7 French Drain Mistakes That Are Ruining Your Lawn (and How to Fix Them Fast)

An important component in a yard drainage system, a French drain removes standing water from the yard and house foundation by providing the water with a path of least resistance. 

Though a French drain is composed of just three elements—perforated pipe, filtration fabric, and gravel—it’s easy to make costly, time-consuming mistakes when installing the drain.

Learn the main French drain mistakes that DIYers make and how to avoid them.

Wrong Filtration Fabric

A common mistake when installing a French drain is to use the wrong type of filtration fabric—or no fabric at all. 

The wrong fabric may not allow water to drain into the perforated pipe. Or, it may allow too much water and sediment to enter the trench and the perforated pipe, resulting in clogs.

Not using filtration fabric in a French drain is a major mistake because sediment will rapidly clog the drain.

Drainage fabric acts as a separator between the soil and the drainage filler material.

Line the French drain trench with non-woven drainage fabric explicitly designed for drains. This type of fabric provides the correct porosity and drainage flow rate.

Avoid using woven landscape fabric for French drains. Landscape fabric is intended for weed control and should not be used with French drains.

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Using Solid Pipe

Using solid pipe in the French drain trench is a common mistake. This mistake is easy to make since solid corrugated pipe looks like perforated corrugated pipe at first glance.

Solid pipe will not allow water to pass through the French drain. Water may continue to pass through the fill material alone, but at a slower rate than if perforated pipe were also carrying water.

Use 4- or 6-inch diameter perforated corrugated (ridged) drain pipe. Examine the pipe carefully for the perforations, which appear as short slits. 

Wrong Fill Material

Using the wrong type of rock as a fill material in a French drain is a mistake because it may not allow the water to reach the perforated pipe at the correct rate. Or it may entirely prevent water from percolating downward.

Pea gravel and crushed gravel are types of stone commonly used in error when installing a French drain:

• Pea gravel: Pea gravel stones are so small that they pack densely together, reducing water flow. Pea gravel is best used for patios or walkways.
• Crushed gravel: Crushed gravel contains fine dust that can clog French drains. Crushed gravel works well for driveways or as a base material for concrete paver, stone, or brick walkways.

Use 1-1/2-inch round drain rock as the aggregate fill material in a French drain. The larger stones avoid packing together. The rounded texture ensures that there will always be spaces between the stones.

Poor Slope Angle

French drains are sometimes mistakenly sloped at a low angle or no angle at all (that is, flat).

Since the purpose of a French drain is to remove accumulated water from the yard, it cannot move the water if it is not adequately sloped downward. 

The French drain’s trench should be sloped downward from 0.5-percent to 1-percent. The slope should be pointing in a direction away from the house and other protected areas.

A 1-percent slope means that it drops 1 foot vertically for every 100 horizontal feet.

No Discharge Station

A French drain with no discharge station will create pools of water, possibly flooding other parts of the yard or flowing back to the house or on adjacent properties.

Without a discharge station, the drain may also back up within the pipe and stop flowing altogether.

Identify a good discharge station for the French drain: a drainage ditch, swale, or dry well. Or you can discharge the French drain onto the side of a slope. 

You may be able to discharge the French drain to a city or other public storm drain. Check with your municipality before doing so.

Routing Downspout to the Drain

Water from the roof is routed downward—first sideways along the gutters, and then downward via the downspouts. 

Routing roof water directly into a French drain is a mistake because the sudden influx of water may overwhelm the French drain. 

The best way to manage downspout water is to send it into catch basins at the end of each downspout. 

The catch basins must be attached to solid (not perforated) PVC, ABS, or corrugated pipe. The pipes should end at pop-up drains far from the house and the French drain, or into a drainage ditch.

Placing Heavy Items on the Drain

Frequently driving or parking vehicles on French drains may crush the perforated pipe and compact the fill material. Placing extremely heavy items like buildings on French drains may also impact the pipe and filler. 

It’s fine to occasionally drive over a properly installed French drain that’s 18 inches deep or lower. But try to avoid frequently driving over the drain or parking on it. 

Avoid siting buildings over French drains. Not only may this impact the pipe and filler but it also reduces the drainage area.