average cost of tunneling

What Is the Average Cost for an Under-Slab Tunneling Job?

What is the price of digging a tunnel? Not just any ol’ tunnel, we’re talking about a tunnel that goes under a home to allow for the repair of under-slab plumbing. You want to know exactly how much under-slab tunneling will cost.

Anchor Foundation Repair

At Anchor Foundation Repair, we tunnel under homes on a weekly basis and use tunneling as part of foundation repair projects as well as independent from foundation repairs. We offer under-slab tunneling as one of our primary services and can for sure tell you how much it usually costs.

Although we do tunneling ourselves, we will present this information in a general way so that it covers average costs between companies. Although our costs will certainly fall within the ranges we quote, this isn’t just our specific pricing.

This article will discuss how tunneling costs are determined, and what contributes to the price. We will also review what a typical tunneling job might involve and how much it would cost for small, average, and larger tunneling projects.

Refresher: What Is Under-Slab Tunneling?

the alternative to under-slab tunneling
Breaking through your slab instead of tunneling

Just a quick explanation about what under-slab tunneling is and its benefits to homeowners. Under-slab tunneling is a non-intrusive way for your under-slab plumbing leaks to be accessed and repaired. 

All the mess, chaos, and repair people stay outside your home because the repairs are done outside and underneath your house through the under-slab tunnel instead. The benefit of living normally without major life disruption while having a vital repair done to your home is very appealing to some.

The alternative to tunneling is breaking through your slab from the top by jackhammering. This can damage flooring, compromise the strength of your slab foundation, and is loud and messy. You might have to avoid areas of your home and normal living routines can be impacted.

The alternative of jackhammering can sometimes be less costly and faster than tunneling, but it might not be either. BUT some homeowners find that a higher cost and work time of tunneling is worth the benefit of being able to stay in the home without major disruptions.

How Much Does Under-Slab Tunneling Cost?

under-slab tunneling to repair plumbing

Like many repairs needed around the home, the cost will vary depending on your individual home and situation. Most commonly, under-slab tunneling is priced by the foot so the exact length of the tunnel is important. The price per foot is the best place to start when estimating the cost of tunneling.

Price Per Foot 

Expect the average price of tunneling to fall somewhere in the $200-$500 per foot range. This price point will vary from company to company and location to location. Tunneling costs do fluctuate and also depend on the cost of materials in a particular area. 

Some plumbing companies might even charge as much as $600 per foot for tunneling.

Typical Example Project Cost

A typical example might be a traditional hall bathroom with leaking drain lines. A diagram is shown here that illustrates where the plumbing drain lines are located (by the blue lines) and where the tunnel would be created (by the red rectangle) to access all three of the drain lines in this example bathroom.

tunneling path diagram

This project needs about 8 to 10 feet of tunneling. So using the price per foot range of tunneling above, this project could cost between $1,600 to $5,000 for the tunnel in this job. That’s a pretty big range so let’s try to narrow it down a bit.

The cost of the tunneling and backfilling in this example would be somewhere between $3,000-$5,000 in this area. This price is based on the local area of Bryan/College Station and typical tunneling needs for this hall bath example. 

The cost of a complete project will also vary based on the amount of repair needed to be done to the home’s plumbing. The cost for the plumbing repairs would be determined by the plumber and be in addition to the tunneling cost.

What Contributes to the Cost of Under-Slab Tunneling?

So we have already talked about how tunneling prices are usually calculated per foot of tunnel. But a few more things might contribute to tunneling costs and drive the price up or down accordingly.

More Leaks = Higher Costs

If you have more than one leak under your slab, the cost will be higher. The tunneling crew might have to dig two separate tunnels to reach repair locations on opposite ends of the home. You might need a tunnel that branches off in a few directions to reach all the leaking areas. But still, the total number of feet will contribute to the overall cost.

under-slab plumbing repaired by tunnel access

Sometimes a plumber will fix one leak and everyone thinks the job is done. But after doing a hydrostatic plumbing test, another leak could be identified later. All the leaks need to be repaired so costs will increase if additional leaks are discovered during the project.

starting a tunnel

Starting Point Adjustments

The tunneling crew might have to adjust the starting point of their tunnel because of an obstacle. Typical obstacles might include a sidewalk, tree, or A/C unit. If the tunnel needs to be started farther out away from the home to avoid these obstacles, it will add more feet to the tunnel and therefore more cost.

Concrete Chipping

Even when tunneling is used, sometimes concrete still has to get chipped to fully access a leak or tie in properly to undamaged lines. If a plumbing line runs through a support beam there is extra work that must be done to break out the line. Breaks most often occur at elbows and couplings and they are sometimes encased in concrete. 

Extra charges can be incurred when the need for chipping concrete arises. Plumbers can do this too, but they might not want to and charge more for it.

Backfilling and Mud-Pumping Services

tunneling, backfilling, and mud-pumping

It’s not just about digging the tunnel, it’s about filling the tunnel back in as well. You want to make sure that the tunnel is filled properly and that opportunities for foundation settlement and slab compromise are reduced as much as possible too.

About Backfilling

Backfilling a tunnel is usually done using some of the previously excavated dirt as well as bringing in new topsoil too. Depending on how much new dirt is needed and its cost, this can contribute somewhat to the overall cost. Topsoil pricing doesn’t fluctuate like crazy or anything, but it is a material cost that contributes to the total price.

About Mud-Pumping

After backfilling as much as possible with dirt, a technique called mud-pumping is used to completely fill the tiniest of spaces under your home created by under-slab tunnels. 

Mud-pumping uses a mixture of topsoil, water, and Portland Cement (called slurry) to create a flowing mud-like mixture. This slurry is pumped underground and hardens to a sandstone-like consistency that supports the slab and minimizes any possible chance for movement in your foundation after the repairs have been completed.

The mud-pumping process will add to the cost of tunneling if a company uses this finishing method. Sometimes the cost is incorporated into the price per foot of tunnel, but it can also be listed as a separate line item.

mud-pumping the tunnel after use

A company can certainly choose not to use mud-pumping to fill the voids under your home after backfilling. But check out the reasons why mud-pumping is used and beneficial for the health of your home’s foundation with this article, “What is Mud-Pumping?” 

Even though the article above is about voids under your home due to foundation repair, the same principles apply to voids created by tunnels.

Pricing for Small, Medium, and Larger Under-Slab Tunneling Jobs?

So you’ve got some basic per foot pricing for tunneling and you even have some sample costs for a typical sort of hall bath project. But maybe you want more pricing estimates like for a small job vs. a medium job vs. a major project. We’ve got those tunneling costs too!

For a small project that needs 4 feet of tunnel or less, the typical costs would be around $2,200 or less to reach a plumbing issue near the edge of your home. This would be for something like a kitchen sink, tub, or toilet near an outside wall.

An average-sized project with 8 to 15 feet of tunneling needed, would be between $4,500 to $7,000 to access a plumbing leak closer to the center of your home. This would be for a project that covers multiple fixtures in one room. Like the sink, toilet, and shower drain in a hall bath.

For an extensive tunneling job that would need 60 or more feet of tunnel and cover your entire under-slab drain system, the tunneling costs could be $24,000 or more. This kind of project might be needed due to faulty, old, or rusted-out cast iron drain lines. 

This kind of large project depends a lot on the layout of the home and the number of starting locations needed to remove and replace whole drain lines.

Remember that these estimated costs are only for the tunneling and do not include the bill from the plumber for their part of the repair services. *Pricing ranges are for our area of Central Texas and are estimates for educational purposes only.

Ready To Get A Bid For Under-Slab Tunneling?

digging an under-slab tunnel in BCS

Although Anchor does not fix the actual plumbing issues (we let the plumbing experts do their part), we can recommend some great plumbers in the area. We love working with plumbers of integrity who understand our process and the importance of doing the job in the least intrusive and most stable way for you and your home.

At Anchor Foundation Repair, we can expertly handle your under-slab tunneling needs with care. We do tunneling as part of foundation repair jobs, but also on its own if all you need is a way for plumbers to get under your home to complete a repair. We charge $400 to $500 per foot for under-slab tunneling (depending on the total length) in case you are wondering.

So if you think you would prefer under-slab tunneling as the best way to access those plumbing repairs, reach out to us for a bid and get an accurate quote on the cost of your under-slab tunneling project.