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

A French drain is an essential part of a yard drainage system. It helps remove standing water from the yard and house foundation by giving water a path of least resistance.

Though a French drain mainly consists of three elements—perforated pipe, filtration fabric, and gravel—it's easy to make costly and time-consuming mistakes when installing one.

Learn about the common mistakes DIYers make when installing a French drain and how to avoid them.

Wrong Filtration Fabric

A common mistake when installing a French drain is using the wrong type of filtration fabric—or not using fabric at all.

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

Not using filtration fabric is a major mistake because sediment will quickly clog the drain.

Filtration fabric separates the soil from the drainage filler material.

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

Don't use woven landscape fabric for French drains. Landscape fabric is meant for weed control and isn't suitable for French drains.

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Using Solid Pipe

Using solid pipe in the French drain trench is another common mistake. This mistake is easy to make because solid corrugated pipe looks similar to perforated corrugated pipe at first glance.

Solid pipe won't allow water to pass through the French drain effectively. Water may still pass through the fill material, but at a slower rate than if perforated pipe were also carrying water.

Use 4- or 6-inch diameter perforated corrugated (ridged) drain pipe. Make sure to check for the perforations, which look like small slits.

Wrong Fill Material

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

Two common types of stone mistakenly used in French drains are:

• Pea gravel: Pea gravel stones are so small that they pack tightly together, reducing water flow. Pea gravel is best 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 pavers, 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 tightly together, and the rounded texture ensures there are always spaces between the stones.

Poor Slope Angle

French drains sometimes get installed with a low slope angle or no angle at all (flat).

The purpose of a French drain is to remove accumulated water from the yard, and it can't do that effectively if it's not adequately sloped downward.

The French drain trench should have a slope of 0.5 to 1 percent, directing water away from the house and other protected areas.

A 1-percent slope means a 1-foot vertical drop for every 100 horizontal feet.

Example

A 50-foot French drain that starts at a depth of 18 inches should be 24 inches deep at the end of its run.

No Discharge Station

A French drain without a discharge station will cause water to pool, potentially flooding other parts of the yard or flowing back to the house or neighboring properties.

Without a discharge station, the drain can 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 also be able to discharge the French drain into a city or public storm drain. Check with your local municipality before doing so.

Routing Downspout to the Drain

Water from the roof moves first along the gutters and then down through the downspouts.

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

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

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

Placing Heavy Items on the Drain

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

It's okay to occasionally drive over a properly installed French drain that's 18 inches deep or deeper. But try to avoid frequently driving over it or parking on it.

Avoid building structures over French drains. Not only can this impact the pipe and filler, but it also reduces the drainage area.

FAQ

How deep should a French drain be buried?

A French drain should be buried 18 inches below ground level. It should start at 18 inches and slope downward at a 1-percent or greater angle.

What should be at the end of a French drain?

The French drain should end at a discharge station. This can be a ditch, dry well, slope, or public storm drain (if allowed).

Should you cover a French drain with dirt?

No, you should not cover a French drain with dirt. Covering it with dirt will clog the fill material and impede water flow.