What is a French Drain System?
A French drain, which may also be called a curtain drain, perimeter drain, weeping tile, or agricultural drain, is a gravel-filled trench that includes a perforated or slotted pipe. These drains are used to direct surface water or groundwater away from a specific area, such as a home's foundation.
French drains direct surface level water toward the lowest point and allow it to seep through the surface level gravel into the drain. This gravel also blocks the passage of excess debris. The water is then collected in the perforated pipe, running at the base of the drain, and directed away from the home and toward a more suitable area. Infiltration French drains differ from typical surface drains because they collect water over the entire length of the drain instead of one particular spot. French drains can also prevent water from collecting and pooling in specific areas, saturating the ground below, which may lead to water problems at the surface or below. Instead, this water is directed to a more desirable location such as a dry well or an area of your choosing. Subsurface drainage systems have been in use for centuries, helping with everything from controlling agricultural runoff to providing yard drainage. They take many forms, but are all similar in design and function to the traditional French drain system.
How Does a French Drain Work?
Remember that liquid always seeks out the lowest point it can reach along the easiest path, readily moving into empty pockets in loose soil. That's the secret to a French drain: It provides a reliably easy path, creating a sunken channel that encourages water to percolate out of the surrounding soil and flow along a smooth course. Gravity is essential for a French drain to function properly, as it first forces water down from the surface and out of saturated soil, then pulls it along the downward-sloping pipe to the desired discharge point.
French Drain Pipe Characteristics
One of the most common pipe materials used to create a French drain is plastic because of its durability. There are two frequently chosen pipe variations: corrugated and PVC. Both are lightweight, but corrugated pipe can be flexible, while PVC is stronger and more rigid. Regardless of what the pipe is made of, it must be slotted or perforated at regular intervals to allow water to enter and flow through the system.
Another option for areas that require French drain pipe installation is the EZ flow system, which is a pipe that comes already surrounded by an aggregate and fabric mesh. The drain pipe itself is made of high-density polyethylene, and is corrugated and perforated. French drain pipe alternatives such as this one are flexible and come in pre-set lengths, typically of 5 or 10 feet each.
Considering other dimensions is also integral to installing French drain piping, as the pipe's diameter will impact how much water can flow through. A 4-inch diameter perforated French drain pipe is likely adequate for most residential applications, but areas expected to experience a good amount of water collection and heavy soil saturation may require a larger-diameter pipe. Commercial or agricultural uses may also require a larger-diameter perforated pipe for French drain systems.
French Drain Applications
French drains are used nationwide by residential, commercial and municipal property owners who face drainage issues that may damage their homes, buildings and property, or limit the usability of lawns and landscaped areas. Since water flows downward along paths of least resistance, it can collect against sunken walls and barriers, where it can degrade the material over time. Then, even a hairline crack can allow the water to gain entry where it isn't wanted, destroying property, creating health hazards, and more. Seepage into a below-ground room, such as a basement or even a crawlspace, can be anything from a nuisance to a major problem.
A French drain is useful in solving drainage problems for:
- Building foundations, basements, and crawlspaces
- Lawns and landscaped areas
- Sports fields, playing fields, and playgrounds
- Hardscape patios and driveways
- Retaining walls
- Any area subject to surface or subsurface saturation
An easy way to site a French drain is to watch where water pools—especially if it sits for hours or days—after a rain. Clay soil can contribute to this problem, as it holds water well. Clay can also clog a French drain system by filtering fine particles into the aggregate, where the particles fill in gaps and prevents water from getting through.
To help you make an informed decision about whether this method will serve your needs, here are some common drainage problems homeowners face, and how a French drain can reduce or eliminate those problems.
Flooding in your backyard. If heavy rains have left your yard with an unwanted water feature or the spring thaw has saturated your yard, a French drain can help. Placing a French drain in this wet region allows the drain to collect unwanted water and redirect it to a safer location, giving you back your green space.
Damage to your outdoor patio. Your patio is a great source of pride and a meeting place for family and friends, but excess water can damage the area, deteriorate the pavers, and also create a breeding ground for mosquitoes, ruining your ability to spend time outdoors. A French drain can work as a shield, collecting water before it reaches the patio and diverting it away. This will eliminate the standing water that mosquitoes need.
Damage to the foundation and low-level areas like your basement. Check the walls in your basement. If you notice a musty smell or wet floor, you need a French drain immediately. A French drain can stop this water from ever reaching your home, protecting your basement from flooding and your home's foundation from incurring additional damage.