Build A French Drain to Improve Barn Drainage

Before and after photos showing how installation of a French drain improves drainage.
Before and after photos showing how installation of a French drain improves drainage. - Comcast Washington State


Wet areas around the barn are troublesome to work in and can become breeding grounds for insects that carry diseases. You may think that standing or pooling water near your barn is simply a nuisance, but it may be a bigger issue and can pose a threat to your horse’s health and even erode the structure of your barn.

Standing water in the barn area

Standing water - a health and safety hazard

Installing a simple french drain can help with drainage in  your horse barnyard.

Water naturally collects in areas with poor drainage. Permeable soils, like sand, have void spaces between the soil particles, allowing water to quickly filter into the ground. Heavier, clay soils are denser, with less void space for water to percolate back into the earth. The topography (slope) of the land can also contribute to creating soggy areas.

If you are planning construction for a new barn, carefully evaluate where on the property the barn will be built. Poor site selection can compound drainage problems. Properly preparing land for barns can be a costly addition to the construction process. Additional dirt may be needed for a foundation, and labor costs associated with grading and leveling the soil can add up. However, if these steps are compromised, the barn may never be fully functional.

On the other hand, if you are trying to alleviate excess water from an existing property, the installation of a French Drain subsurface system may be the solution for you. Keep in mind, correcting frequent flooding or severe drainage issues will require the help of an individual experienced in drainage design, or even an engineer.

French Drain systems have been in use for centuries. In its most basic form, a French Drain is a trench filled with gravel. Sand is placed over the top of the gravel and sod or grass seed can be planted to make the area less noticeable.

Some French Drains include a pipe inside the trench. The pipe will be perforated to allow water flowing through the pipe to discharge at different points along its length. The pipe can be a piece of rigid, smooth, white PVC pipe with pre-drilled holes or a piece of flexible, black, corrugated pipe with slits.

Preparing For A French Drain

A walk-behind trencher does the hard work

A walk-behind trencher does the hard work

Rent a walk-behind trencher such as the Ditch Witch can be used to reduce labor. Make sure your trencher has the proper width capabilities for your french drain.
© Ditch WitchNew window.

Before digging any trenches, walk around your barn and look for areas that have standing water or spots that have been churned up by hooves. Both are signs that excess water is beneath the surface.

Study the property and look for any natural slopes. Look for where the water is coming from. Examine the area around the barn and notice if water is draining away from and not into the barn.

The amount of standing water on-site will determine the design of the system. Also the type of soil is an important factor to consider. Finer clay soils do not drain as well as loam or sandy soils so depending on your soil type, you may need to increase the length and width of your french drain trench.


“Call Before You Dig” is a new, federally-mandated national call line that was created to help protect property owners from unintentionally hitting underground utility lines while working on digging projects. Simply dial 811 and provide your location, and the system will notify your local utility companies that work is scheduled for your property so the utility company can flag the lines. The website includes additional information.

It is also a good idea to investigate the local code requirements prior to installing any drainage system on the property.

The most important aspect of installing any drain system is the slope. Gravity guides water from one point to the next. At a minimum, the trench should have a 1/8” per foot, or 1%, slope when using smooth pipe, and 2% when using corrugated pipe. In most systems, a random design, meaning a trench is dug to discharge water from one point to the next, will suffice.

For properties with significant water problems, a herringbone or grid pattern is more effective. Working with an engineer is strongly encouraged for the design and installation of complex systems.

Planning for the drainage system can be the most time-consuming portion of the entire project. Carefully preparing for the installation will ensure the system alleviates the excess water rather than compounding it.

With all of the preparation completed, it is time to get started.

Start Digging

Coarse rock as a pipe base

Coarse rock as a pipe base

After trenching, place coarse rock as a base to separate the pipe from the soil.

Placed pipes with filler rock

Placed pipes with filler rock

This french drain has two pipes for greater drainage capacity. The perforated drain pipes help distribute the water throughout the trench.

Cleanout with a pipe going to the wash rack

Cleanout with a pipe going to the wash rack

It is a good idea to have a cleanout for flushing the pipe (have one at both ends). Also, this french drain is connecting to a wash rack - a great idea.

The first step to installing a French Drain is to dig the trench. The size of the trench varies, but typically a trench 5” to 6” wide and 8” to 12” deep will suffice for most situations.

For a French Drain without the pipe, fill the trench with gravel between 0.5” to 1” in size. Leave approximately 3” to 4” from the top of the trench for sand. Once the trench is lined with gravel, fill the remainder of the trench with the sand. It is important to use coarse sand to allow the drain to filter excess water properly.

To install a French Drain with a pipe, the process is very similar. Dig a trench and line the bottom with 1" to 2" of gravel. Place the pipe on top of the gravel.

The pipe can be purchased “with a sock” or “without a sock.” The sock is a fabric that covers the pipe and keeps debris and soil particles from clogging the pipe’s pores. If you purchase pipe “without a sock” you will need to purchase a non-woven fabric to wrap around the pipe before filling in the trench.

The size of the pipe used will vary based on the amount of water being moved. The most common pipe sizes are 4” and 6” pipe, which will easily fit into a trench that is between 6” and 8” wide.

Where possible, run the end of the drain pipe to the surface and cap it off so that if the pipe ever becomes clogged you have an access point to work on the drain without having to dig up the entire pipe.

A No-Fill Alternative

One drawback to using a traditional French Drain system is the amount of labor associated with larger systems. First, a trench must be dug and dirt removed. Then, gravel and sand must be brought in to fill the trench and the leftover dirt must be carted away.

Manufacturers have started designing systems like the EZ-Drain made by NDS. These pre-engineered subsurface drainage systems eliminate the need for multiple materials and extra labor. All of the components needed are pre-packaged into one piece and installation is as easy as a three step process.

  1. Dig the trench.
  2. Place the pre-engineered French Drain system in the trench.
  3. Backfill the trench.

The EZ-Drain must be covered with a minimum of 6” of soil.

French Drain systems are the most basic type of subsurface drainage system available. The concept of French Drains has been used for centuries to help property owners alleviate excess water. Compared to other types of systems on the market, the investment cost can be measured in sweat equity, rather than in supplies and materials.

Dig deeperTM

For more information on the EZ-Drain system, check out the NDS website. If you liked this article and would like to learn more about horse barn safety, visit our healthy barn health center.

About the Author

Katie Navarra

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Katie has been a freelance writer since 2001 and has more than 250 bylines to her credit.  In addition to writing for equine publications, she also writes for landscape, general agriculture and business publications.