the slab can keep rising. Before anyone starts cutting:
- Get an arborist to look at it first. Cutting a big structural root too close to the trunk can destabilize the tree or kill it outright. An ISA Certified Arborist can tell you which roots are safe to prune and which ones the tree is standing on.
- Root barriers steer roots down, not out. They're rigid panels installed in a narrow trench between the tree and the concrete. They work best paired with careful pruning.
- Call Diggers Hotline before you trench. Wisconsin law (Statute 182.0175) requires everyone, homeowners included, to contact Diggers Hotline at least three working days before digging. Dial 811. It's free, and the utilities mark their buried lines for you.
- Check whose tree it is. If the tree is in the terrace (the grass strip between the sidewalk and the street), it may belong to your city or village, not you. Call before cutting any roots, and while you're at it, ask who's responsible for the sidewalk. In a lot of Wisconsin communities, that falls on the homeowner.
And if the root wins again in a few years? Re-lifting a section costs a small fraction of replacing it.
The Tree-Removal Trap (Especially With Ash Trees)
Emerald ash borer has taken out a lot of ash trees across northeast Wisconsin, and plenty of homeowners have had them cut down.
Here's what most people don't expect: removing the tree stops the heaving, but the root system stays in the ground and slowly rots. As it breaks down, it leaves voids under nearby concrete. Slabs that used to get pushed up start sinking down.
The same thing happens after a stump grind. If a tree came down near your driveway or walk in the last few years and you're now seeing settling, cracking, or a slab that rocks when you step on it, that's exactly what foam lifting is built for. The foam fills those voids as it lifts.
Why We Use Foam Instead of Mudjacking
Mudjacking (pumping a heavy cement slurry under the slab) is the old-school way to lift concrete. For root-disturbed soil, foam has real advantages:
- Smaller holes. Dime-sized instead of the much larger holes mudjacking needs.
- Much lighter. Lifting foam weighs a few pounds per cubic foot. Mudjack slurry is in the neighborhood of 100. Piling heavy fill onto soft, root-disturbed soil is a good way to end up with a slab that settles again.
- Won't wash out. Cured foam is waterproof, so spring melt and heavy rain don't erode it.
- Fast. Walk on it right away. Drive on it the same day.