A properly installed French drain can be a game-changer for homeowners dealing with excess water, foundation issues or soggy yards. When done right, it redirects water away from your property, preventing erosion and long-term damage. But here’s the catch—French drains aren’t as simple as digging a trench and tossing in some gravel. Small mistakes during installation can lead to major headaches, costly repairs or even complete system failure.
We’ve seen it all—poor drainage design, the wrong materials and short-term solutions that don’t hold up over time. To save you from frustration (and wasted money), we’re breaking down some of the most common French drain mistakes. If you’re planning to install one yourself or you’re troubleshooting an existing system, here’s what you need to avoid.
Reusing Excavated Soil in the Trench
It might seem logical to put the soil you just dug up right back into the trench after installing the drain, but that’s one of the quickest ways to ruin the system. The whole point of a French drain is to improve drainage, and if the original soil wasn’t draining well before, it’s not going to start now.
Clay-heavy or compacted soil traps water, which can cause the trench to clog over time. Instead of refilling with the excavated dirt, use clean drainage stone to keep the water flowing freely. If you’re left wondering what to do with all that extra soil, consider repurposing it elsewhere in your yard or hauling it away.
Choosing the Wrong Drainage Fabric
Not all landscape fabrics are created equal and using the wrong type can seriously impact how well your French drain works. Many homeowners assume that any fabric will do, but woven geotextile fabric—the kind often used for weed barriers—can actually block water from passing through.
For a French drain, non-woven geotextile fabric is the way to go. It allows water to flow through while keeping soil and debris out of the drain rock. A 4-6 oz non-woven fabric is the best choice for long-lasting performance.
Installing a Gravel-Only Drain Without a Pipe
Some people think they can get away with just filling a trench with gravel and calling it a day. While gravel does help with water movement, a drain without a perforated pipe is far less effective—especially in areas with heavy rainfall or poor soil drainage.
The pipe is what truly directs water away from your property. A properly installed French drain should include a 4” or 6” perforated pipe surrounded by drainage rock. If you skip the pipe, water can pool in the trench, leading to backups and standing water issues.
Failing to Line the Trench with Drainage Fabric
A correctly installed French drain uses the “burrito wrap” method—where the entire drain system is enclosed in non-woven geotextile fabric. Skipping this step allows soil to mix with the drain rock, which eventually leads to clogs.
Without a fabric barrier, silt and fine particles from the surrounding soil will seep into the gravel over time, reducing the drain’s effectiveness. The goal is to keep everything separate so that water can move freely through the system without obstruction.
Not Checking for Underground Utilities Before Digging
Digging a trench without checking for underground utilities is not just a bad idea—it’s dangerous. Hitting a buried gas, water or electrical line can lead to costly repairs or serious safety hazards.
Before breaking ground, always call 811 to have utility lines marked. This simple step can prevent major issues and keep your project on track. Also, be sure to check with your local municipality or HOA for any restrictions on drainage placement.
Using the Wrong Type of Drain Rock
Not all gravel is suitable for a French drain. Some homeowners make the mistake of using crushed rock with fines, which can compact over time and restrict water flow. Others opt for pea gravel, which is too small and doesn’t allow for proper drainage.
The best choice is a washed round stone—such as 1.5” clean gravel—that allows water to flow freely through the system. If crushed stone is the only option available in your area, consider using a sock-wrapped perforated pipe to prevent clogging.
Directly Connecting a Downspout to the French Drain
It might seem convenient to tie your roof downspouts directly into your French drain, but doing so can overwhelm the system. During heavy rain, the volume of water coming from the roof can exceed what the drain is designed to handle, leading to backups and potential flooding.
A better solution is to install a separate drainage system for roof runoff. If you must connect the two, use a catch basin to help filter out debris before it enters the drain.
Ignoring Proper Slope for Drainage
A French drain works best with a gradual slope that allows water to flow away from your property. If the trench is too flat or contains low spots, water can pool instead of draining properly.
Aim for a minimum slope of 1% to ensure effective drainage—meaning the pipe should drop at least 1 inch for every 10 feet of length. Even a slight miscalculation here can lead to standing water and system failure.
Not Working With a Professional
Many homeowners take on French drain installation as a DIY project, only to realize too late that small mistakes can lead to big problems. From selecting the right materials to ensuring proper slope and placement, there’s a lot that can go wrong.
Professional drainage contractors understand how to design a system that lasts. They know which materials work best for different soil types, how to prevent clogging and how to ensure the water flows where it should. A well-installed French drain isn’t just about digging a trench—it’s about long-term effectiveness.
We specialize in designing and installing drainage systems that work. Whether dealing with a failing French drain or planning a new installation, our team has the expertise to do the job right. Don’t let simple mistakes cost you time and money—reach out to us today to schedule a consultation.