If your lawn looks like a lake after it rains, you’re in need of a drainage solution. Standing water can harm your grass, home’s foundation, and become a breeding ground for pests, but a French drain is a simple solution for your water worries. This guide will show you how to install a French drain yourself, step-by-step.
- What is a French drain?
- How to install a French drain in 6 steps
- FAQ about installing a French drain
- Get help from a pro
What is a French drain?
A French drain might sound like it belongs in the Palace of Versailles, but it’s nothing fancy. It’s essentially a dressed-up trench that uses a mild slope to carry water from one place to another. The water filters from the surface, is carried underground, and deposited at an exit point.
Components of installing a French drain:
- 18-inch deep trench
- Perforated pipe
- Landscaping fabric
Now that we get the big picture, let’s dig into the details of French drain installation.
How to install a French drain in 6 steps
1. Choose your exit point
You might know where you don’t want water, but what about where you do? Choosing an exit point for your French drain is an important first step. Do you want to collect the water for later use or help filter out contaminants before it reaches the waterways?
There are a few different options for exit points depending on your interest:
- Municipal storm drain: This is a public drainage facility, like a curbside storm drain.
- Dry well: A dry well is a structure that moves surface water underground. It’s just what it sounds like – a well with no water. Dry wells are usually 30-70 feet deep and either filled with gravel or left empty.
- Rain barrel: A rain barrel collects stormwater for later use on lawns and gardens. You can buy one from a home and garden center or sometimes from your local government. You’ll need to connect a sump pump to the end of your French drain system to propel the water into the barrel.
- Rain garden: A rain garden is a garden planted in a water collection area, such as a depression in your landscape. Rain gardens feature plants that don’t mind sitting in soggy soil.
As water sinks into the soil of a rain garden, the plants’ roots filter chemicals out of the water. Connecting your French drain to a rain garden is only suitable if your area experiences medium to low annual rainfall (a rain garden isn’t enough to handle heavy water runoff).
2. Dig the trench
Important safety tip: Before you get started digging your trench, put down the shovel and pick up the phone. Ring the Call Before You Dig hotline at 811 to get information from your city about where underground utility lines are located. Once you know your plan for the trench won’t include any shocking surprises, you can get to digging.
Digging your trench will go much faster if you enlist the help of your friends. Remember that time you helped your friend carry that sofa to their new place? This is the time to call in the favor.
What you can use to dig your trench:
- Trencher rental
For French drains, the trench should be at least 18 inches deep at the shallowest point and 9-12 inches wide. For gravity to carry the water to the desired exit point, there needs to be a slope of at least 1%. That’s about a 1-inch drop per 8 horizontal feet. Every 8 feet, insert a stake 1 inch lower than the previous one. This will be your guide.
- Lay tarp along the sides of the trench so you can easily move the soil after you’re done.
- Keep any equipment away from the sides of the trench.
- Don’t stress the slope too much – you can easily move the gravel to adjust the slope of the pipe later on.
3. Line the trench with landscape fabric
In this section, we’ll cover:
- Why you should line your trench with landscape fabric
- What type of landscape fabric to use
- How to install it
Landscape fabric (also called geotextile fabric) keeps soil and plant roots out of the French drain. Because the pipe you’ll put in is perforated, it’s at risk of being clogged by adventurous plant tendrils, which could ruin all your hard work.
There are two types of landscape fabric: woven and nonwoven. For French drains, look for a nonwoven fabric. Water flows easily through this type. Choose a medium weight fabric (4-6 ounces). Textiles in this category are great for controlling erosion and facilitating drainage.
Installing the landscape fabric is straightforward. Lay enough landscape fabric to cover the bottom and sides of the trench. You can use landscape fabric staples to secure it in place as you’re laying the gravel.
4. Fill with gravel
Your next step is easy: Pour a layer of gravel on top of the landscape fabric. Gravel allows water to filter out through the pipe into the soil and improves drainage. Your layer should be around 3 inches deep.
What kind of gravel should you use for a French drain? Avoid pea gravel and crushed rock and opt for round, washed rock ½-1 inch across. You don’t want the gravel to clog your pipe or impede the flow of water.
How much gravel do you need for a French drain?
Gravel is usually available in cubic feet. To figure out how many cubic feet you’ll need for your French drain, multiply the length by the width by the depth.
For French drains, the depth will be 3 inches, which is 0.25 feet. For example, if your French drain will be 30 feet long and 1 foot wide, you would use: 30 x 1 x 0.25 = 7.5 cubic feet.
If you’re looking at gravel that comes in pounds, you’ll need an additional step. 1 cubic foot of gravel is equal to about 96 pounds, so you’ll multiply your cubic feet by 96 to figure out how many pounds you need. For the example above, you’d multiple 7.5 by 96 to get 720 pounds of gravel.
5. Add the pipe
After all that prep for your French drain, it’s finally time to install the pipe itself. The pipe needs to be perforated to allow water to drain underground as it’s carried. This prevents a messy spout at the exit point.
The actual installation is easy. All you need to do is situate the pipe on top of the gravel bedding with the perforation holes facing the ground (otherwise, the top layer of crushed stone and soil will clog the pipe).
What kind of pipe should you use for a French drain? Look for a 4-inch diameter pipe. Any smaller and you risk clogs. Skip corrugated pipes and go for a rigid PVC drain pipe for durability and crush resistance. You can buy these pre-perforated, or drill holes in a zigzag fashion every 2 inches.
6. Add finishing touches
After the pipe is installed, it’s time to beautify your French drain so it blends seamlessly into your landscape. You have a few options here for coverage. You can use crushed rock and leave it at that, or you can add larger rocks of different shapes and sizes for a look akin to a dry stream.
If you want an even more blended look, cover with about a 3-inch layer of gravel, then a layer of landscape fabric, and finally a layer of topsoil. Add ground cover plants to conceal your new drainage system in green. If you cut a section of your sod and removed it to dig the trench, you can re-cover the area with that sod too.
FAQ about installing a French drain
A French drain has a relatively quick installation process compared to other systems. Other benefits of French drains include getting rid of standing water, controlling erosion, and minimizing toxic rainwater runoff.
Professional installation can take as little as 6 hours. If you’re doing it yourself, expect to spend the whole weekend.
In total, DIY French drain installation costs about $270-$350 for a 20-foot drainage system, including trencher rental. That comes out to $13.50-$17.50 per foot.
Here’s how that cost breaks down:
–Landscape fabric: $20-$50 for 20 feet of nonwoven landscape fabric
–Gravel: Around $50 for 5 cubic feet of gravel.
–Pipe: $100-$150 for a good quality 4-inch diameter, 20-foot long PVC pipe
–Trencher rental: Around $100 per day
For professional French drain installation, add $20-$25 per linear foot for labor costs.
Regular maintenance is key to prolonging the life of your new French drain. It’s important to clean it once a year to remove any buildup of debris. While you can rent an electric sewer snake to clear it yourself, it’s easier to hire an expert because it requires multiple people to operate.
The short answer is no. Your drainage system can become overwhelmed with water during a heavy storm, washing away gravel and clogging the system.
However, there’s a solution: If you need drainage for your downspout and want to utilize a French drain, simply install a catch basin between the downspout and the drain. A catch basin will prevent flooding and acts as an easy-to-clean collection point for leaf debris.
Get help from a pro
If the French drain installation process seems too tough to take out by yourself, or if you run into a problem with power lines or a (literally) rocky foundation, it’s best to call a landscaping professional.
You might have French drain installation covered, but what about the rest of your lawn? A Lawn Love team can take care of yard maintenance like mowing, seasonal cleanup, and plant installation.
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