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What Is a Slab Leak?

Margaret Wack
Written by Margaret Wack
Updated October 21, 2021
grey and red house on concrete porch
Iriana Shiyan -

Learn to spot the signs of a slab leak to keep your home’s foundation strong

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You may not give what your house sits on top of much thought—until there’s a problem. Most homes’ foundations are built on top of a solid concrete slab. A slab leak refers to a leak that occurs underneath this slab. If left untreated, they can damage the foundation, floors, and walls of your home. But by keeping your eyes peeled for telltale signs of a slab leak, like cracks in your walls and unusual sounds, you can help protect your home’s foundation. When it comes to spotting a slab leak, here's what you need to know.

Signs of Slab Leaks

If you have a leak in your roof or your basement, chances are you’ll notice it as soon as you step into the room. But if your home has a slab leak, it can be a little more difficult to detect. Here are some signs to look out for.

Warm Floor

One common sign of a slab leak is a warm spot or spots in your floor. This could indicate that there’s a leak in your hot water pipe that’s causing a slab leak.

Running Water Sound

If you hear running water when no appliances in your house are using water, it could be a sign that a pipe has burst and is causing a slab leak. You may also hear a hissing sound from a smaller leak.

Cracks in Your Foundation or Walls

Over time, even a small slab leak can cause some serious damage to your home’s foundation, walls, and ceiling. While slab leaks aren’t the only cause of cracks in your walls or foundation, if you see any cracks in these locations, it could be a sign of a slab leak.

High Water Bill

If your water bill is climbing even though your usage has remained steady, it could mean that there’s a burst pipe beneath your home. You should get in touch with a plumber near you to inspect your home.

Puddles or Water Damage

Puddles or visible water damage like warped or moldy floors are another possible sign of a slab leak. These puddles often occur in areas near major plumbing components, like bathrooms and kitchens.

What Causes Slab Leaks?

There are a few common causes of slab leaks, including leaky or broken pipes and soil shift.

Pressure on Pipes

Pipes buried underground are often subject to significant pressure. This pressure can increase if you experience an earthquake, or if the ground underneath your foundation shifts. If a pipe is under too much pressure, it may burst and cause a slab leak.

Plumbing Materials

Some plumbing materials are more susceptible to leaks. In particular, galvanized steel or cast iron pipes are vulnerable to corrosion. Other pipe materials, such as plastic, also suffer from abrasion as a result of small vibrations.

Soil Shift

If the soil shifts underneath your home, it could cause a slab leak and damage your foundation. Soil that absorbs water and expands can damage pipes and contribute to leaks underneath your home.

How to Fix Slab Leaks

It’s important to fix slab leaks right away. Slab leak repair isn’t a good fit for a DIY project, since it requires skills and experience the average homeowner lacks. If you think there might be a leak beneath your home you should work with an experienced contractor who will assess the situation and recommend next steps. Depending on the size and location of the slab leak, they may recommend that you reroute the leaky pipe or even repipe your whole house.

FAQs About Slab Leaks

How much does it cost to repair foundation damage caused by a slab leak?

If your home’s foundation is damaged as a result of a slab leak, you’ll need to repair it in order to preserve the structural integrity of your home. Foundation slab leak repair costs around $2,300.

How much does a new concrete slab cost?

The cost of a new concrete slab is between $3,600 and $7,200. Costs vary depending on the size, thickness, and placement of the slab.

What else causes foundation damage?

Slab leaks aren’t the only way your foundation can be damaged. Other causes of foundation damage include expansive soil, frost heave, and varying foundation depths.

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