Concrete Slab Foundation for New Home
© 1jaimages / Fotolia

As a responsible homeowner, you do your best to keep an eye out for any maintenance trouble brewing around your house. While a lot of maintenance issues are easy to spot with quick inspections, others develop out of sight. A slab leak is one of these. This type of leak can eventually cause major damage to your home, but you can prevent this by knowing the signs and understanding how to solve the problem.

What is a Slab Leak?

Under Slab Plumbing
Plumbing Pipes Before Concrete Slab is Poured
Photo Credit: Roger Mommaerts

Most modern homes have concrete slab foundations in which a layer of concrete is poured or placed onto a soil or gravel surface. The house is then built on this slab. Any damage to the slab undermines the structural integrity of the entire house.

A “slab leak” is what happens when your plumbing system leaks under the concrete slab foundation. This can lead to a number of issues that will only get worse if the leak isn’t stopped. There are several possible causes of slab leaks.

Excess pressure – Underground pipes are often placed under heavy pressure, which can eventually cause them to crack. This is a common problem in areas with clay soils, which expand when wet and shrink when dry, causing the ground under the foundation to shift and put pressure on the slab and pipes. An earthquake can also cause this situation.

Corrosion – Pipes underground are in direct contact with the soil and the metals it contains. This can lead to galvanic corrosion caused by contact between two different metals. This kind of corrosion can eat a hole in your pipe and cause a leak.

Abrasion – Water flowing through the pipes causes them to vibrate. If the pipe is next to a hard surface such as concrete, rebar, another pipe or even gravel, the metal will wear away at the point where it rubs against that hard surface. Eventually, a hole forms and the pipe leaks.

Slab Leak Symptoms You Should Never Ignore

Home Water Meter
© bartsadowski / Fotolia

The symptoms of a slab leak aren’t always obvious and some are easy to mistake for other issues. If you notice any of the symptoms, however, it’s a good idea to investigate. A slab leak can do major damage in a relatively short amount of time.

The sound of running water – If you hear water running under your floor when none of your taps or water-using appliances are on, there’s a good chance you have a leak.

A hot floor – A floor or part of a floor that’s unusually warm suggests a leak in the hot water lines. Walking barefoot on the floor will make hot spots easier to detect.

Puddles – Puddles along the side of your house that have no obvious origin, such as a leaky hose bib, could be coming from cracks in your foundation caused by a slab leak. Indoors, you might find puddles on the floor emerging from underneath a cabinet, from between tiles or from the bottom of a wall. This is most likely to happen in the kitchen or bathroom near a fixture or pipe.

Mold – Moisture encourages mold and mildew growth. If you find mold under your carpets, it’s possible the moisture feeding it is coming from a slab leak.

Abnormally high water use – The most obvious sign is that the dial on your water meter is constantly spinning, indicating you’re using water even when all your taps are closed and your water-using appliances are off. A leak in a hot water line will have your water heater constantly running, too.

Finally, you might notice your water bill is much higher than usual. These issues usually indicate a leak somewhere in the plumbing system, you’ll need a professional inspection to determine if you have a slab leak.

Cracks – A crack in your slab foundation or in your walls or flooring could be caused by water damage due to a slab leak.

Professional Slab Leak Detection

Even if you notice signs of a slab leak, you’ll still need to confirm whether or not you really have a damaged underground pipe. There’s no need to break the foundation open to do this, though. Don’t let a plumber open your foundation before they’ve confirmed the existence of a leak by other means.

Modern technology allows for accurate, non-destructive slab leak detection. Most companies equipped to detect and repair slab leaks use sonic equipment such as ground mics and acoustic systems. These pick up on the noise made when a leaky section of pipe vibrates due to water leaving it at a high speed. They may also use sonic location systems to pinpoint non-metal pipes and video pipe inspection equipment.

Options for Repairing Slab Leaks

There are three basic approaches to dealing with a slab leak. The option that’s best for you depends on the extent of the leak as well as the condition of the pipe and the rest of your plumbing system.

Repair the damaged section – If the leak is minor and the pipe is in otherwise good condition, this is generally the most practical option. The leaking section of pipe and related fittings can simply be replaced. Epoxy pipe lining is another possible option. This involves lining the interior of the pipe with epoxy to seal the leak and doesn’t require breaking the foundation.

Reroute the pipe – If the leaking pipe is old or in poor condition, repairing a leak in one spot could cause a leak to spring somewhere else on that pipe. In this case, the best option may be to shut off the pipe at the closest manifold and re-route it. The pipe will typically be rerouted above ground.

Repipe the house – In an old house where the whole pipe system is deteriorating, a slab leak is often a sign that you’ll soon be seeing leaks in other parts of the system. By repiping the house, you’ll head off future leaks and the damage, repair expenses, and stress they bring.

Estimating and Covering the Costs

The cost of slab leak repair starts with the cost of detection, which usually ranges from $125 to $375. Companies that specialize in slab leak detection and repair tend to charge more based on their expertise and sophisticated equipment.

Opening the foundation and repairing the leaking pipe could cost you as little as $500, but it can run as high as $4000 if the leak is extensive, the pipe is difficult to access, and rates for plumbing services are high in your area. A leak in a sewer drain will typically cost you around 25 percent more than one in an ordinary pipe.

For a deteriorating pipe that’s best rerouted, the rerouting job can cost between $200 to $500 for short pipes. For most pipes, however, the prices will be closer to $1500 or even higher in complex situations.

Homeowner’s Insurance

Homeowner’s insurance often covers part or all of the costs related to a slab leak. If a simple repair is all you need, your insurance will most likely cover the cost of demolition (breaking into the foundation and closing it again) and pipe replacement, but it may not cover the labor costs involved. A “tear-out provision” in your policy means the cost of demolition should be covered.

Rerouting and repiping are generally not covered, but because they reduce the risk of leaks and water damage inside your home, you can petition your insurance provider to adjust your rates after the job is done.

Policies vary widely and some don’t cover water-related damage at all while others cover only physical damage caused by a leak that occurred suddenly. This refers to damage such as a ruined floor or wall, but not damage caused by plumbing repair work. If only sudden leaks are covered and you noticed signs of a leak, such as a warm floor, before the leak caused damage, you might not be eligible for a payout.

If you notice signs of a slab leak, contact a plumber as soon as possible. Look for a plumbing company with experience in slab leak detection and repair. The earlier you address the problem, the less water damage you’ll have to deal with under your foundation and inside your home.

Editorial Contributors
Henry Parker

Henry Parker

Henry Parker is a home improvement enthusiast who loves to share his passion and expertise with others. He writes on a variety of topics, such as painting, flooring, windows, and lawn care, to help homeowners make informed decisions and achieve their desired results. Henry strives to write high quality guides and reviews that are easy to understand and practical to follow. Whether you are looking for the best electric riding lawn mower, the easiest way to remove paint from flooring, or the signs of a bad tile job, Henry has you covered with his insightful and honest articles. Henry lives in Florida with his wife and two kids, and enjoys spending his free time on DIY projects around the house. You can find some of his work on Today’s Homeowner, where he is a regular contributor.

Learn More