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How to install plumbing in a concrete slab

Updated February 21, 2017

Plumbing is never installed horizontally through a concrete slab-on-grade--a slab that is on the ground. All plumbing lines are run beneath the slab at varying depths and pitches in the soil. The lines then "stub-out" vertically through the slab to allow for later connections to be made. The process to install your plumbing in a concrete slab is physically demanding and mechanically exact. You must install the plumbing to the exact specifications detailed in your construction drawings.

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  1. Mark where you will need to dig to place your plumbing by using a tape measure and spray paint. Pay close attention to the measurements given in your construction drawings on where to locate each line beneath the concrete slab. Mark the actual pipe lines with a spray paint line but also mark where the pipes are to stub out of the slab with a "X" placed in a circle. Put this mark a few feet off the line that marks where you will dig so you will not lose the mark where you excavate your pipe trench.

  2. Excavate your pipe trenches. Depending on the length of the slab and the depth of the placement required, you may want to use a mechanical excavator rather than a hand shovel. Make sure that you follow all applicable OSHA rules for safely excavating a trench.

  3. Install your pipe and all connections in your pipe trenches. Make sure that the plumbing pipe is supported by pipe stands of the type specified in your construction drawings. Provide a vertical connection at the stub-out locations for each pipe that must pass through the slab. Make these stub-out pipes long enough to extend a minimum of 6 inches above the top of the concrete slab.

  4. Cover the openings of all stub outs with duct tape to prevent debris from entering the pipeline. Concrete or soil debris that enters the line can form a clog in the pipe that you will not be aware of until the pipe is connected. By then, you will have to break through the concrete to access the pipe to remove it.

  5. Use a hand shovel or excavator to back fill (cover with dirt) over the plumbing lines. Completely fill the trench so that the back fill is level with the soil of the bottom of the slab area.

  6. Tip

    Spray paint the stub out pipes of your plumbing lines so that they can be easily seen by anyone working in the slab area. Pipes that cannot be seen are often broken before the slab area is poured by the machines and workers finishing the soil preparation for the concrete.


    Wear appropriate safety equipment when installing any kind of plumbing. This includes safety shoes and back support systems. Even if you are working with PVC pipes their weight can strain your back of crush your feet if you are not adequately protected.

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Things You'll Need

  • Tape measure
  • Spray paint
  • Shovel
  • Excavator (if needed)
  • Pipe supports (as specified)
  • Plumbing pipe and connectors (as specified)
  • Duct tape

About the Author

Cassandra Tribe has worked in the construction field for over 17 years and has experience in a variety of mechanical, scientific, automotive and mathematical forms. She has been writing and editing for over 10 years. Her areas of interest include culture and society, automotive, computers, business, the Internet, science and structural engineering and implementation.

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