The term “French drain” is often confused with other systems, such as surface or curtain drains. Unlike those, a French drain collects subsurface water, directing it away from problem areas using gravel, geotextile fabric, and a perforated pipe.
As a landscape designer, I’ve designed and installed French drains for homeowners, and with insight from a landscaping expert, we’ll break down how they work, their key components, and how they differ from surface drains and dry wells.
If heavy rain has left standing water in your yard, killing your grass and making the space unusable, it’s time to contact a LawnStarter landscaping pro. They can restore your healthy lawn and give you back your private oasis.
How a French Drain Works
A French drain is an underground drainage system that uses gravity to guide excess groundwater (subsurface water) away from saturated areas through an underground pipe. Its sloped trench allows water to flow naturally toward a safe exit point, preventing pooling around your home and yard.
See Related: How To Install a French Drain in Your Yard
Components of a French Drain and What They Do
Now that we’ve covered the basics of a French drain and how it functions, let’s focus on the 4 essential components and how they work as part of this subsurface drainage system.
Trench
The trench is a ditch that uses slope and gravity to direct water toward the outlet. Its depth and width depend on the frost line and the space needed for the gravel, pipe, and fabric.
Non-woven geotextile fabric
According to Damon Abdi, assistant professor of landscape horticulture at Louisiana State University, the trench should be “lined with a fabric to allow water to move through and to exclude soil from clogging the pipe.”
DOT-certified non-woven geotextile fabric is more effective than traditional plastic and woven landscape fabric, which is designed more for weed control and structural support.
Gravel
In a French drain, gravel is key: It lines the bottom of the trench to hold the pipe and filter sediment. It also fills the space around and above the pipe “to allow easy water flow,” Abdi says.
Perforated pipe
The pipe collects and moves water to the drainage point. Use either corrugated or PVC pipe, but make sure it’s perforated. This lets water enter and exit along the pipe’s entire length, unlike a box drain that collects water at a single inlet.
Corrugated pipe is flexible and easier to bend around curves, while PVC is rigid. Choose pipe size based on how much water the drain needs to handle.
Catch basin (optional, but frequently used)
A catch basin is connected to the main French drain pipes and usually consists of a grate on the surface with a collection box underneath to help prevent sediment from running into the pipe.
Catch basins are used to collect water from high-volume areas: gutter downspouts, off of a paved area, or area in lawn with heavy standing water.
Riverstone (optional)
Smooth riverstone adds a natural, decorative finish once soil is backfilled if you don’t want to plant grass seed on top.
Skip this step if you prefer to cover the drain with “turf over the top for a more discreet look in the middle of the lawn,” Abdi says. You can also leave the gravel exposed for a clean, textured look.
How French Drains are Different From Other Drainage Solutions
Like French drains, trench drains and dry wells also manage water. The key difference lies in how they do it.
According to Abdi, “A French drain is a subsurface drain, a trench drain is a surface drain, and a dry well is less so for the conveyance of water than it is for holding water and releasing it to the surrounding soil.”
Surface Drains
Purpose: Surface drains are “designed to evacuate surface water rapidly,” Abdi says.
How it’s different from a French drain: Primarily designed to drain surface water instead of subsurface water (as a French drain is designed to do); often uses an exposed grate for water to enter
Pro Tip: Trench drains, channel drains, and curtain drains are all types of surface drains.
Dry Wells
Purpose: “A dry well is essentially a subsurface reservoir where water can be directed to and held as it seeps into the surrounding soil,” says Abdi.
How it’s different from a French drain: Designed to hold water to be released slowly, rather than directing it to be deposited elsewhere, as a French drain does. However, Abdi says, “A dry well (also) can be connected to the low point of a … French or trench drain to collect and hold excess water.”
Interior French Drains (Basements)
Purpose: Interior French drains are often used in basements that flood, directing water that seeps through walls or floors into a perimeter trench connected to a sump pump.
How it’s different from a French drain: Besides being indoors, the only difference is that interior French drains may use a sump pump to collect and drain the water.
My experience: In my own home, we have a modified version of an interior French drain: A small trench cut into the concrete floor channels water to the sump pump, which then carries it outside to the driveway.
FAQ
If you notice these issues, a French drain may be a suitable solution:
• Persistent water pooling in the yard
• Wet basement
• Soil erosion near the foundation
You can find French drains near building foundations, slopes, areas with standing water, and the lower elevations of a yard.
See Related:
• 12 Ways to Get Rid of Standing Water in Your Yard
• 7 Ways to Improve Drainage in Your Yard
Homeowners can expect to pay an average of $5,000 for professional French drain installation. However, the cost of a French drain ranges from $1,650 to $12,250, depending on the drain’s length, depth, and other factors (like unexpected tree root excavation for hidden roots).
Yes, you can DIY a French drain if you’re comfortable digging below your area’s frost line and have moderate DIY skills. In colder regions with deep frost lines (44+ inches) or where water is collecting close to the foundation or coming into the home, it’s better to hire a company that specializes in drainage systems.
Hire a Pro to Install a French Drain
If your yard is a small pond and you think a French drain will help divert the water, consider hiring a LawnStarter landscaping pro near you. They have the expertise and knowledge to save you time, effort, and potential errors while giving you peace of mind.
Sources
- “6 Types Of Drainage Systems For Your Home & Yard.” Simple Lawn Landscaping.
- Damon Abdi, assistant professor of landscape horticulture at Louisiana State University, Hammond, LA. Personal interview.
- “Drainage Swales.” Chicago Department of Water Management.
- “French Drain System Installation.” By Pavel Sidorov, waterproofing and drainage expert. MT Drains and Plumbing.
- “French Drain vs. Trench Drain: Comparison of Types and Variations.” Pipe Express Inc.
- “What is a Dry Well Used For?” By Michael Micheletty, drainage expert. Alpha Environmental.
- “Why Corrugated Pipe is Used Versus Smooth Wall or Hard Pipe When Building a Michigan French Drain?” By Robert Sherwood, French drain expert. French Drain Man.
Main Photo Credit: French drain. Photo Credit: Shutterstock
