How to Install a French Drain

Co-authored by Benjamin Hansen

Last Updated: February 5, 2023

A French drain, also called a curtain drain, is made by placing a perforated pipe in a trench that has been filled with gravel. It is a great option if you want to direct surface water away from your home’s foundation to remove surface water or to prevent flooding.^{[1]
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Benjamin Hansen
Licensed Landscape Contractor

Expert Interview. 6 October 2020.} Installing a French drain is a simple job that requires a bit of planning and the right materials. Start by picking a location for the drain that is sloped and the right type of pipe. Then, dig the trench for the drain and put the drain in properly so it can direct water away from your home.

Part 1

Part 1 of 4:

Picking a Location for the Drain

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Look for a spot with a downhill slope close to the problem area. The spot will need to be downhill enough for the water to run away from the problem area. In general, the drain will need to have a 1-2 percent slope drop for every 100 feet (30 m) of length. The slope should start as close to the problem area as possible and move downward towards a draining site.
- For example, if you are trying to prevent surface water from collecting under your patio or in your yard, pick a spot close to your patio or a spot that tends to get very wet in your yard that has a downward slope.
- If you are trying to prevent flooding in your basement, you will need to run the drain around the foundation of your house below the finished flooring and position it downhill into a draining site.
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Check that the spot will drain into a ditch, the street, or a dry well.^{[2]
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Expert Source

Benjamin Hansen
Licensed Landscape Contractor

Expert Interview. 6 October 2020.} A drain made for moving surface water can usually drain into the street, as there will be small amounts of water running through it. A drain made for moving flood water should empty into a ditch or a dry well, as there may be larger quantities of water.^{[3]
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- The spot should slope downward into a clear draining point. If there is not a direct line from the spot to the draining point, you may need to curve the drain so it goes towards the draining point when you dig the trench.
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Pick a spot that is 5 to 6 inches (13 to 15 cm) wide. Make sure there is enough available ground at the location so you can put in a trench this wide. The trench does not need to be wider than 6 inches (15.2 cm), as you do not want to make it too wide.^{[4]
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- If there are any plants in the location that are taking up too much space, you may have to move them to make room for the drain.
Sandy soil will make removing the soil for the trench easier, especially if you plan to do it by hand with a shovel. If you have soil that is thick or rocky, you may need to buy or rent a trench digging tool to make digging easier.

Part 2

Part 2 of 4:

Selecting the Drain Pipe

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Use slotted PVC pipe for a more rigid drain. PVC pipe is a good option if you plan to a run a drain that does not snake around any objects or plants. It creates a strong, rigid drain for a trench with a straight slope downward.
- It also tends to last longer than corrugated pipe and is easier to clean out if it becomes clogged.
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Go for corrugated pipe with slots for a more flexible drain. If you need a French drain that can snake around trees or landscaping, use corrugated pipe. Make sure the corrugated pipe has slots so it can drain properly.
- Corrugated pipe is usually easier to work with than PVC pipe, as it is more flexible and bendable. But this can also make it prone to leaks and tears.
You can buy perforated pipe that has already been wrapped in fabric at your local hardware store or online. This pipe is often sold as an easy install for home improvement projects.
This size will allow water to move through the pipe easily in a steady flow. Pipe that is too narrow can cause the water to pool or trickle too slowly when it rains. Pipe that is too wide can take up too much space in the trench and allow debris to get into the drain.
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Measure the location to get the right amount of pipe. Use a measuring tape to determine how long the pipe is going to be in the trench. Start at the beginning of the trench and measure down to the bottom of the trench.
- You may want to add a few extra inches to the measurement so you have more than enough pipe. You can then cut the pipe down to size when you put the French drain in.

Part 3

Part 3 of 4:

Digging the Trench

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Get the location checked by your utility company to confirm it is safe to dig. Before you dig, call your utility company and ask them to inspect the area for any power lines or underground lines that cannot be touched or moved. They must give you all the clear for you to be able to dig the trench in the location safely.
- You should also consult the city codes for your area to confirm you can dig the trench legally. Most trenches are permissible as long as they are on your land and are not too large or deep. Call your local city building department to double check.
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Dig a shallow trench to redirect surface water. The trench should be 2 feet (0.61 m) deep and 1 to 1.5 feet (0.30 to 0.46 m) across. This will ensure the drain can catch any water on the surface of your property near your home and channel it away to a safe draining spot.^{[5]
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- A shallow trench can often be dug by hand using a shovel, as it is not too much dirt to move on your own.
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Create a deep trench if you want to avoid flooding in your basement. The trench should run around the entire perimeter of your home at footing level. If you are running a French drain around a finished basement, you will need to dig all the way down to access the footing at the basement’s foundation. This is a deep trench that will require significant construction and effort. You may want to rent trench-digging tools to make the job easier.^{[6]
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- You may also need to remove any landscaping or walkways that are around the bottom of the house to put in the trench.
- If you want to avoid digging a trench this deep or the area does not have enough slope, you can run a pipe down to the basement to direct water into a basin and use a sump pump to lift out the water. This is a different method than using a French drain.
Put the stakes on either side of the trench every couple of inches to mark the dimensions of the trench. Then, tie a string around the stakes, forming two long lines of string on either side of the trench. Follow the grade marked by the strings as you dig to ensure the trench is the same dimensions all the way down.
Start at the top of the trench and dig your way down. Check the grading regularly as you dig to ensure you are creating the right dimensions. You may find this process easier if you ask friends or family to help you dig, especially if you are digging a long trench.
Look into renting a trench digger at your local hardware store or buy one, especially if you plan to do deep digging in your yard in the future. A trench digger is usually a must if you are digging a deep trench around the perimeter of your home, as it will make the process much faster and easier.^{[7]
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Scoop the top soil on one side of the trench so you can put it back on the trench when it is completed. Then, deposit the subsoil in a wheelbarrow so you can move it away easily. Use the subsoil to fill holes or area in your yard. You can also put the subsoil in a container or in the road so you can bring it to the dump or to your local gardening center later.^{[8]
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Line the trench with water-permeable fabric. Place one layer of water-permeable fabric on the bottom and sides of the trench. The fabric will prevent dirt from getting into the gravel and help water move through the drain.
- You can get water-permeable fabric, sometimes called landscaping fabric, at your local hardware store or online.
Spread a light load of gravel with a shovel over the top of the fabric. This will help the corners of the fabric warp around the gravel, securing it in place.

Part 4

Part 4 of 4:

Putting in the Drain and the Gravel

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1
Wrap the drain in water-permeable fabric. For an extra layer of protection, you can wrap the pipe you are using for the drain in one layer of the fabric and secure it with tape. You can also use a specially made water-permeable sock or cozy that fits over the pipe.^{[9]
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- If you are using pipe that already has water-permeable fabric wrapped around it, you can skip this step.
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Place the drain with the drainage holes face down in the trench. Lay the pipe in the trench so the slotted holes face downward, as this allows the water to flow through the pipe into the draining site. Make sure you have enough pipe to fill the length of the trench. The pipe should sit snugly in the gravel.
- If you are running the drain by any trees or shrubs with deep roots, use a section of pipe that does not have any slots in these spots. This will prevent the roots from getting into the pipe and clogging it up.
Use gravel that is 0.5 to 1 inch (1.3 to 2.5 cm) in size to cover the drain and fill the trench. Put the gravel in with a shovel, making sure it is evenly distributed in the trench.
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Place one more layer of water-permeable fabric, followed by the top soil. Lay the fabric on top of the gravel to protect the drain from debris and to help it better absorb water. You can then shovel the top soil on top of the fabric to cover it.
- You can also put sod on top of the topsoil to hide the drain, though this is not required.
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Test the drain to ensure it flows downward to a draining spot. Check that the French drain works properly by putting surface water by the top of the drain with a garden hose. Note if the drain then draws the water from the wet spot and deposits it to the draining site.
- Alternatively, you can wait for it to rain to see if the drain will work properly.
- If the drain does not collect the water properly, you may need to check that the slots on the drain are facing downward, rather than upward.
- If water does not flow through the drain properly, there may be debris or a blockage in the drain that needs to be removed for it to work.

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Benjamin Hansen
Licensed Landscape Contractor
Benjamin Hansen is a Landscape Contractor and the Owner of Artscape Gardens, a boutique landscaping company in Los Angeles, California. With over 12 years of experience, Benjamin specializes in transforming properties into aesthetic, functional, and drought-tolerant oases. Benjamin uses color scheme, dimension, and water conscious spaces to inspire the design and installation of soft scape, hardscape, patios, pathways, irrigation, drainage, fencing, concrete, lighting, and electrical work. Artscape Gardens covers all areas of the C-27 landscape contractor classification.

Benjamin Hansen

Licensed Landscape Contractor

Expert Answer

What's important is that the water is properly diverted away from the foundations of the house.

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