I've already written about what a French drain is, how it physically works, and the general installation process. This article is different on purpose: it's the project plan I'd actually hand someone who has decided, for real, to build one themselves this weekend — how much material to buy, what to rent, a realistic day-by-day schedule, and what to do if you test it and something's wrong. If you haven't decided yet whether this is a DIY job for your situation, read how to install a French drain first for the fuller picture, including exactly when I'd hire a licensed contractor instead. This one assumes you're building.
Confirm You're a Good DIY Candidate First
A weekend build is realistic for a straightforward exterior yard drain on flat-to-moderate ground, solving a surface-water or minor-seepage problem. It stops being a reasonable DIY project if you're fighting a high water table (standing water in the trench as you dig), the route needs to tie into a municipal storm system, or you're seeing any sign of actual foundation movement rather than a wet yard. If any of that describes your situation, compare licensed French drain installers near you instead of pushing ahead solo.
Step 1: Measure and Plan Before You Buy Anything
Walk the yard during or right after a hard rain and mark exactly where water sits or flows — not where you assume it does. Measure the total distance from that problem area to a safe discharge point (daylighting at least 10 feet from the foundation, a dry well, or an existing sump pit), and measure the elevation drop over that distance with a line level or a laser level. You need a minimum of about 1/8 inch of fall per foot of run; for a 40-foot run, that's a minimum of 5 inches of total drop from start to finish. If your yard doesn't have that much natural fall, you'll need to dig the starting end deeper to create it artificially.
Calculating How Much You Actually Need
This is the step people skip and then make two trips to the hardware store. For a trench roughly 12 inches wide and 20 inches deep:
- Pipe: Buy your total run length plus about 10% for waste and connections. A 40-foot run needs roughly 44 feet of 4-inch perforated pipe.
- Gravel: A rough rule of thumb is about 0.6 to 0.7 cubic yards of drainage gravel per 10 feet of trench at that depth and width, though this varies with your exact dimensions — most gravel suppliers can calculate an exact volume if you give them the trench length, width, and depth.
- Fabric: Buy enough non-woven landscape fabric to line the full width and depth of the trench with overlap at the top, plus about 15% extra for overlap at seams if you're joining rolls on a long run.
- Couplings and fittings: One coupling per joint, plus an end cap or pop-up emitter for the discharge point.
Order gravel delivery for a day or two after your planned dig, not the same day — trenches rarely go exactly as fast as planned, and a pile of gravel sitting in your driveway for a week is its own headache.
What to Rent vs. Buy
- For a short run (under ~30 feet) on soft soil: a flat spade and a trenching shovel are enough. Buy these; you'll use them again.
- For a longer run, or compact/rocky soil: rent a walk-behind mini trencher for the day. It dramatically cuts the physical labor and keeps your trench width more consistent, which helps with the gravel calculation above.
- Either way: rent or buy a line level or laser level. This is the one tool I wouldn't skip regardless of trench length, since slope is the detail that actually determines whether the whole project works.
A Realistic Day-by-Day Schedule
Several days before you dig: Call 811 (the national call-before-you-dig number) and wait for utility lines to be marked. This step has a mandatory waiting period in most states, so it has to happen before anything else, including ordering your rental equipment for a specific date.
Day 1 (half day): Order and pick up materials once utilities are marked. Mark your trench route with marking paint or stakes, confirming it avoids the flagged utility lines.
Day 1 or 2 (full day): Dig the trench, checking your slope every few feet as you go rather than only at the start and end. This is the single most physically demanding part of the project; a rented trencher on a 40-foot run can realistically compress this from most of a day down to a couple of hours.
Day 2 (half day): Line the trench with fabric, add the gravel base, lay and connect the pipe sections, add the covering gravel, and fold the fabric closed over the top.
Day 2 or 3 (half day): Backfill in layers rather than all at once, cap the surface with topsoil, sod, or stone, and confirm the discharge point is clear and correctly placed.
Same day: Test it. Don't wait for the next real storm to find out if it works.
I go through the technical detail of each of these steps — fabric type, which way the perforations should face, and the reasoning behind the 1/8-inch slope rule — in more depth in how to install a French drain and how a French drain actually works.
Testing It Before You Call It Done
Run a garden hose at the highest point of the drain for several minutes and physically walk the entire route, watching for pooling, slow movement, or water backing up anywhere along the trench, and confirm it exits cleanly at the discharge point. This is the only real way to catch a slope mistake before the next storm does it for you at a much less convenient time.
Troubleshooting: What to Do If the Test Fails
- Water pools at one spot along the route: that section likely has a low spot or reverse slope. If it's shallow, you may be able to re-excavate just that section and correct the grade without redoing the whole run.
- Water moves but very slowly: check whether your gravel has fine dust mixed in rather than being clean, washed stone — dusty gravel drains meaningfully worse than clean gravel from day one.
- No water reaches the discharge point at all: confirm the pipe wasn't accidentally crimped or disconnected at a coupling during backfill, and confirm the discharge end isn't blocked or buried.
- Water resurfaces right next to the discharge point: the discharge isn't far enough from the foundation, or the ground at that point doesn't have enough slope of its own to carry the water further away.
Once it's been running successfully for a season or two, an annual check-and-flush keeps it working long-term — I cover that maintenance routine, along with the signs a drain is starting to clog, in how to clean a French drain.
What This Actually Saves You
Professionally installed, a comparable exterior French drain typically runs $2,000 to $6,500. Building it yourself mostly saves the labor cost, since materials — pipe, fabric, and gravel — are commodity items; homeowners commonly budget somewhere around $5 to $15 per linear foot for materials alone, before counting rental equipment or your own time. Whether that trade-off is worth it depends entirely on how comfortable you are with the physical work and how confident you are catching your own mistakes before they're buried under two feet of dirt.
A Few Practical Things I'd Tell a First-Timer
- Don't dig the day before a forecasted heavy rain. An open trench that fills with water mid-project is miserable to work in and can undo your grading before you've even laid the pipe.
- Photograph the trench before you backfill. Once it's covered, you have no record of exactly where the pipe runs — a few phone photos with something for scale save real guesswork years later if you ever need to find it again.
- Plan where the excavated soil goes before you start digging. A 40-foot trench produces more displaced soil than most people expect, and having nowhere to put it mid-project slows everything down.
- Work with a helper if you can. One person checking slope with a level while the other digs catches mistakes in real time, instead of after the whole trench is already open.
Conclusion
Building your own French drain is a genuinely achievable weekend project if you respect the two things that actually determine success: getting the slope right the entire length of the run, and using real drainage gravel and filter fabric rather than whatever's cheapest. Measure and calculate your materials before you buy anything, rent a trencher if the run is long or the soil is difficult, and test it with a hose before you consider the job finished. If partway through planning you realize your situation involves a high water table, a storm-system tie-in, or any sign of foundation movement, that's the signal to stop and get a free estimate from a licensed contractor instead of pushing further on your own.