How to Design a French Drain

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A French drain is a simple but effective way to move standing water, whether it's against a house or in a boggy area of the yard. Many people drain their spouting into a French drain to help carry water further away from the structure. Simple to construct, a French drain is just a perforated pipe enclosed in gravel. Instead of being whisked away to the water treatment facility or sewage plant, the water in a French drain is simply diverted and then allowed to soak into the ground under the drain. Because of this, you should use a French drain only to remove clean water and gray water where allowed by law.


How to Design a French Drain
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Pipe Planning

Although a French drain is a simple device, you can run into complicated problems if you don't plan ahead. Before starting your project, check your local zoning laws and ordinances. There are sometimes strict rules about what type of water you can move and where you can put it. You must also make sure that your new drain isn't going to point water at your neighbors or cause problems for them.


Once you know that your drain is legal, call your local utility companies and have them mark any underground wires or pipes for you. French drains need not be deep, but digging even a few inches into the soil can disrupt utility infrastructures.

Digging the Trench

When you know it is safe to do so. dig your drain trench making sure it slopes away from your house and other buildings. Dig a trench that is two feet deep and 10 to 12 inches wide. When creating your trench, remember that wider is better. Over time, the gravel in the bottom of your drain will fill with silt and clog. The more surface area you create, the longer this process takes. Wider trenches are also easier to work with as there is more room to maneuver tools. Twelve inches of width is sufficient but six or eight inches isn't always sufficient.


Building the Drain

When your trench is complete, line it with water permeable landscaping fabric to help stop weeds and roots. Put a two-inch layer of gravel in the bottom of the trench and smooth it flat. Lay a perforated pipe on top of the gravel with the holes down, then cover it with gravel until the trench is three to five inches from the top of the trench. Lay more fabric over the gravel to keep out bits of organic material that could clog the drain. Use topsoil to fill the trench to the height of the surrounding area. Let the soil settle for a week, add more soil if needed and then cover with grass.


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