Design and Build Your Own French Drain

Edited by Mian Sheilette Ong, Eng, Graeme, Lynn and 4 others

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After a heavy downpour, have you ever felt your house is like a sinking ship? In a way, this is true. Water accumulates at the sides of your house and seeps into the foundation. Although your home's basement was designed to last for decades, if moisture frequently soaks through the foundation over long periods, your foundation may deteriorate sooner than you think. This is especially true if you live in a cold climate, due to the freezing and thawing that occurs. This is a potentially serious issue, and it's common for homeowners to see a lot of chipping near the frost line.

Often French drains are installed to help move water away from the house. A French drain is a simple drainage system that can be designed and built easily. With an efficient French drain, you can look forward to a dry home with a strong foundation, even if strong typhoons come your way. A functional French drain can also help your septic system to function more efficiently. Before you start making your own French drain, it's best to consult the local drain and septic experts in your area first to see if there are any local conditions such as underground wires, that might interfere with your project.

Facts About the French Drain

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The French drain can be a valuable drainage component for any property where water collecting is a problem. It's a simple system that divert water from specific areas in your yard. The first part of the French drain is the higher or elevated end, also called as a drain field. This is where the excess surface or groundwater gets into the drainpipes. The second part of the drain is the lowest or exit point. It's where the water exits the French drain. The required slope for a French drain is at least one percent. This means that every eight feet of the French drain should have an inch of slope. Remember that this system is powered by gravity, so it is imperative that the proper slope is provided.

Having French drains on your property will help relieve water pressure from the walls, waterproof your home, and aid your septic system to control its water load.

How to Design Your French Drain

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Designing your French requires planning. You need to decide on the ideal location. Consider the following when designing your French drain:

  1. 1
    Where Is The Exit
    The location for the drain's exit point should be identified first. Take note that the ideal situation is to remove the water from a saturated part of the property to an area in need of water. Here are some of the best places to serve as exit points:
    1. Choose Nearby. An area that is close to the problem spot will cut down on expenses. Keep the length of the French drain short, as the longer it is, the more money you'll spend.
    2. Street Drainage. Aiming for street drainage will allow the city's storm drain to collect your excess water. You should check with the building department first before you go with this option.
    3. Try For The Sun. If you can, pick an area of your property that is grassy and sunny all day. The sun helps evaporate the water while the grass absorbs it. These elements eliminate excess water much faster.
    4. Use Your Existing Rain Gutter. Connecting your French drain to an established drain line that empties directly into the storm drain, would be cost be a smart choice. Use that existing drain as your exit point.
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  2. 2
    Know The Local Codes
    There are codes in your locality that might require you to install a valve that prevents backflow of water to your lawn if ever a clog occurs. Installing this device usually costs around $500.
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  3. 3
    Nowhere to Drain
    If there is no visible exit point for your French drain, you should consider installing a dry well. A typical dry well has a depth of about 4 feet and a diameter of 1 foot. It is filled with an aggregate (gravel). The excess water the dry well disperses, will be absorbed by the surrounding area.
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  4. 4
    Find The Right Slope
    If your yard is sloped, it's easy to know where the highest spots are, and the lowest. If the slope is slight, and it's unclear to you, these suggestions might help:
    1. Drive a stake into the ground at the site of the problem.
    2. Drive a stake into the ground from a possible drain exit.
    3. Tie a string to both stakes.
    4. Place a line level on the string you tied and pull the string until it is taut.
    5. Gauge the distance from the ground to the string. From here, compute the slope of the drainage. A professional can determine the slope for you. A landscape contractor, civil engineer, or surveyor will use a tripod mounted transit level to determine the slope. This service will set you back $150-250.
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  5. 5
    Plan the French drain's route around utilities and tree roots
    Plan the drain's location to avoid passing through the roots or drip lines. There are free services ( HERE) that will help you perform this task easier.
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How to Build your French Drain

Now that you've designed and planned your French drain, it's time for you to build it. It's a simple construction. Here are things you'll have to do to make your French Drain:

Prepare Your Materials:

  1. 1
    1. 2
      Spray paint for striping
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  2. 3
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  3. 4
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  4. 5
    Topsoil add-on
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  5. 6
    A six-inch drain pipe
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  6. 7
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  7. 8
    Gravel or crushed rocks
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  8. 9
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  9. 10
    Stones for landscaping
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Prepping the French Drain Site

  1. Diverting the water. Scan the area to see where you can re-route excess water diverted by the French drain. Make sure that it won't disturb neighboring areas.
  2. Water runs downward. Make sure you have the most favorable drainage route.
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    Every 50 feet of the French drain should have six inches of slope. There should be no obstructions at all. It should also be a meter from the walls, with a downward slope route.
  3. Mark the drain route.
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    Use the paint to mark the route the drain will take.
  4. Dig your trench.
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    Pattern the digging after the paint marks you made. The width of the trench should be six inches and the depth should be the same as the foundation. The trench should be parallel to your home and horizontal to the slopes.

Making the French Drain

  1. Pour in the aggregate or gravel.
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    Once you have completed digging the trench, pour three inches of gravel along the trench.
  2. Line it with the landscape fabric. Use the geofabric to line the entire length of the trench, over the gravel layer. Leave a 10-inch fabric allowance on either side of the trench.
  3. Install the pipe.
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    The pipe should be placed over the geofabric. Pour gravel over the pipe. There should be five inches between the ground surface and the top of the gravel layer.
  4. Fold the excess fabric.
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    Cover the gravel with the excess fabric. You will create an overlap that will protect the drainpipe.
  5. Cover and fill your trench.
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    With your shovel, fill the trench with topsoil and sand. Use the turf to cover the topsoil and sand. A layer of landscape stones should then be placed around the open end of the drainpipe.
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French drains will definitely help you deal with the excess water problem on your property. Depending on the situation, consulting professionals might be the best choice, but being able to build a French drain system by yourself will not only save you a lot of money, but give you that fine sense of accomplishment.


  • You can increase the angel to your slope by digging one end deeper than the other.
  • Do not use your neighbor's yard as your exit point.
  • Do not let the excess water drain onto the sidewalk or driveway because this will cause slips during winter. And if you do this, you will violate building codes, and you better have your liability insurance up to date, as you would be responsible for any accidents.
  • Do not divert into areas that may erode easily. Places without plants are usually areas prone to erosion.

Questions and Answers

Could I tie into a storm sewer below grade?

My lot is very flat, I have a 3' hole (crawl space). The storm drain with surface grate is in the back of the property.

In many municipalities, it is illegal to tamper with or connect to a storm sewer. You also would have to dig quite a bit to access the storm drain. If you don't have permission to connect your drain to the sewer, the another option is to create a downgrade pond on your property for any overflow, and connect the French drain to that pond.

French drain: do they have to have exit points? I just installed two and did not use an exit point. I thought it just drains out into the soil. For the bigger water issue, I made it extra long?

Do they have to have exit points? I just installed two and did not use an exit point. I thought it would just drain into the soil. For the bigger water issue, I made it extra long.

You could just let it drain out into the soil as long as it's far away from any structures, but beware that burying the pipe and not connecting it to a street sewer or creating a pond, could cause a sinkhole in the future.

My French drain will start in the middle of my lawn and run off into a little stream?

What do I put on the starting end of the pipe to make sure the pip does not block and that I can recover the lawn with soil and turf?

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What stops unwoven geofabric from eventually clogging and becoming in effective?

It seems to be the practice to line a trench with geofabric and then to back fill the trench between the frabric and the pipe with coarse aggregate.What stops the fabric from eventually becoming clogged anyway so that water can't penetrate the fabric and into the drain. Sounds OK when all new but after 5 or 10 years will it still do its intended job?

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If you have problems with any of the steps in this article, please ask a question for more help, or post in the comments section below.


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Categories : Gardening

Recent edits by: Maria Quinney, bladesj, Doug Collins

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