How To Install A French Drain

When searching for ways to drain your yard or even your house, you will probably happen upon the term French drain. Although the name may indicate that it is a French technique, it is actually named after its inventor. 

The French drain is over 100 years old and hasn’t lost any popularity since its invention. When this happens, it means that the technique works and doesn’t need to be replaced. That’s what happened with the French drain. 

What Is A French Drain?

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In the mid-1800s, a man named Henry French, who was an American agriculturist, invented the French drain. This is what the man is most famous for, along with being the father of Daniel French, who designed the statue at the Lincoln Memorial. 

Although the statue of Lincoln may be more iconic, the French drain changed the way that we irrigate and drain water. The French drain is a concealed drain with many uses and variations. All of which we’ll learn about. 

How Does A French Drain Work? 

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French drains were created as a way to drain yards and gardens. The pipe itself is hidden under the ground and covered with rocks. It is pierced with holes to allow water from the surface to seep down and enter the pipe. 

The water then follows the path through the pipe and works just like any other pipe. It’s important that the rocks allow water to travel underneath without becoming a hazard for those walking above. 

The purpose of the French drain is to safely transport water that might build up and loosen foundations. Or, as a way to transport water overflowing from septic tanks/to septic tanks. Or one of many other purposes. This is why there are so many variations. 

How To Build A French Drain

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Building a French drain can be done easily by following a few essential steps. While a couple of steps can be skipped. It’s always best to follow expert advice and find someone to lend a hand that has experience building drains. 

Buying Materials

Before getting started, you’ll need to make a checklist and start shopping. All can be ordered online or bought at a hardware store. Here is everything you’ll need to build a French drain from scratch. 

  • Shovel
  • Pipe (PVC with holes or drain pipe)
  • Gravel
  • Fabric liner (water-permeable weed fabric)
  • Topsoil (optional)

Digging A Trench

You need to dig your trench to be about 18 inches deep and 12 inches wide. This will encompass the pipe while giving you a little room to work with. Feel free to go a few inches deeper, but try not to go deeper than 24in. 

As for width, 12 inches is the absolute minimum. It’s important not to go narrower than this or else you’ll run into problems later. Building a bigger trench won’t cost you anything more, but a smaller one can in the end. 

Lining The Trench (Optional)

This is an optional step, but most experts recommend it. There’s no reason not to add a fabric liner to the trench before adding the pipe. A landscaping fabric will do and will prevent weeds from growing and disrupting the drain. 

Line the entire trench with it, pulling up over the edges. You can also wrap the drainpipe with fabric if you want, but only one layer of fabric, or else the water won’t drain properly. Make sure the landscaping fabric is of good quality. 

Rock Bed For Pipe

After you line the trench, you can add a thin layer of rocks that will be the foundation for your pipe. With this, you can make up for any flat areas or holes. Make sure the pipe will set securely in the bed. 

The pipe shouldn’t move much when you press down on it. But you also don’t want sharp rocks cutting into a pipe that is thin. So check for sharp rocks before pressing down and testing the pipe’s bed.

French Drain Installation

This is the most important step. Installing the drain itself.  You can either use perforated PVC or a drainage pipe that will bend like an accordion. Lay the pipe along the rock bed, making sure it is stable. 

It’s easier to work with a drainage pipe that is flexible than a PVC pipe. PVC pipe may be solid, but it needs a solid base too. Flexible pipe is, well, more flexible. It’s also cheaper, yet not as strong. So both options have their pros and cons. 

Fill With Rocks

Fill the trench with rocks, covering both sides and the top of the pipe evenly. Don’t leave room for movement or the pipe could shift and crack, or create kinks. Cover it well, all the way up to the top unless you use the next step. 

Add Topsoil (Optional) 

If you decide to cover the rocks and make the French drain “invisible” then leave an inch or two for topsoil. Add the topsoil to meet the rest of the ground and pack it securely. You can then add grass seed.

Keep in mind that if you need to do repairs or make changes, it’s better to have gravel to remove rather than grass and topsoil. This is why most French drains have a gravel cover instead of a topsoil cover. 

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FAQs

Everyone has questions, no matter how experienced they are or aren’t. These are the most frequently asked questions about French drains. 

Where Do I Drain To?

It’s important to have a safe release point. It should be an area below your yard and somewhere with little to no traffic. Digging a pond or something similar is a great way to utilize the release point without causing any further problems. 

Can I Drain Onto A Neighbor’s Property?

Absolutely not. Even if they have a larger property than yours and have agreed to it, it’s not a good idea to drain onto a neighbor’s property. To do so is illegal and unless an agreement is written on paper, it could backfire. 

How Do I Stay On Track?

To make sure that the trench follows the planned path, use flags, spray paint, or a chalk line to mark it before you start digging. This way, even if you have help, the team can stay on track without making any mistakes. 

Can I Drain Uphill?

No. In order for water to move uphill, it needs to be siphoned. This is a completely different type of irrigation system. Pipes should always move downhill. In this case, at least one inch every ten feet.

Do I Need A Permit To Install A French Drain?

It depends on the code in your area. Contact an agricultural expert or official in order to find the city or neighborhood codes. You may be able to dig freely or you may need a permit that gives you the leeway you need. 

Do I Have To Use Gravel For My French Drain?

No. While a gravel drain cover is recommended, you can use soil instead. If you do, you’ll need a corrugated pipe surrounded by polystyrene aggregate. The only thing left to do is wrap it in the fabric and cover it with soil. 

Can I Hire A French Drain Installer?

Yes! This will actually speed up the process and ensure everything is done correctly. You can also call the person who installed it if you have problems. If you can afford it, then this is the recommended route. 

Are There Other Types Of French Drains? 

Yes, there are! French drains come in many different varieties. Here’s a breakdown of what they are and their purpose.

  • Curtain drain – this is a concealed drain that is usually covered in soil with vegetation planted on top. They deal more with surface water instead of groundwater like the standard French drain does.
  • Filter drain – often used interchangeably with a French drain, this type deals primarily with groundwater alone.
  • Interceptor drain – used in city sewage systems or storm sewers. 
  • Dispersal drain – a multi-disperse drain that distributes water from septic systems.
  • Fin drain – a subterranean perforated pipe with a perpendicularly upward placement. They direct water to a traditional drain. 

Finding Someone To Install A French Drain

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It may seem easy at first to find someone to install a French drain for you. Some general contractors can install French drains, but it’s most common for a plumber to install the French drain. Landscaping and waterproofing companies can also install French drains. 

Whoever you hire, make sure they are qualified and know the city codes. The cost of a French drain is usually $2000 and $4000. However, the range can be as large as between $800 and $8000. It depends on your project. 

To figure your own quote, measure how many feet of drain you need. The average cost is $20 to $30 per linear foot or between $1,000 and $1,500 in exterior applications and $45 to $60 per linear foot or $5,000 to $6,000 for internal ones.