Water that pools against your foundation, floods a low spot in the yard, or seeps into the basement is not a problem that fixes itself. Learning how to install a french drain gives you a proven, gravity-powered way to redirect that water away from where it does damage. A French drain is deceptively simple, a gravel-filled trench with a perforated pipe that carries water downhill, but the details of slope, depth, and materials separate a drain that works for decades from one that clogs in a season. This guide walks you through the whole process.
How a French Drain Works
The concept is elegant. Water always follows the path of least resistance and flows downhill. A French drain provides that easy path: a trench filled with washed gravel around a perforated pipe. Surface and subsurface water seeps into the gravel, drops into the pipe through its holes, and the pipe carries it by gravity to a lower discharge point, a dry well, a storm drain, a daylight outlet on a slope, or the street. There are no pumps and no moving parts, which is why a properly built French drain is so reliable.
Plan Before You Dig
Good planning prevents the two most common failures: a drain that runs uphill and a drain that has nowhere to send its water. Start here:
- Identify the water source and the destination. The outlet must be lower than the start so gravity can do its job.
- Confirm the slope. Plan for at least a 1 percent grade, about 1 inch of drop for every 8 to 10 feet of run.
- Call 811 first. Have underground utilities located before you put a shovel in the ground. This is free and non-negotiable.
- Check local codes for where you are allowed to discharge water, since dumping onto a neighbor’s property is often prohibited.
Mark the trench line with spray paint or a garden hose, following the natural downhill path from problem area to outlet.
Gather Your Materials and Tools
For a typical residential French drain you will need:
- Perforated drain pipe, usually 4-inch corrugated or rigid PVC with holes.
- Washed drainage gravel (3/4-inch clean stone), which resists clogging better than fine gravel.
- Landscape filter fabric to line the trench and keep soil from migrating into the gravel.
- A shovel or trenching shovel, and a rental trencher for long runs.
- A wheelbarrow, level, tape measure, and utility knife.
Buy more gravel than you think you need; trenches always swallow more stone than the calculation suggests.
Step-by-Step Installation
With planning done and materials on hand, here is the process:
- Dig the trench. Aim for 8 to 12 inches wide and 18 to 24 inches deep, deeper if you are addressing a foundation. As you dig, maintain that consistent downhill slope. Check it frequently with a level on a long board.
- Verify the grade. Lay a board in the trench with a level on top and confirm continuous fall toward the outlet. Any flat or reverse section will trap water and cause failure.
- Line the trench with filter fabric. Drape it so there is enough excess on both sides to wrap over the top of the gravel later. This fabric is what keeps silt out and the drain flowing for the long haul.
- Add a base layer of gravel. Spread 2 to 3 inches of washed stone along the bottom to cradle the pipe.
- Lay the perforated pipe. Place it on the gravel with the holes facing down, which lets water enter from the water table and move along efficiently. Keep the slope consistent.
- Cover the pipe with gravel. Backfill with washed stone until the pipe is surrounded and covered by several inches, leaving a few inches below finished grade.
- Wrap the fabric over the top. Fold the excess filter fabric over the gravel like a burrito to seal out soil from above.
- Cap the trench. Top with a few inches of soil and sod, or leave a decorative gravel surface if you want a visible drain that also captures surface water.
Pipe Orientation and the Great Debate
Homeowners often ask whether the pipe holes should face up or down. For a subsurface drain lowering the water table, holes facing down is the traditional and generally recommended orientation, so water can enter from below and the pipe fills from the bottom up. If your primary goal is capturing surface water quickly, some installers point the holes up. For most foundation and yard-drainage projects, holes down performs well. What matters far more than this detail is a clean gravel envelope, filter fabric, and consistent slope.
Where to Send the Water
Your drain is only as good as its outlet. Options include daylighting the pipe on a downhill slope where water can safely exit, running it to a dry well (a gravel-filled pit that lets water percolate into the soil), or connecting to a storm drain where local code permits. Never discharge toward the foundation, a neighbor’s yard, or a spot that will simply create a new soggy area. Install a rodent guard or grate on any open outlet.
How Much Time and Money to Budget
A DIY French drain is labor-intensive but affordable in materials. For a typical 50-foot residential run, expect to spend roughly $200 to $600 on gravel, pipe, and fabric, with the gravel being the biggest line item since a trench swallows a surprising amount of stone. Renting a trencher for a day, often $100 to $200, saves your back on longer runs, though a short drain can be dug by hand.
Time-wise, plan a full weekend for a moderate run if you are digging by hand: a day to dig and grade, and a day to lay fabric, gravel, pipe, and backfill. Hiring a pro to install a French drain generally runs $25 to $60 per linear foot depending on depth, soil, and access, so that same 50-foot drain might cost $1,250 to $3,000 installed. The DIY savings are real, but so is the effort, be honest about whether you have the time and stamina for the digging.
Maintaining Your French Drain
A well-built French drain is close to maintenance-free, but a little attention keeps it flowing for decades. Check the outlet a few times a year and clear any debris, leaves, or sediment blocking the discharge point, and make sure the rodent guard or grate is intact. After heavy storms, confirm water is actually exiting at the outlet rather than backing up, which would signal a clog or a lost slope.
If flow slows over the years, the usual culprit is silt that has worked into the gravel, which is exactly what the filter fabric is there to prevent, another reason not to skip it. For drains with a cleanout riser, you can flush the pipe with a hose or a sewer jetter to clear buildup. Keep the surface above the drain free of heavy compaction and avoid planting deep-rooted shrubs directly over the line, since roots seek out the moisture and can eventually invade the pipe. With these simple checks, your drain will keep protecting your foundation year after year.
Avoiding Common Mistakes
Another frequent misstep is undersizing the system for the water volume. If you are draining a large area or a chronic wet zone, a single 4-inch pipe in a narrow trench may not keep up during heavy storms, leaving you to redig later, so when in doubt go wider and deeper. Forgetting a cleanout is another; adding a capped vertical riser at the head of the run lets you flush the pipe years later without excavation. Beyond those, a few errors cause most failed French drains: skipping the filter fabric so silt clogs the gravel, using fine or dirty gravel instead of washed clean stone, and losing the slope somewhere along the run. Take your time getting the grade right, use quality washed stone, and always wrap the gravel in fabric. Do those three things and your French drain will quietly move water away from your home for 20 years or more, keeping your foundation dry and your yard usable.
