How Deep Are Plumbing Pipes Under A Slab House?

Last Updated On September 13, 2022
How Deep Are Plumbing Pipes Under A Slab House

If you’re wondering how deep your plumbing pipes go in the floor, you’re not alone. A lot of people have this question, especially those who are buying or selling a home with a slab foundation. 

In this article, we’ll answer that question and also provide some tips on how to deal with slab leaks if they occur.

In this PlumbingNav guide, we will also cover

  • What you need to know about plumbing pipes underneath a slab house
  • Shallow underground pipes: problems and solutions
  • Pipes and your concrete slab foundation

What's In This Guide?

      What You Need To Know About Plumbing Pipes Underneath A Slab House

      You have three underground pipes coming into your home: water line, sewer line, and a gas line if you have natural gas. (Some homes are 100% electricity.) 

      Regulations regarding how deep each pipe varies based on the type of pipe, pipe material, and location.  Standard requirements may not apply to manufactured homes. 

      Colder climates generally require deeper burial than warmer climates. 

      For example, water lines and sewer lines in Illinois should be buried between 48” – 60” underground. 

      Pipes don’t deep to be buried as deep in San Diego. See the following example of how deep lines must be outside of buildings in San Diego:

      • Water line (metal) – 12” recommended – no burial required
      • Water line (plastic) – 12” minimum
      • Sewer line (metal) – 12” recommended – no burial required
      • Sewer line (plastic) – 12” below water pipe
      • Gas line (metal) – 6” above ground for black iron/galvanized iron or 12” below ground for factory coated or machine wrapped piping
      • Gas line (plastic) – 18” minimum

      Check with your local municipality for specific information regarding how deep your pipes should be in your area.

      Shallow Underground Pipes: Plumbing Problems and Solutions

      Pipes require burial to prevent damage, corrosion and freezing. You can avoid a plumbing problem by ensuring your pipes are properly buried.

      Shallow pipes are more susceptible to tree root damage and other physical damage caused by lawn work or pests. You can use tree root killer to stop roots from infiltrating your pipes.

      Corrosion occurs naturally to all-metal material over time, especially when the metal comes into contact with water regularly, as with your plumbing lines. Hot water speeds up the corrosion process, too, making lines connected to your water heater more susceptible.

      The corrosion process of underground pipes occurs differently thanks to the different conditions underground, such as:

      • Moisture content 
      • Oxygen content 
      • Chemical properties 
      • Pipe coating/ pipe lining
      • Stray currents from nearby buried structures

      If your pipe freezes, the water inside the pipe expands, potentially leading to a burst pipe (and expensive pipe repair costs). 

      Plastic tubing, such as PVC pipe or PEX pipe, requires deeper placement than metal tubing. Learn more about whether PEX pipes freeze.

      Despite burying the majority of the pipe, you may still have an exposed water bib. You will want to install a freeze-proof faucet outside or cover the faucet with an outdoor faucet cover.

      Pipes and Your Concrete Slab Foundation

      A slab foundation is one of three main foundation types to support your home alone with a crawl space foundation and a basement foundation.

      There are multiple advantages to concrete slab foundations for both residential and commercial plumbing. They are inexpensive and preferable in areas with expansive soil. They can also work well to prevent water damage (assuming the concrete doesn’t crack). 

      Did You Know? A slab foundation is the cheapest type of foundation available.

      Did You Know Adid you know slab foundation is the cheapest type of foundation available.

      However, a concrete slab makes it difficult for homeowners and plumbers to access the underground pipes. It can also make it difficult to “tie into” with additions or when running plumbing to a detached garage. They also don’t work well in colder climates, benefitting from a shallow frost line. Furthermore, you can’t finish the foundation to turn it into a living space. 

      A drain pipe underneath a slab foundation works using a gravity-flow system. Essentially, the plumbing pipe is buried underneath the slab in gravel or sand, and it gradually descends until it reaches the public sewer pipe or the septic tank.

      Generally, the pipe starts 6” underneath the slab.

      What to Do If You Have a Slab Leak

      While concrete holds up well against water damage, especially compared to wood and other building materials, water damage will play a substantial role over time. 

      A slab leak can occur for a number of reasons, including drain clogs, changing conditions underground from settling soil, corrosion, and frozen pipes.

      Signs you have a slab leak include:

      • Cracks in walls
      • Damp ground floor
      • Warm spots
      • Warped or buckling floor boards
      • Foul odor (mold)
      • Pools of water 
      • Increased water bill
      • Sound of rushing water
      • Reduced water pressure 

      Resolving a slab leak immediately can prevent advanced damage. Perform a visual inspection around your home and get slab leak detection to ensure the location of the leak. You can also perform a hydrostatic plumbing test. Then, you will need to hire a plumber to complete the repairs.

      Stay on top of your slab pipes by getting regular sewer line inspections. Most homeowners hire a professional to perform an inspection, but you can inspect your sewer line yourself with a sewer camera locator

      Even if you perform a plumbing inspection yourself, keep in mind that slab leak repair will require the assistance of a professional plumbing contractor. Thankfully, trenchless repair methods such as CIPP, pipe relining, and pipe bursting now exist to make this more affordable. 

      Read the following PlumbingNav guide on what is a slab leak or watch the video below to learn more.

      Cost of a Slab Leak

      A slab leak won’t necessarily be light on the pocketbook. The average cost to repair a slab leak comes to about $2500, which is more than standard sewer line repair. You may also need to pay for repairs to the foundation or any water damage that occurred to your home.

      You will also end up spending a lot of money on wasted water. 

      See the following estimated cost of a leaking pipe based on the diameter and how long the water leak continues:

      DiameterWater lost (day)Water lost (year)Cost per year ($1.42/ 1000 gallons) Cost per year ($1.91/ 1000 gallons)
      1/16”822300,030$426$573
      ⅛”28501,040,250$1477$1,987
      ¼” 11,4004,161,000$5909$7,948
      ½” 45,60016,644,000$23,634$31,790

      Preventing a Slab Leak

      Slab leaks generally occur when the pipes freeze, the pipes get old, the pipe get damaged on the supply side. For drains, a drain clog can crack when clogged while under excessive pressure levels. 

      Inspect your underground pipes regularly and perform regular drain cleaning using an enzymatic drain cleaner regularly before a clog develops and using an electric drain auger after you notice a drain clog.

      FAQs: How Deep Are Plumbing Pipes Under a Slab House

      How are water pipes run under a slab?

      Most houses these days are built on a concrete slab, which is a single layer of concrete that covers the ground. This can make it a bit trickier to run underground pipes, like the sewer line and water line. The first step is to dig a trench for the pipes. 

      The trench needs to be deep enough so that the pipes will be underground, but not so deep that they’ll be too difficult to reach if there’s ever a problem.

      Next, the underground pipes are laid in the trench and connected to the house. Finally, the trench is backfilled and the slab is poured. 

      How long does under slab plumbing last?

      The underground pipes that make up your home’s plumbing system are designed to last for many years.

      Metal pipes, such as those made of copper or galvanized steel, can last for up to 100 years. Plastic pipes, on the other hand, generally last from 50 – 75 years. 

      The type of pipe used will depend on a number of factors, including the climate and the soil conditions. In general, you can expect your underground plumbing to last for many years with proper maintenance.

      How do I find under slab plumbing?

      There are a few different ways to locate underground plumbing. 

      One option is to use an endoscope, which is a thin, flexible tube with a camera on the end. This can be inserted into small openings in walls or floors in order to see inside underground pipes. 

      Another option is to use special radar equipment that can detect the presence of underground pipes. 

      Once the general location of the pipes has been determined, it will be easier to narrow down the exact location of the leak.

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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