Build a French Drain

The French drain is a simple, yet versatile construction which can be used to drain standing water from problem areas in your yard or basement. The process is fairly simple; it just requires a little preparation and planning, the right tools and materials, and a little DIY know-how.

Steps

Planning and Preparation

1. Look at underground safety. Before building a French drain in a specific area, you must locate all underground cables, pipes or other installations that could make digging dangerous in that particular spot.
   • Check with your municipal or public agencies to make sure you have a free area to construct your French drain. In the United States, you can call the 811 "call before you dig" hotline, which will connect you to your local call center.
   • Also be sure to plan your drainage route so it runs at least a meter away (39 in or about 3') from any walls or fencing, and try to avoid any posts, shrubs or tree roots.
   • Other things you must take into account: the source of the water you will be draining, the greatest amount of flow you can expect to get, and if it is a hazardous or contaminated source.
2. Check for any zoning or runoff issues. Some municipalities have rules on whether you can build or even dig on your own property. Speaking with city and/or county officials and working together is in your best interest for this project. It can be frustrating to have to go through government channels to do work on your own yard, but you must remain patient and polite if you want to get this project done. Stay organized and develop a good relationship with these agencies.
   • In order to get your French drain project going, you may need to contact your local government office or board of officials. It may seem crazy, but even the smallest earth-moving projects can require complicated sign-offs by local government groups. Know the regulations and covenants in your neighborhood before you start planning anything.
   • You will also need to establish whether or not your French drain would cause hardship for neighbors in terms of groundwater runoff. Running excess water onto someone else's land could lead to a potential lawsuit.
   • Ideally the French drain should runoff in a relatively unused section of land, away from any buildings, into sandy soil which allows water to pass through easily.
3. Find a downhill slope. In order to work well, your French drain needs to be constructed on a slight downhill grade. This allows water to drain away from the problem area through the force of gravity.
   • If no natural downward slope exists, you can create a slope by digging progressively deeper as you work your way along the trench. Experts recommend a 1-percent grade for the French drain to be effective. In other words, you should allow for a drop of one foot per every hundred feet of drainage (roughly one inch per ten feet of run).
   • Use landscaping paint to mark out the path of your proposed trench line, then use a couple of stakes, a length of string and a string level to gauge the incline from one end of the trench to the other.
   • If you're not able to figure out the right pitch for your French drain on your own, you can hire a surveyor or other professional to help pin down the right dimensions and placement for your drain. You can still do the work yourself, but you may be more secure in the knowledge that someone else has signed off on the plan.
   • Another option is to rent a transit level (if you know how to use one).
   • Remember that the ditch depth and grade doesn't have to be perfect, but you want to ensure that there are no "bellies" in your drainage, or areas in which water can pool and be held.
4. Gather your tools and materials. In order to build a French drain, you'll need to stock up on a few basic tools and materials. You will need:
   • A roll of water-permeable landscape fabric: this will help to keep your drain pipe clean and avoid clogging by preventing soil, silt and roots from entering the drain. You can also purchase an ADS perforated pipe that has a fabric sock around it.
   • A perforated plastic drain: the diameter of the drain will depend on the extent of the drainage problem and the size of the trench. You can opt for either flexible drain pipe, or for rigid PVC drain pipe (which is more expensive but sturdier and easier to unclog). Make sure the pipe is big enough to carry all of the flow gathered along the run.
   • Washed drainage gravel: the number of bags will depend on the size of your drain. Use an online gravel calculator to get a rough estimate based on the depth and width of the planned trench. Some projects will require more than gravel by the bag. Reach out to sand and gravel companies and inquire about delivery if you need large amounts of rock and/or gravel.
   • Tools: If you plan on digging the trench manually, you will need a spade or digging hoe. Otherwise, you can rent a trenching tool or hire a backhoe operator. Make sure the backhoe can cut a trench that is deep and wide enough for your pipe — most walk-behind trenchers only cut a 4 to 6 inch wide trench.

Building the Drain

1. Dig the trench. Digging the trench is the least complicated step in building a French drain, but it is the most labor intensive! Enlist the help of a family member, friend or neighbor if possible.
   • The width and depth of the drain you dig will depend on the severity of the drainage problem and the digging tool you're using. However, most standard French drains are approximately 6" wide and 18" to 24" deep.
   • Trenching tools will cut wider trenches (which is ideal for more severe drainage issues) and will cut the digging time in half. However, using a trenching tool will also increase your costs as you'll need to pay for the rental and buy additional gravel to fill the larger trench. Trenching machines can be very difficult to control and operate and are extremely dangerous. If you don't know how to use this equipment, it's best to allow a professional to do this or use a hoe. If you do use a trenching machine, ensure that no one gets close to the the chain when the machine is operating.
   • The same goes for hiring someone to cut the trench for you with a backhoe, as backhoes cut very wide and deep trenches and will incur both labor and rental costs.
   • Periodically check the depth of the trench as you dig, to ensure it is consistently sloping downwards.
2. Line the trench with landscape fabric. Once you have finished digging the trench, you will need to line it with the water-permeable landscape fabric.
   • Leave at minimum {{safesubst:#invoke:convert|convert}} of excess fabric on either side of the trench, if not more. Remember that this can always be trimmed later, and that the fabric will be pulled down when you fill the trench with rock. You want to ensure that you have enough fabric on the sides to fold over the drain rock so that it does not contaminate and plug the pipe.
   • Temporarily pin the excess fabric to the sides of the trench using pins or nails.
3. Add the gravel. Shovel approximately {{safesubst:#invoke:convert|convert}} of gravel along the bottom of the trench, on top of the landscaping fabric.
4. Lay the pipe. Place the perforated drain pipe into the trench, on top of the gravel. Make sure the drain holes are facing down, as this will ensure the greatest drainage.
5. Cover the pipe. Shovel more gravel over the pipe, until there is {{safesubst:#invoke:convert|convert}} between the gravel and the top of the trench.
   • Then unpin the excess landscaping fabric and fold it over the layer of gravel.
   • This will prevent any debris from entering the drain, while still allowing any water to filter through.
6. Fill in the trench. Fill in the rest of the trench with the displaced soil. At this point you can finish the trench in whatever way you like:
   • You can lay sod on top, reseed with grass or even cover with a layer of large, decorative stones.
   • Some people even build the drain pipe with a slight curve, so it looks like an intentional design feature upon completion.

Tips

• You may want to spray the installed drain area with water to get it to settle or compact a bit.
• Always work with the following in mind: you need to ensure that the pipe and drain rock are kept clean of soil and debris as best possible, as this can clog and block the pipe.
• Use a good pair of leather work gloves while digging.

Warnings

• Make sure to read up on any special gear to avoid unsafe handling of excavators or other equipment.
• Never use a tamping tool or powered compacting equipment, as it will crush the pipe, causing failure.

Related Articles

• Make a Basement French Drain

Sources and Citations

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