So, you’ve got a known drain line issue under your slab foundation—and now you’re hearing something about “under-slab tunneling.” What the heck does that mean? Is it expensive? Will it mess up your house? Do you even have to do this?
At Anchor Foundation Repair, under-slab tunneling is one of the main services we offer. We know everyone doesn’t know *everything* about what we do, especially when it’s something you’ve never needed for your home before. Don’t worry, we’ll skip the industry jargon and make sure you understand the basic idea of under-slab tunneling from your perspective.
This article walks you through exactly what under-slab tunneling is, how it’s done, how much it costs, and when it actually makes sense for your home.
What Do You Mean by “Under-Slab Tunnel”?
Under-slab tunneling is a repair method used to fix broken or leaking drain lines underneath a concrete slab foundation. It involves digging a tunnel under the home from the outside, rather than breaking through floors inside the house. This gives plumbers access to the problem area without disturbing your interior living space.
The goal is to get to the damaged drain line(s) in a way that avoids tearing up flooring, moving furniture, or covering everything in dust. Once the tunnel is dug and the repair is made by your plumber, the tunnel is carefully filled back in and cleaned up.
You can find more details on the benefits of tunneling here: What Is and Why Use Under-Slab Tunneling for Leaks Under a Foundation?
How Do You Make An Under-Slab Tunnel?
It might sound like a big job—and it is—but the digging process is actually very controlled and methodical. Here’s how we do it at Anchor Foundation Repair:
First, a licensed plumber performs a hydrostatic plumbing test to identify exactly where the drain line is leaking or broken. Knowing the location helps us figure out the best route to dig the tunnel.
Next, we choose the best spot to begin digging. This is somewhere along the outside edge of your foundation. We dig what’s called a “start hole” next to the slab to reach under the concrete beam and begin tunneling horizontally toward the broken pipe.
Once we’ve tunneled far enough to reach the problem area, we notify the plumber so they can make the needed repair. After that, we hand-fill the tunnel with dirt, mud-pump with slurry to stabilize the area, and then backfill the start hole.
BTW, not every company mud-pumps their tunnels, but we do because we believe it’s the best way to secure your home after tunneling.
The work ends with a cleanup of the area so your yard doesn’t look like a disaster zone. For a little more detail, you can check out this article: How Does Under-Slab Tunneling Work? Basic 5-Step Process.
How Much Does Tunneling Cost and How Long Does It Take?
Cost and time are probably the biggest questions on your mind—and we don’t blame you. Here’s a general idea of what to expect.
Typical Under-Slab Tunneling Costs
If you’re using Anchor, under-slab tunneling typically costs around $400 per foot of tunnel and the price per foot goes up with longer tunnels, plus about $650 for each start hole that we dig. The final price depends on how far we need to dig to reach the drain line failure and how many access points are needed.
You can dive deeper into this topic and get more general price ranges across the industry here: (2025 Version) What’s The Price for Under-Slab Tunneling?
Tunneling Timelines
The total time it takes can vary depending on how long the tunnel is and what kind of soil you’re dealing with. But here’s a typical breakdown:
- Digging and Tunneling: 1 to 4 days
- Plumbing Repairs: Usually 1 day
- Backfilling and Mud-Pumping: 1 to 3 days
So from start to finish, you’re likely looking at 3 to 8 working days to get everything done. For more detail on tunneling timelines, check this out: How Long Does an Under-Slab Tunneling Project Take from Start to Finish?
How Much of a Mess Is Tunneling Going to Be?
You might be imagining a big muddy mess in your home—but with under-slab tunneling, that’s not the case. In fact, one of the main reasons homeowners choose tunneling is to avoid the mess that comes with tearing up the inside of the house.
With under-slab tunneling, there’s no need to break through your floors, remove tile or carpet, or worry about dust and debris inside. Your furniture stays in place, your floors remain untouched, and your daily life doesn’t get turned upside down. Doesn’t that sound way better than the alternative of breaking through your slab (which can be a total chaos zone)??
The only real mess to expect is a pile or two of dirt in the yard or maybe the driveway. We do our best to keep those piles as tidy as possible, and everything gets cleaned up when the job is done.
Do I Need to Do Tunneling? Is It Necessary?
This is where you have to weigh your options. Under-slab tunneling isn’t always required, but in many cases, it’s the smartest way to fix a serious problem without temporarily turning your home’s interior into a disaster zone.
Here are some important things to ask yourself before making a decision:
Can I Afford Tunneling?
Tunneling isn’t cheap, so budget matters. If your plumbing repair is small and easy to access from inside, you might decide it’s not worth the extra cost. But if insurance is covering some or all of the tunneling expenses, that can make it a lot more manageable.
Do I Want or Am I Okay With a Mess Inside My Home?
If the repair could be done from inside but that would mean ripping up your floors and living in a dusty, noisy mess for days, tunneling might feel like a much better option.
It’s all about what kind of disruption you’re willing to live with or if you can relocate easily during the work.
Will Insurance Be Helping Out With the Tunneling Costs?
In some cases, insurance may help pay for the tunneling but not for tearing up your floors. That kind of coverage detail can make a big difference in the decision-making process. Check your policy or talk with your insurance adjuster to find out what’s covered.
Do I Know the Exact Location of the Failure?
If the plumber has confirmed exactly where the leak is—and there’s only one that’s not far from the edge of the home—tunneling might not be needed. But if there are multiple leaks or a section of pipe needs to be replaced entirely, the job becomes more complex and costly but also more necessary to handle with tunneling. You’ll want to know the full picture before deciding.
Is There a Possibility of Degrading Cast Iron Lines?
Homes built with older and now degrading cast iron drain lines are more likely to have widespread issues. If you’re in an aging cast iron situation, a one-off repair might not be enough. Tunneling can allow for full replacement of all the lines while still avoiding interior damage.
Do I Have a Belly?
I’m not talking about a giggly gut here, a belly is a common plumbing issue that requires room to repair it properly.
Sometimes the issue isn’t a crack or a break—it’s a low spot, or a “belly,” in the drain line. These sagging areas of pipe collect water and waste, which then cause backups and blockages over time.
A tunneling approach can give plumbers adequate access to remove and correctly slope the affected pipe and repair the belly issue.
Handling Under-Slab Leaks Well Is Important
Under-slab tunneling is a big job and repairing under-slab drain lines is essential to do right the first time so you don’t create more issues (like foundation issues) or have to do it again. Tunneling is also a smart and clean solution to a major problem.
If you’re dealing with a drain line issue under your slab and you want to fix it without wrecking the inside of your house, a tunneling approach is definitely worth considering.
At Anchor Foundation Repair, we’ve helped many homeowners through this exact situation. If you’re not sure whether tunneling is necessary—or just want to talk through your options—we’re here to help.
Contact us to get expert tunneling advice (and a free quote) and move one step closer to getting everything flowing freely through your under-slab drain lines again.