Planning a French Drain

A French drain.
  • 8-12 hours
  • Beginner
  • 100-400

People have been faced with the problem of getting rid of excess water on their property for hundreds of years and one method that has stood the test of time is a French drain. Essentially a small, covered stone-filled ditch, French drains take advantage of the power of gravity to create a route for the excess moisture to be channeled from where it isn’t wanted to an area where it won’t be a problem.

Besides helping turn wet, soggy garden areas into productive ones, French drains can also be used to channel runoff water away from a home’s foundation and help prevent basement flooding.

What’s French About a French drain?

In reality, there’s nothing really French about them. Although some people say the name comes from the fact the sewers of Paris in the early 1800s were simply open ditches, most attribute the name to a Massachusetts farmer named Henry French. Reportedly, he came up with the idea of using small stone-filled ditches to drain water off his farmland back in the late 1800s.

How Does a French Drain Actually Work?

The idea is simplicity itself. Dig a trench running from the wet area towards a dry or unused area, line it with stone to prevent soil erosion, install PVC piping to channel the water and cover it up. Depending on how much water needs to be moved the drain itself can be as narrow as 6” or as wide as 2’.

The only tricky part is for the water to flow, the drain needs to have a downward slope with a 1 percent grade. (In other words, the drain must go down 1’ for every 100’ in length).

Planning a French Drain

While the concept of a French drain is simple, installing one requires some upfront planning and preparation before beginning.

Since a French drain needs to start at a high point in your yard and run to a low point you need to determine the best route it. Preferably, look for an area running along the edge of your property where digging would be relatively easy. You need to consider if your planned route will impact how you actually use your yard (does it run through a kid’s play area or near a family fire pit?) or if it will impact any planned home improvements.

After you have determined your drain’s routing remember you will need to ensure your finished drain has the proper 1 percent downslope. You can either do this by having a survey done or do it yourself using two wooden stakes, a line level and a piece of twine. It can be done in four easy steps:

First, drive one stake in at the top end of your drain and fasten the string to it.

Next, go to the far end and loosely tie the string there.

Attach your string level and level the string, adjust the loosely tied end and fasten it.

Now, since your drain needs to fall 1 foot for every 100 feet of its length, you can easily calculate how much it needs to go down along its length. (For example, a 50-foot long drain need to go down 6” in total over its length). Simply move the string on the lower stake down the necessary amount and it will be a guide for the proper grade.

Some Other Considerations

Building a French drain isn’t complicated, but it does require a lot of digging and physical effort. You might want to consider renting a small trencher or hiring a backhoe to do the digging for you.

Before you actually start to dig, be sure to call DigSafe (888-Dig-Safe) to arrange for your local utilities and services to mark the location of their facilities on your property.

Make sure the end of your French drain won’t end up dumping all your runoff water onto your neighbor’s property. You don’t want to solve your moisture problem by starting a feud with a neighbor.

With this know-how, you can decide if a French drain will be the best fit for your needs. If it is, click the link below and get the project started!