A French drain is a simple yet effective way of redirecting water from an area with poor drainage. It’s a trench with a perforated drain pipe installed to divert water from your home or another area lined with gravel or rock.
French drains are beneficial for several reasons. They effectively control water runoff and prevent flooding, reduce the risk of basement flooding, and help prevent erosion around your property. In addition, French drains can help to keep foundations dry and free from water damage.
To install a French drain, you must dig a trench, lay down fabric mesh, line it with gravel, install a perforated PVC pipe, and refill the trench with soil and/or gravel. Keep reading for a step-by-step guide to installing a French drain and fixing your property’s drainage problems.
- Installing a French drain yourself is possible but labor-intensive and time-consuming.
- Call 811 a week or two before you start your project to get your buried utility lines marked. This prevents unfortunate accidents and injuries.
- When you dig the trench and lay the gravel for your French drain, ensure you have 1 inch of a downward slope for every 10 feet of pipe run.
How To Install a French Drain (In 7 Steps)
The difficulty of installing a French drain will depend on the size and complexity of the project. A homeowner can complete straightforward installation in hours, while larger installations may require more time and greater expertise. It’s important to consult with an experienced contractor or plumber if you are unsure about your ability to install a French drain properly.
Use the seven steps below to install a French drain near your home and stop drainage issues.
Step 1: Dig a Trench
To begin your French drain installation, you’ll need to dig a trench in the area where you plan to install the drain. The trench size should be larger than the pipe placed inside it, so make sure to measure accurately before digging. Create an angle when digging your trench so that it slopes away from existing structures or areas prone to flooding.
Step 2: Add Weed Barrier and Gravel
Once the trench is dug, you’ll need to line the bottom with a weed barrier or water-permeable fabric mesh. Leave sufficient excess fabric to wrap around the pipe and an additional two inches of gravel once the pipe is installed. This will help prevent any soil or other debris from clogging your pipe. Then, fill the trench with about two inches of gravel. Spread it evenly so water can flow freely through the pipe.
Step 3: Install Drain Inlet and Pipe
Before you install the pipe, you need to install a drain inlet (a small catch basin) that works for the diameter of your pipe. This will allow surface water to enter the French drain and flow away from your home’s foundation or property. Then install your drainage pipe.
Lay the pipe on top of the weed barrier and gravel with the perforations facing the bottom of the trench. Connect the top end to the inlet.
Step 4: Cover with Gravel
Once the pipe is installed, cover it with two more inches of gravel.
Step 5: Wrap the Remaining Fabric Around the Pipe and Gravel
Once you’ve covered the pipe with gravel, wrap the excess filter fabric around the pipe and gravel. This will help prevent any soil or debris from entering and clogging up your French drain.
Step 6: Cover With Remaining Gravel
Once you wrap the fabric around the pipe, slowly fill the remaining space in the trench with gravel. Make sure to spread it evenly so water can flow freely through the French drain.
Step 7 (Optional): Add Topsoil, Mulch and Landscaping
You can either fill the trench to ground level with gravel or leave room to complete filling it with topsoil or mulch and install landscaping, if you prefer, to add aesthetic value and prevent erosion.
What Materials Do You Need to Install a French Drain?
To install a French drain, you’ll need the following materials:
- Shovel or trencher digger
- Level, wooden stakes and string (to determine slope)
- Fabric mesh
- Perforated pipe
- Small catch basin
- Optional: dirt or topsoil
- Optional: landscaping materials (mulch, grass, add/or small plants)
The amount you need and the length of the pipe will depend on the size of your French drain project.
Cost To Build a French Drain
French drain costs vary by size, but here is a cost estimate for the materials you need to build one French drain with a 6-inch diameter, 10-foot-long perforated drain pipe:
|Two wooden stakes||$10|
|Fabric mesh (landscaping fabric)||$50|
If you don’t have a shovel and level already, you can expect to pay $30–$100 more to complete your French drain project.
How Do You Prepare Your Lawn to Install a French Drain?
Make sure you choose the correct location for your French drain. You need to install it where the water is pooling for it to work properly. So keep that in mind as you plan your installation and how you want it to drain.
Calculate the amount of gravel needed depending on the size of the drainpipe you’ll be using, and ensure there is enough slope in the area to allow for adequate drainage. If not, you may need to dig out a deeper trench. Then, mark out the area for your French drain using stakes and strings so that you can clearly see where to dig. Finally, remove any grass, plants, or debris from the area before digging.
Before digging your trench, lay out tarps to shovel the dirt onto. This will help protect your lawn. You can also use tarps to stage gravel and topsoil you will use to backfill the French drain.
Today’s Homeowner Tips
To ensure you install your French drain properly, you should begin with proper preparation and planning. Before you dig, call 811 to have a technician come out and mark any buried utilities (electrical, gas and other lines).
How To Measure the Slope of Your Yard
As discussed above, French drains need a 1% downward slope to drain properly — a decline of one inch for every ten feet of pipe. Your yard may naturally have this degree of downward slope (or greater).
To find out if it does, measure the slope of your lawn with this simple method:
- With two wooden stakes at least 36 inches long, mark the stakes up to 36 inches at 1-inch intervals and number the markings. You’ll have made giant “rulers.”
- At the top and bottom of your slope, drive the stakes the same distance into the ground (between six and 12 inches) at the top and bottom of your proposed French drain location.
- Tie a string (make sure it’s taut) between the top and bottom stakes. The string should be tied at the first visible measurement marker above the ground on the top stake. On the bottom stake, it should be tied so that the string is level (use a carpenter’s level to be sure).
- Measure from the ground up to the string at both stakes. Subtract the top stake measurement from the bottom stake measurement to get the rise of your slope.
- Next, measure the length of the string to get the run of your slope. Then divide the rise by the run and multiply the result by 100 to get your percentage slope.
If the result is 1% slope or greater, you should dig the trench for your drain at the same depth for the entire length. If the result is 1% or less, you can compensate for the lack of slope by digging your trench progressively deeper from top to bottom, but you’ll need additional gravel and/or topsoil to fill the additional space.
How to Calculate the Amount of Gravel You Need for Your French Drain
To determine how much gravel you need for your French drain project, use the ratios below (for a trench depth of 12 inches:
|Gravel Needed||For a 4-inch drain pipe||For a 6-inch drain pipe|
|Gravel per 1- x 1-foot trench area||0.72 cubic feet||0.6 cubic feet|
So, if you have a 10-foot x 1-foot trench and use a 4-inch pipe, you need 7.2 cubic feet of gravel (10 x 0.72). If you use a 6-inch pipe, you need 6.0 cubic feet (10 x 0.6).
How Do You Maintain a French Drain System After You Install It?
After installing your French drain, perform routine maintenance to keep it functioning properly and ensure that water diverts away from your home.
Inspect the French drain periodically for clogs, and clear any accumulated debris in the pipe. Also, watch for any erosion or soil displacement around the trench, which can cause blockages. If you notice any of these issues, address them immediately. Follow these maintenance tips:
- Regularly check the inlet and outlet (if there is one) of the drain to ensure that it isn’t blocked
- Flush any debris every few months if necessary
- If your drain breaks or comes apart, you may need to dig it up and reassemble it. This is easier if the drain is covered with only gravel and not topsoil and grass too.
Finally, it’s important to remember that a French drain system must be kept functioning properly to do its job. If you notice that water is not draining away from your home as expected, it may be necessary to add additional gravel or regrade the slope of the trench.
To repair your French drain, first identify the problem. If the drain is clogged, use a plumbing snake or a pressure washer to clear any debris (you’ll need to access the beginning point of your drain for this). You must replace the damaged sections if the drain has holes or cracks. Dig up the area around the damaged section, remove the old pipe, and install a new one. Use gravel to create a stable base for the new pipe and cover it with gravel. If the problem is with the slope of the drain, you may need to dig up and reposition the entire drain to ensure proper drainage. Sometimes, hiring a professional to repair your French drain may be best.
How To Avoid Underground Utility Lines When Digging a Trench for a French Drain
Avoiding underground utility lines when digging a trench for a French drain is crucial for safety and avoiding costly damages. The first step is to contact your local utility companies by calling 811 to mark underground lines before starting digging. This service is free, but it may take a week or longer after you call for a service person to visit your property to mark the lines.
Dig your trench at least 18 inches away from 811 markings (typically marked with small flags and spray paint) to ensure you don’t cut into them and risk severe damage to your home and injury to yourself.
DIY vs. Professional: Should I Hire Someone to Install My French Drain?
Whether to hire a professional or do it yourself to install your French drain depends on your level of expertise and the complexity of the task. Installing a French drain involves digging a trench, laying down a drainage pipe, covering it with gravel, and backfilling the trench. This is labor intensive, especially if your French drain needs to be long.
If you have experience with excavation, plumbing, and drainage solutions and have the necessary tools, you may be able to handle the job yourself. However, it’s best to hire a professional if you’re not confident in your abilities or if the installation requires heavy machinery or extensive earth moving.
Professional installers have the experience, skills, and equipment to ensure that the French drain is installed correctly and will function properly for years. However, hiring a professional will cost you more money. Ultimately, it’s important to weigh the costs and benefits of each option and choose what’s best for your situation.
Final Tips When Installing a French Drain
Installing a French drain can be labor intensive, but most homeowners can do it as a DIY project with some planning and the right tools. To begin, you’ll need to identify where the drain needs to be installed and mark out the area for digging. It’s important to remember that French drains should always be installed with a slight downward slope so water can flow away from your home. When digging, take extra care to avoid any underground utility lines. Lastly, you’ll need to fill the trench with gravel and a drainage pipe.
If you need a large French drain (over 10 feet long), have to dig through hard soils like clay, or don’t want to perform difficult labor, consider hiring a professional to install the drain for you. Whether you install it yourself or hire it out, perform preventative maintenance after you build your French drain to ensure it lasts for as long as possible.
FAQs About French Drains
What type of gravel should I use for a French drain?
The type of gravel you should use for a French drain depends on the size and purpose of the drain. Generally, professionals recommend medium-sized gravel with a diameter of about ¾ inch to 1 inch. This size allows for good drainage and prevents the gravel from being too heavy or compacted. Avoiding fine gravel or sand is important, as it can clog the drain and reduce effectiveness. Additionally, some experts recommend using angular gravel instead of rounded gravel, as the angular edges help to interlock and create a more stable and effective drainage system.
How do I know if my French drain is working properly?
To know if your French drain is working properly, you should first check for any excess standing water in the area where the drain is installed. If there is no water, the drain is doing its job of diverting water away from the area. You can also check if the drain is clogged by directing water into the drain with a garden hose and observing if the water is flowing freely or not or by observing it during heavy rain. If the water is flowing freely, the drain is not clogged and working properly.
How do I install a French drain around my foundation?
Installing a French drain around your foundation can be a great way to prevent water damage and flooding in your basement or crawl space. The first step is to dig a trench around the perimeter of your foundation, making sure it slopes away from the house. Then, follow the same 7-step guide above.
What’s the best way to dig through clay soil when digging a French drain?
The easiest way to dig through clay is with a trenching machine (or trencher), a heavy-duty machine used for digging trenches in the ground. Most hardware and landscape supply stores have trenchers available to rent.
Another useful method to dig through clay soil is to use a pickaxe or mattock to break up the soil and remove large clumps. Working in small sections is important, breaking up the soil and removing it with a shovel. Taking frequent breaks is essential, as digging through clay soil can be physically demanding.