What is a French Drain?

french drain

Is a French drain necessary?

Your landscape contractor has told you that your lawn needs a French drain. So, what is a French drain and why do I need a French drain? Well, the first thing you need to know French Drain is named after a person, not the country or food item. It was Henry Flagg French, an American, the president of Massachusetts Agricultural College, that invented the French drain. 

This landscaping tool sounds exotic, but it is common and in some landscaping situations, it is an important tool that removes water from an area that doesn’t have good drainage.  It is used a lot in fields and today, it is common around homes with landscaping issues from standing water. Essentially, a French drain is underground gutter system for your yard and moves water from where it won’t drain and causing problems.   

Water runs downhill naturally, so when humans build houses or retaining walls, it tends to get the way of that natural process. A French drain is an effective and simple to reroute water from a crawl space, driveway, foundation, or retaining wall.  When water isn’t running downhill or the bottom of the hill is your home and landscaping. 

When should you use a French drain?

How do you know if your landscaping and yard needs a French drain?  If you are experiencing any of the following issues, you should talk to a landscaper about installing a French drain: 

  • Crawl Space Floods: If the crawl space of your home is flooding, having a French drain installed will send that water away from your home.  Leave it as it is, you are leaving your home in danger of being damaged, mildew and mold building up under your house, and more. 
  • Soggy Yard or Driveway Washed-Out: If your yard takes days to dry out after a rain before you can mow, or you have to rake rock back into your driveway after a good rain, a French drain could be the answer to your problems. Keep your lawn healthy and driveway rock where it belongs.
  • A Retaining Wall: If you have a retaining wall or plan on building one a hillside or slope, the first thing you should do is have a French drain installed. With this installed behind the first course of the retaining wall, it will keep the water from building up at the bottom of the wall and draining toward your home.

Do French drains really work?

Like anything, A French drain can only work as good as it is installed. French drains require a perforated pipe, a trench, and geotextile fabric with gravel. If the slope isn’t adequate, a French drain won’t work as well as intended, a factor that is overlooked too often, giving French drains a bad name.   An adequate slope is no less than two feet lower for every 100 ft of pipe. A four inch drainpipe should be covered with two inches of soil once it is in place. This will allow water across the surface to drain and the French drain to work properly. 

How long do French drains last?

A professionally installed French drain can last up to forty years. However, there are two factors that can shorten that expected life cycle: 

  • The French drain becomes clogged with dust, mineral, and grain particles from the soil that surrounds the drain. This can be minimized when the French drain is installed by putting twelve inches of crushed stone over the drain. 
  • The French drain is incorrectly installed, common when installed by contractor that isn’t experienced installing French drains, usually not deep enough or the slope isn’t enough. 

French drains are affected by the environment and can wear out over time. Simply having it rebuilt and adjustments made will give you another 40 years of water moving service. 

How deep should a French drain be?

As shallow as eight inches and as deep as two feet. The depth will depend on the goal intended as to where the water is a problem and where you need it redirected.  The base of a retaining wall will likely require a French drain to be deeper than it would be around the foundation of your home.  An experienced landscaper will have the knowledge to determine the proper depth. In some rare cases where a basement or crawlspace keeps taking on water and the French drain isn’t being as efficient has hoped, a sump pump may need to be installed. 


What’s the difference between a French drain and trench drain?

A drainage system is more than just digging holes. There are French drains and Trenches, both are effective ways in moving water, but they are different. A French drain is below the surface whereas a trench drain is on the surface. 

  • A French drain is a gravel-filled trench that has a perforated pipe on the gravel with a permeable fabric along the bottom of the trench to keep any roots intruding. It then siphons the water down and away from where it isn’t wanted.  
  • A trench drain is an above-ground method of draining water by way of embedded materials. A long and narrow trench is dug and then a grate is installed over that trench. 

You’re likely asking, “Do you have to have a landscaper or other professional install a French drain, or Can I install a French drain myself?”, and the answer is yes. With all the online videos and the big box stores offering assistance, some even offer classes, any homeowner with DIY motivation and tools can install their own French drain. Call 817-400-7625 today!