We’ve installed a lot of French drains here in Kansas City, and we’ve also had to repair a lot of bad ones. Sometimes it’s a DIY job that didn’t go as planned. Other times, it’s a contractor who cut corners. Either way, the result is the same: standing water, soggy yards, and frustrated homeowners.
So we figured we’d do everyone a favor and share the top French drain mistakes we see all the time, and how to avoid them. This isn’t theory, though, we’re out in the dirt fixing this stuff. Here’s what we’ve learned, what we do differently, and how you can get it right the first time.
1) Not Calling 811 Before Digging
Before you even grab a shovel, do yourself a favor and call 811. We’ve seen people hit gas lines and fiber optic cables because they skipped this step. It’s free, it’s easy, and in Missouri and Kansas, it’s also the law.
We always call a few days before starting any job, and when we’re digging near flags or paint, we switch to hand tools. Better safe than sorry.
2) Incorrect Slope
French drains only work if gravity’s doing the heavy lifting. We’ve fixed drains that just sat full of water because the slope was wrong—or worse, water was flowing backwards.
Here’s a rule of thumb: aim for about 1 inch of drop every 8–10 feet, which is 1%. On job sites, we use a laser level to check this as we dig, and you can use a simple level with a stick if you’re doing it by hand. Don’t eyeball it… water doesn’t lie.
3) Using Cheap Pipe
We get it! Corrugated pipe is much cheaper from your local box store. But it’s also gets squished and collapses easily. Dirt gets trapped in the ridges, roots sneak in, and good luck trying to clean it out after that.
For most of our installs, we use single wall perforated pipe from Prinsco. Occasionally, upon request, we will use French Drain Man’s 8 Slot pipe. These pipes are stronger, flow better, and don’t collapse when installed properly. You’ll spend a little more up front, but you won’t be calling someone like us to fix it in a year.
NOTE: In our Missouri soils, we much prefer HDPE pipe over PVC for many reasons. The first is that HDPE has a much higher “brittle” temperature (-220°F), over 200°F lower than that of PVC, meaning it won’t crack as temperatures plummet in the winter. The second is that Missouri and Kansas have clay-heavy soils which heave and move as temperatures change… and HDPE is much more flexible than PVC.
4) Skipping Filter Fabric (or Using the Wrong Kind)
Without fabric, your gravel turns into mud over time. We’ve dug up systems that were just clogged with silt because there was nothing to keep the dirt out. Some of these awful systems even use non-permeable weed filter fabric, which means water couldn’t even enter the system.
We always use non-woven geotextile fabric, preferably fabric that weighs 4oz. It lets water through but blocks dirt and roots. Wrap the trench like a burrito: fabric down first, then gravel and pipe, then fold it over the top before backfilling.
5) Too Little Gravel (Or None)
Some folks try to save money on gravel and don’t use it, or even just toss a few inches in. Don’t do that. Gravel is what actually helps the water flow into your pipe. The air pockets between the pieces of gravel are opportunities for water to fall into, which we call “void”. Without enough of it, your drain can’t breathe.
The French drain perforated pipe ALWAYS lays at the bottom of the trench, directly on the fabric. We try to aim for at least 6″ of gravel, but always stop 4-6″ before the top of the trench, which allows us to top it with soil, and seed it. The more gravel, the better the flow.
6) No Catch Basins Where They’re Needed
Catch basins aren’t for every system, but they’re game changers in areas where water puddles fast. We’ve added catch basins to systems that just couldn’t keep up, and installed them in the bottom of a swale for instant improvement.
We like placing 12″ basins in problem spots and tying them into the main line with solid pipe. NEVER tie a catch basin or downspout discharge line into a French drain line or you will be adding extra stress to the system.
7) Burying the Pipe Too Shallow
We’ve seen pipes buried so shallow they freeze in winter, such as the image above where the PVC pipe (which had a pipe sock around it) had about 2″ of dirt on top of it. Placement matters.
In most yards, 12–18 inches deep is the sweet spot. Deep enough to catch groundwater, but shallow enough to avoid the water table and keep everything working year-round. If you’re DIYing and want to get real nerdy, you can find the groundwater level data using the United States Geological Survey website’s National Water Dashboard.
8) Dumping Water Out in the Wrong Spot
This is one of the most frustrating mistakes to fix. We’ve seen systems that move water beautifully—only to dump it right back near the foundation or into the neighbor’s yard.
We always discharge at least 25 feet from the house, downhill from the collection points. Pop-up emitters are our client’s favorite because they are low maintenance, easy to install, and are discrete.
9) Letting Tree Roots Clog the System
Roots love French drains. It’s dark, it’s damp, and it’s an open invitation for trouble. We’ve pulled roots the size of baseball bats out of some systems.
Avoid planting trees or large shrubs near your system. If they’re already there, smooth pipe and filter fabric give you a fighting chance. We’ve also done reroutes for clients who lost the battle… sometimes it’s the only option.
10) Installing a French Drain When a Simpler Solution Would’ve Worked
Sometimes people jump straight to a French drain because it sounds like the ultimate fix, but that doesn’t mean it’s always the right first move. We’ve had clients call us after spending thousands on a DIY French drain, only to find out that just burying a gutter downspout or installing a strategically placed catch basin would’ve done the trick.
Here’s a good rule of thumb: always identify the source of the water before designing the solution. If water is pooling near a downspout, fix the downspout first. If the yard is flat and water just needs a place to go, a catch basin or some yard regrading might be all you need. French drains are great, but they’re overkill for simple runoff issues… and overkill often comes with extra cost, labor, and risk of installation errors.
So before you start digging trenches and laying pipe, step back. Ask yourself: “Is there a simpler way to reroute this water?” You might save yourself a weekend and a whole lot of cash.
11) Not Compacting Soil or Leaving a Slight Mound Over the Trench
Here’s something most DIYers don’t think about until it’s too late: your trench will settle. Every time. No matter how neatly you backfill it, the ground is going to sink as rain, gravity, and time do their thing. If you just fill the trench flush with the surrounding lawn and call it good, you’ll have a sunken path in your yard within 6–12 months: a French drain with a built-in trip hazard.
What we do on jobs is either compact the soil in layers as we go or leave a slight 2-inch mound over the trench, although usually both. That way, as everything settles naturally over time, it levels out instead of dipping below grade. Compacting helps, but even compacted soil settles, especially if you’re using a lot of gravel in the trench.
This is one of those simple, invisible finishing touches that separates a DIY job from a professional one. Your grass will grow better, your yard will stay level, and you won’t have to explain to guests why there’s a trench-shaped rut running through your backyard.
Final Thoughts: Learn From Us, or Hire Us
We’ve been called in to fix almost every mistake on this list. And while we’re happy to help, we’d much rather you get it right the first time. Whether you’re a handy homeowner or thinking of hiring it out, now you know what to look for.
If you’re in Kansas City and want it done right the first time (or need us to fix a system that didn’t work) reach out to us by booking a free consultation using the button at the top of this page. We’d be glad to help!