What Is a French Drain?

A French drain is a gravel-filled trench containing a perforated pipe that redirects surface water and groundwater away from problem areas. Named after Henry French, the 19th-century farmer and judge who popularized the concept in his 1859 book on farm drainage, it's one of the most reliable and time-tested drainage solutions in landscaping and civil engineering.

If you have water pooling in your yard after rain, wet basement walls, or soggy low spots that never fully dry out, a French drain may be exactly what you need.

When a French Drain Is the Right Solution

  • Water pools in low areas of your yard after rain
  • Downspouts or sump pump discharge need to be directed away from the house
  • A slope directs water toward your foundation
  • Your lawn has persistently soggy patches that kill grass

French drains are not the right solution for municipal stormwater overload or situations requiring engineered drainage systems — consult a civil engineer for large-scale or commercial applications.

Planning Your French Drain

Find Your Outlet Point

Water needs somewhere to go. Common outlet options include: a dry well (a gravel-filled pit that allows water to percolate into the soil), a storm drain at the street curb, a lower area of your property, or a designated drainage swale. Check local codes — some municipalities restrict where you can discharge yard drainage.

Establish Grade

A French drain requires a consistent downhill slope of at least 1 inch per 8 feet of trench run to function by gravity. Use a string line and line level to map the slope from your problem area to the outlet point before you dig.

Materials Needed

  • 4-inch diameter perforated PVC pipe (with a sock filter, or "slotted pipe in sock")
  • Washed gravel or crushed stone (¾-inch diameter is standard)
  • Landscape fabric (geotextile filter fabric)
  • Sod spade, trenching shovel, or a rented electric trencher for long runs

Step-by-Step Installation

Step 1: Mark and Dig the Trench

Mark the trench path from your problem area to the outlet with spray paint or stakes. Dig a trench approximately 6 inches wide and 18–24 inches deep. Maintain your calculated slope throughout. Dispose of or repurpose the excavated soil — it can be used to build up low spots elsewhere in the yard.

Step 2: Line with Landscape Fabric

Line the bottom and sides of the trench with landscape fabric, leaving generous overlap at the top. This fabric prevents soil fines from migrating into the gravel and clogging the pipe over time — a step many DIYers skip, only to have the drain fail in a few years.

Step 3: Add a Gravel Base

Pour 2–3 inches of washed gravel into the bottom of the lined trench to create a bed for the pipe.

Step 4: Lay the Perforated Pipe

Place the perforated pipe on the gravel bed with the holes facing down. This may seem counterintuitive, but water rises up through the gravel into the pipe from below — placing holes downward allows this while preventing backfill from entering. Connect sections with couplings and ensure the pipe runs continuously to the outlet.

Step 5: Fill with Gravel and Close

Fill the trench with gravel to within 3–4 inches of the surface. Fold the landscape fabric over the top of the gravel to create a complete envelope. Backfill with topsoil, tamp lightly, and re-seed with grass or cover with sod.

Maintenance

A properly installed French drain with landscape fabric should remain effective for many years with minimal maintenance. Occasionally inspect the outlet point to ensure it's clear of debris and not blocked by sediment. If drainage performance degrades after several years, the filter fabric may be saturated with fine particles — in severe cases, the pipe can be flushed with a garden hose or replaced.