Project recipe
Install a French Drain
A French drain without fall is a buried trench full of water. This checks your slope first, then sizes every material from your actual run — gravel in tons, pipe, fabric, and the spoil you'll need to get rid of.
- A slope check against the 1% minimum, before you dig
- Gravel in tons, pipe, fabric and fittings for your run
- Cubic yards of spoil to remove — the forgotten line item
- Material cost against an installed price range
- The build sequence, with the outlet decision up front
- A clear boundary on what isn't a DIY job
Install a French Drain — interactive tool
The run
Total drop from the high end to the outlet.
If yes, this stops being a yard-drainage project.
Catch basins and prices
One at the low point of each area you're draining.
60 ft · 18 in deep · clay soil
Your French drain materials
of clean angular drainage gravel
- Pipe
- 63 ft
- Filter fabric
- 276 sq ft
- Spoil to remove
- 4.16 cu yd
- Fall available
- 12 in
- Fall needed
- 7.2 in
- Two people
- ~3.4 days
Slope check: 1.67% fall — that works. You have 12 in of drop over 60 ft, against the 7.2 in minimum.
Home & Garden Living · homeandgarden.living/projects/french-drain
Call 811 before you dig — this one is not optional
You're opening a 18 in trench over 60 ft. That is deep enough and long enough to reach gas, electric, water, sewer and communications. Utility locating is free, legally required in most of the US, and takes several days. Book it before anything else.
Clean angular gravel, and pipe holes down
Two details decide whether this works in ten years. Use washed, angular ¾ in stone, never pea gravel — rounded stone packs tight and stops draining. And lay perforated pipe with the holes facing down: water rises into the pipe from below, and holes-up lets silt in from above.
Clay makes this slower but more worthwhile
Clay is why you have the problem and also why the digging is hard. Wrap the trench fully in filter fabric — clay fines are exactly what silts a drain up — and expect the excavation to take about a day longer than the same run in loam.
| Item | Quantity | Cost |
|---|---|---|
| Washed drainage gravel (¾ in clean, angular)Clean and angular — not pea gravel, which packs and stops draining | 3.87 tons | $178 |
| 4 in perforated corrugated pipe with sockHoles down, not up — the water enters from below | 63 ft | $120 |
| Non-woven geotextile filter fabricWraps the whole trench — this is what stops it silting up | 276 sq ft | $88 |
| Couplers and fittings | 2 | $18 |
| Catch basin with grateSited at the lowest point of each area you're draining | 1 | $42 |
| Outlet grate and solid discharge pipeSolid pipe for the last run — perforated pipe at the outlet just re-wets the ground | 10 ft | $48 |
| Trench spade, tamper and wheelbarrow hire | 2 days | $95 |
| Materials total (DIY) | $589 | |
- Installed
- $1,500–$3,600
- You'd save
- $1,961
- Trench volume
- 3.33 cu yd
- Catch basins
- 1
The build, in order
- Call 811
2–5 days ahead
Free utility locating. Everything else waits on this.
- Confirm the outlet
1 hour
Know where the water goes before the first spade. Downhill, on your own land, legally.
- String the fall
1 hour
Set line at 7.2 in of drop minimum over 60 ft, and check it as you dig.
- Excavate
2 day(s)
18 in deep, 12 in wide. Clay is roughly a day slower than loam.
- Line with fabric
2 hours
Bottom and both sides, with enough excess to fold over the top.
- Bed, pipe, backfill
Half a day
2 in of gravel, pipe holes DOWN, then gravel to within 2 in of the surface.
- Fold, cover, test
2 hours
Fold the fabric over, cover, then run a hose at the top end and watch it come out the bottom.
Your shopping list
$589Trench
Pipe
Outlet
Tools
Take these numbers further
What this estimate assumes
- · 1% is treated as the minimum usable fall — 1 inch of drop for every 8 feet of run. Below that, a French drain becomes a buried trench that holds water.
- · Gravel is calculated to fill the trench less the pipe volume and the top 2 inches, at 1.4 tons per cubic yard.
- · Spoil is 1.25× the trench volume, because excavated soil swells.
- · Filter fabric covers the trench bottom, both sides and a top overlap, plus 15% for laps.
- · Installed pricing is $25–60 per linear foot, a 2026 US range for yard drainage. Foundation drainage costs considerably more.
- · Scope is surface and yard drainage only. Foundation drains, footing drains and slope seepage are structural work and are routed to a professional.
- · Prices are editable defaults. Replace them with your supplier's numbers.
Surface and yard drainage only. Foundation work, footing drains and slope seepage are structural — this tool routes those to a professional rather than instructing them.
A French drain is a simple thing: a trench, a filter fabric, a perforated pipe, and gravel. Water in the soil moves into the gravel, into the pipe through the holes, and downhill to somewhere useful. There is almost nothing to it.
Which is exactly why so many fail. The two decisions that determine whether it works are made before the first spade goes in, and neither is about materials. The first is slope: without at least 1% of fall — one inch of drop for every eight feet of run — water enters the pipe and stays there, and you have buried an expensive trench. The second is the outlet: a French drain moves water, it does not make it disappear, and "downhill towards the neighbour's fence" is a legal problem in most jurisdictions and a neighbour problem in all of them.
So this tool checks the slope before it gives you a materials list, and asks where the water goes before it gives you a sequence. Then it sizes everything from your actual run — gravel in tons because that is how it's sold, fabric with the laps included, and the cubic yards of spoil, which is the line item that turns up as a surprise on excavation day.
One boundary, stated plainly: this covers surface and yard drainage. Foundation drains, footing drains, and water seeping out of a slope are structural and waterproofing work. They can undermine footings and they can route water toward a building rather than away from it. Those get specified by a drainage contractor or an engineer, and this page will tell you when you've described one.
Slope: the thing that decides everything
One percent is the practical minimum — one inch of fall for every eight feet of run. Over a 60 foot drain that is 7.5 inches of drop from the high end to the outlet. More is better; less does not work, and no amount of gravel compensates for it.
Measure it before you commit. Run a string line from the high end to where the outlet will be, level it with a line level, and measure down to the ground at the outlet end. That distance is your available fall. If it is less than the run demands, you have four options: shorten the run, deepen the outlet end (which means the trench gets deeper as it goes), re-route to somewhere lower, or use a pumped basin instead of a gravity drain.
Then hold the fall as you dig. It is much easier to keep a string line true than to discover a high spot in the middle after the gravel is in. Check it every ten feet.
Where does the water go?
Answer this before you buy anything. There are three legitimate outlets.
Daylight is the simplest: the pipe emerges at a lower point on your own property and discharges onto the surface. It needs somewhere genuinely lower and somewhere the water can go without becoming someone else's problem. Use solid rather than perforated pipe for the last few feet, or the water simply re-wets the ground before it gets there, and fit a grate to keep rodents out.
A dry well is a buried chamber that lets water soak away. It works where the soil below actually percolates, which in clay it usually doesn't. Test it: dig a hole, fill it with water, and see how fast the level drops. If it's still full an hour later, a dry well will be too.
A storm connection is the most reliable and the most regulated. Many municipalities require a permit to connect private drainage to a public storm system, and most prohibit connecting anything to a sanitary sewer outright. Ask before you dig.
- Discharging onto a neighbouring property is unlawful in most jurisdictions. Don't design around it.
- Use solid pipe for the final run to a daylight outlet, not perforated.
- Fit a grate or animal guard at any daylight outlet.
- Check where the water ends up in a genuine storm, not just in ordinary rain.
The two material details that decide the ten-year outcome
Use clean, angular, washed drainage stone — typically ¾ inch. Not pea gravel. Rounded stone packs tightly together and the void space between the particles, which is the entire point of the gravel, largely disappears. Angular stone locks together while keeping the voids open.
And lay the perforated pipe with the holes facing down. This surprises people every time, and it is correct: water rises into the pipe from the saturated gravel below. Holes up means water has to fill the trench to pipe height before it can enter, and it lets silt fall in from above.
Wrap the whole trench in non-woven geotextile — bottom, both sides, and folded over the top. Silt migrating into the gravel is what kills a French drain over five to ten years, and the fabric is what stops it. It's the cheapest material in the trench and the one most often skipped.
What it costs, and what a contractor charges
Installed yard drainage runs roughly $25–60 per linear foot across most of the US, varying with depth, access, soil, and how far the spoil has to travel. A 60 foot run is therefore somewhere between $1,500 and $3,600 installed.
Materials for the same run typically come to $400–800. The gap is labour, and the labour is the honest reason to consider hiring it: a 60 foot trench at 18 inches deep in clay is around 3 cubic yards of excavation and about 4 tons of gravel, all of it moved by hand unless you rent a mini excavator. Two people, two days, and the second day is worse than the first.
Where a contractor genuinely earns the difference is on the parts that aren't digging: reading the site correctly, confirming the outlet is legal, and getting the fall right over a long run. If your run is short, the fall is obvious, and the outlet is clear, this is a very achievable DIY project. If any of those three is uncertain, pay for the assessment even if you do the digging.
Step by step
The order matters more than the technique. Skipping ahead is what causes rework.
Call 811 and wait
Request utility locating before anything else. It is free, legally required in most of the US, and takes several days — so it decides your schedule. You're opening a trench deep enough and long enough to reach gas, electric, water, sewer and communications lines. Book the gravel delivery and any equipment hire around the locate date, not before it.
Tip: Mark your intended route with paint or flags before you call. The locators mark what's underneath; you need to know whether their marks cross your line.
Confirm the outlet
Decide exactly where the water will discharge and confirm it is legal and genuinely lower. Daylight onto your own property, a dry well where the soil percolates, or a permitted storm connection. If you're considering a dry well, do a percolation test now: dig a hole, fill it, and time how fast it drains. In clay it usually won't.
Tip: Walk the route during heavy rain first if you can. Where water actually goes is frequently not where you assumed it went.
String the line and check the fall
Run a string from the high end to the outlet, level it, and measure down to the ground at each end. You need at least 1% fall — one inch of drop per eight feet of run. If you don't have it, stop and solve that before digging: shorten the run, deepen the outlet end, re-route lower, or plan a pumped basin instead.
Tip: Leave the string in place through the whole excavation and measure down from it every ten feet. Correcting the fall as you dig is trivial; correcting it afterwards means digging twice.
Excavate the trench
Dig to your planned depth — 18 to 24 inches is typical for yard drainage — and about 12 inches wide for a 4 inch pipe. Keep the fall consistent to the outlet. Barrow the spoil straight to where it's going rather than heaping it beside the trench, because it swells about 25% once dug and there is more of it than you expect.
Tip: In clay, dig on a dry day. Wet clay sticks to the spade, weighs enormously, and turns a hard day into a miserable one.
Line the trench with filter fabric
Lay non-woven geotextile along the bottom and up both sides, leaving enough excess at the top to fold over the finished gravel later. Overlap any joins by at least 12 inches. This is what stops silt migrating into the gravel and clogging the drain, and it's the cheapest material in the trench.
Tip: Hold the fabric to the trench walls with a few landscape staples so it doesn't collapse inward while you're shovelling gravel.
Bed, lay the pipe, and backfill with gravel
Put down about 2 inches of clean angular gravel, then lay the perforated pipe on top with the holes facing DOWN. Check the fall along the pipe with your string line. Then backfill with gravel to within about 2 inches of the surface, keeping the fabric flat against the trench walls as you go.
Tip: Use washed angular ¾ inch stone, never pea gravel. Rounded stone packs tight and the void space — the whole point of the gravel — disappears.
Fold, cover, and test before you finish
Fold the excess fabric over the top of the gravel, overlapping it, then cover with 2 inches of soil and turf, or leave the gravel exposed if it's a surface drain. Before you replace the turf, run a hose at the high end for several minutes and confirm water comes out at the outlet. Finding a problem now costs an hour; finding it next spring costs the whole trench.
Tip: Photograph the open trench with a tape measure in shot before you cover it. In three years, when you're planting or digging nearby, you'll want to know exactly where it runs and how deep.
What it costs
| Item | Typical cost |
|---|---|
| Clean angular drainage gravel (~4 tons for 60 ft) | $180–280 |
| 4 in perforated pipe with sock, 63 ft | $110–150 |
| Non-woven geotextile filter fabric | $60–120 |
| Couplers and fittings | $20–50 |
| Catch basin with grate (each) | $35–60 |
| Outlet grate and solid discharge pipe | $40–70 |
| Tool hire (trenching spade, barrow, tamper) | $60–120 |
| Spoil disposal, if you can't use it on site | $0–250 |
What this tool assumes
Every number this tool produces rests on these. Change your inputs and they change with you.
- 1% is treated as the minimum usable fall — 1 inch of drop for every 8 feet of run.
- Gravel fills the trench less the pipe volume and the top 2 inches, calculated at 1.4 tons per cubic yard.
- Spoil is 1.25× the trench volume, because excavated soil swells.
- Filter fabric covers the bottom, both sides and a top overlap, plus 15% for laps.
- Installed pricing of $25–60 per linear foot is a 2026 US range for yard drainage. Foundation drainage costs considerably more.
- Scope is surface and yard drainage only. Foundation drains, footing drains and slope seepage are routed to a professional.
Mistakes that cause rework
Each of these costs money or a whole weekend to undo.
Building it without enough fall
Below 1% the water enters the pipe and stays there. This is the single most common French drain failure and it's fully avoidable — measure the fall with a string line before you dig, not after.
Pea gravel instead of clean angular stone
Rounded stone packs tight and loses the void space that makes the trench work. Ask specifically for washed angular ¾ inch drainage stone.
Laying the pipe holes up
Water rises into the pipe from the saturated gravel below. Holes up means the trench has to fill to pipe height before anything drains, and silt falls in from above.
Skipping the filter fabric
It's the cheapest material in the trench and it's what stops silt clogging the gravel. A drain without it typically works for five years and then quietly stops.
Not deciding the outlet first
A French drain moves water; it doesn't remove it. Discharging onto a neighbouring property is unlawful in most jurisdictions, and discovering that after the trench is dug is an expensive lesson.
Forgetting where the spoil goes
A 60 ft trench at 18 in deep produces around 3.5 cubic yards of soil, and it swells as you dig it. Arrange for it before excavation day.
Safety & honest limits
- Call 811 before you dig. This is not advisory — striking a gas or electrical line is life-threatening, and utility locating is free and legally required in most of the US.
- Foundation drains, footing drains and any excavation within a few feet of a structure are out of scope here. They can undermine footings and route water toward the building. Get those specified by a drainage contractor or structural engineer.
- Water seeping from partway down a slope can indicate a perched water table or, occasionally, slope instability. Have it assessed on site before digging into the hillside.
- Never enter a trench deeper than about 4 ft without proper shoring. Trench collapse is a leading cause of excavation fatalities, and soil is far heavier than people intuit.
- Discharging drainage onto a neighbouring property is unlawful in most jurisdictions. Confirm your outlet is legal before you build.
- Many municipalities require a permit to connect private drainage to a public storm system, and prohibit connecting to sanitary sewer entirely.
- Costs are estimates, not quotes.
Frequently asked questions
How much slope does a French drain need?
At least 1% — one inch of fall for every eight feet of run. Over a 60 foot drain that's 7.5 inches from the high end to the outlet. Below that, water enters the pipe and stays there, and no amount of gravel compensates.
How deep should a French drain be?
18 to 24 inches is typical for yard drainage — deep enough to intercept water moving through the topsoil and to hold a useful volume of gravel. Deeper isn't automatically better; what matters far more is consistent fall to the outlet.
Should French drain pipe holes face up or down?
Down. Water rises into the pipe from the saturated gravel beneath it. Holes facing up means the trench has to fill to pipe height before anything drains, and silt falls in from above. This is the detail people get wrong most often.
What gravel do you use for a French drain?
Clean, washed, angular drainage stone, typically ¾ inch. Never pea gravel — rounded stone packs tightly and loses the void space between particles, which is the entire mechanism the trench relies on.
How much does a French drain cost?
Installed, roughly $25–60 per linear foot in the US, so $1,500–3,600 for a 60 foot run. Materials for the same run are typically $400–800. The gap is labour, and the labour is genuinely hard — about 3 cubic yards of excavation and 4 tons of gravel moved by hand.
Do I need filter fabric in a French drain?
Yes. Silt migrating into the gravel is what clogs a French drain over five to ten years, and non-woven geotextile wrapped around the whole trench is what prevents it. It's the cheapest material in the trench and the most commonly skipped.
Where should a French drain discharge?
Somewhere genuinely lower on your own property, into a dry well where the soil percolates, or into a permitted storm connection. Not onto a neighbouring property — that's unlawful in most jurisdictions. Decide this before you dig, because it determines the whole route.
Can I install a French drain along my foundation myself?
We'd advise against treating that as a DIY project. Excavating against a foundation is structural and waterproofing work: it can undermine footings and, done wrong, can route water toward the building. This page covers surface and yard drainage; foundation drainage should be specified on site by a contractor or engineer.
Last reviewed July 25, 2026 · Home & Garden Living
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