French Drain Guide: Solving Yard Drainage Problems

Updated April 2026 · By the LandscapeCalcs Team

Standing water in your yard is more than an inconvenience — it damages foundations, kills grass, breeds mosquitoes, and makes outdoor spaces unusable. A French drain is the most common solution: a gravel-filled trench with a perforated pipe that collects subsurface water and redirects it to an appropriate outlet. The concept is simple, but the execution requires proper slope, pipe selection, and outlet planning. A poorly installed French drain is just an expensive ditch that does not drain. This guide covers the planning, materials, and installation details that make a French drain actually work.

How a French Drain Works

Water follows gravity. A French drain creates an easy path for subsurface water to flow away from problem areas. A trench is dug with a consistent downward slope, lined with landscape fabric, partially filled with gravel, then a perforated pipe is laid in the gravel with the holes facing down. More gravel covers the pipe, and the landscape fabric is folded over the top before backfilling with soil or additional gravel.

The gravel creates a highly permeable zone that attracts water from the surrounding saturated soil. The perforated pipe collects this water and carries it by gravity to a discharge point — a storm drain, dry well, rain garden, or daylight outlet at a lower elevation on the property.

Planning the Route and Slope

The drain must run from the wet area to a suitable outlet with a consistent downward slope of at least 1 percent — that is 1 inch of drop per 8 feet of run. Steeper slopes drain faster; 2 percent is ideal where the grade allows. Use a line level or laser level to establish the slope before digging.

Identify the discharge point before planning the route. Draining to a storm sewer may require a permit. Draining onto a neighbor's property is illegal in most jurisdictions. A dry well (a buried pit filled with gravel) allows water to percolate into the ground at a chosen location. A rain garden planted at the outlet absorbs and filters the water while adding a landscape feature.

Materials and Pipe Selection

Use 4-inch rigid perforated PVC pipe or flexible corrugated drain pipe. Rigid PVC is harder to install around curves but lasts longer and resists crushing. Corrugated pipe is easier to work with for curved routes but is more prone to clogging and crushing over time. For most residential applications, corrugated pipe with a fabric sock (filter sleeve) works well.

Use clean, washed gravel — #57 stone (three-quarter inch) is the standard choice. River rock works but is more expensive. Do not use limestone or recycled concrete, which can cement together over time and reduce permeability. Line the trench with non-woven landscape fabric to prevent soil from migrating into the gravel and clogging the system.

• Pipe: 4-inch perforated PVC or corrugated with filter sock
• Gravel: #57 washed stone, 3/4-inch, avoid limestone
• Fabric: non-woven geotextile landscape fabric
• Trench: 12-18 inches wide, 18-24 inches deep
• Slope: minimum 1% (1 inch per 8 feet), ideal 2%

Installation Steps

Dig the trench to the planned depth and width, maintaining the target slope throughout. Check slope frequently with a level. Line the trench with landscape fabric, leaving enough excess on each side to fold over the top later. Add 2 to 3 inches of gravel to the bottom of the lined trench.

Lay the perforated pipe on the gravel bed with the holes facing down (for rigid pipe) or with the filter sock intact (for corrugated pipe). Cover the pipe with gravel to within 3 to 5 inches of the surface. Fold the landscape fabric over the gravel. Backfill with topsoil and sod, or leave the top as a gravel-filled trench for a decorative dry creek bed appearance.