How to Add a Curtain Drain to a Soggy Slope (DIY Guide)

TL;DR: A curtain drain is a gravel-filled trench with perforated pipe that intercepts groundwater moving downhill before it reaches your house or a low spot in the yard. Dig it at least 18-24 inches deep, cross the slope perpendicular to water flow, and give the pipe a 1% slope (about 1 inch of drop per 8 feet) toward daylight or a dry well. Most DIY installs run 20-60 feet and cost $150-$400 in materials, versus $1,500-$4,000 for a contractor job.

_Last reviewed: July 2026 · 8 min read_

If your backyard turns into a sponge every time it rains, or water keeps finding its way toward your foundation from higher ground, a French drain along your house won't fix it. You need something farther upslope, catching the water before it ever reaches the problem area. A curtain drain does exactly that, and it's one of the more forgiving drainage projects a homeowner can tackle without hiring anyone.

Okoniq Property Hub lets you log the trench depth, pipe run, and outlet location once you're done, so the next time you're troubleshooting a wet spot you have the actual dimensions instead of a guess.

What exactly is a curtain drain and how is it different from a French drain?

A curtain drain intercepts water moving downhill across a slope; a French drain typically runs alongside a foundation to collect and redirect water that's already arrived. Both use the same materials — perforated pipe wrapped in fabric, buried in gravel — but the placement and purpose differ.

Think of a curtain drain as a fence built underground. It sits perpendicular to the direction water is flowing, usually somewhere between the high point of your yard and the structure you're protecting. Water hits the gravel trench, drops into the perforated pipe, and gets carried sideways to an outlet instead of continuing downhill into your basement or crawlspace. If you're already dealing with downspout water dumping in the wrong place, fix that first — a curtain drain works best on groundwater and slope runoff, not concentrated roof discharge.

Where should you actually dig the trench?

Dig the trench across the slope, upstream of the wet area, at the point where the ground naturally narrows the water's path. Walk your yard during or right after a rainstorm and watch where the water actually travels — it's rarely a straight line downhill.

Most residential curtain drains sit 10-20 feet upslope from the foundation or low spot, but the right distance depends on your lot. On a lot with a 20-30 foot slope between the high point and the house, placing the drain roughly a third of the way down the grade usually intercepts the bulk of the flow. If your basement floods every spring, this same water is often what's contributing to 6 downspout mistakes that send water into your basement — the curtain drain and the downspout extensions need to work together, not one instead of the other.

How deep and how wide does the trench need to be?

The trench should be 18-24 inches deep and 12-18 inches wide for most residential slopes. Shallower than that and the drain only catches surface water; deeper cuts into the frost line in colder climates and adds cost without much benefit.

Line the trench with landscape fabric before adding gravel — this keeps silt from clogging the perforations over time. Lay 3-4 inches of ¾-inch drain rock at the bottom, set 4-inch perforated PVC or corrugated pipe (perforations facing down, contrary to what feels intuitive — water enters from below and along the sides, and facing down keeps sediment from settling directly in the holes), then backfill with more gravel to within 4-6 inches of grade. Cap it with topsoil and sod or mulch.

| Detail | Standard Curtain Drain | Deep/Heavy-Flow Curtain Drain | |---|---|---| | Trench depth | 18-24 inches | 30-36 inches | | Pipe diameter | 4 inch | 6 inch | | Typical cost (DIY, 40 ft) | $150-$300 | $350-$500 | | Best for | Moderate slope, seasonal wet spots | Steep grade, year-round seepage, clay soil |

What slope and outlet do you need for the pipe to actually drain?

The pipe needs roughly a 1% slope, meaning 1 inch of drop for every 8 feet of run, and it needs somewhere to send the water. Without both, you've just built an underground bathtub.

Use a string level or a 4-foot level with a shim to check the fall as you lay pipe. The outlet can be daylight (the pipe simply exits at a lower point on the property and empties onto the surface, ideally 10+ feet from the foundation), a dry well, or a connection into an existing storm drain if local code allows it. Check with your municipality before tying into a public storm system — some jurisdictions require a permit for that connection specifically, even though the trench itself usually doesn't. If your soil holds water long enough that you're also seeing signs indoors, it's worth ruling out a slab leak under your floor before assuming it's all surface drainage — plumbing leaks and yard drainage can produce similar wet patches and it's easy to blame the wrong one.

How do you maintain a curtain drain once it's in the ground?

Check the outlet twice a year, ideally in early spring and late fall, to confirm water is actually exiting and nothing's clogged with silt or roots. A curtain drain with a blocked outlet is worse than no drain at all, because the trench fills and has nowhere to send the water except back up.

Walk the trench line after heavy rain the first year to confirm there's no pooling directly above it — that usually means the gravel settled or the fabric shifted. Keep an eye on nearby tree roots too; roots are drawn to the moisture and gravel and can work their way into the pipe within 5-8 years if a fast-growing species is planted too close.

FAQ

How much does it cost to install a curtain drain yourself?

A 40-foot curtain drain typically costs $150-$400 in materials — pipe, gravel, and fabric — versus $1,500-$4,000 if you hire a landscaping or drainage contractor to do the same run.

Can a curtain drain fix a wet basement on its own?

Usually not by itself. A curtain drain reduces the groundwater reaching your foundation, but if your downspouts, grading, or gutters are also contributing, you need to fix those too or the basement will still take on water.

How long does a curtain drain last before it needs replacing?

A properly built curtain drain with fabric-wrapped pipe and clean gravel typically lasts 15-25 years before silt buildup or root intrusion reduces its flow enough to need excavation and replacement.

Does a curtain drain need a permit?

Digging the trench itself usually doesn't require a permit, but tying the outlet into a municipal storm drain often does. Check with your local building department before connecting to any public system.

What's the difference between a curtain drain and a French drain around the foundation?

A curtain drain is placed upslope to intercept water before it reaches the house; a French drain runs along the foundation to collect water that has already arrived. Many properties need both.

This is educational information, not engineering advice. Call a licensed drainage contractor or civil engineer if your slope, soil type, or water volume seems beyond a standard DIY trench.