French Drain Cost Guide: Materials, Labor, and Installation

A French drain is one of the most effective solutions for yard drainage problems, wet basements, and soggy lawns. Done right, it redirects groundwater and surface runoff away from your foundation or problem areas for decades. Done wrong — with insufficient gravel, undersized pipe, or improper slope — it fills with silt and fails within a few years.

Quick Answer: DIY French drain costs $10–$25/linear foot in materials. You need: perforated pipe, 3/4” clean crushed stone (no fines), non-woven geotextile fabric, and a downslope outlet. Minimum 1% slope — 1 inch of drop per 100 feet — or the drain won’t self-flush.

This guide covers costs, materials, and how to calculate exactly what you need before ordering.

What Is a French Drain?

A French drain is a gravel-filled trench with a perforated pipe at the bottom. Water flows through the gravel, enters the pipe through the perforations, and travels downslope to a discharge point (daylight outlet, dry well, or storm drain).

The name comes from Henry Flagg French, a Massachusetts farmer who popularized the design in his 1859 agricultural drainage manual.

French Drain Cost Overview

Project Type	Typical Cost Range
DIY (materials only)	$10–$25 per linear foot
Professional installation	$25–$65 per linear foot
Basement perimeter (interior)	$50–$100 per linear foot
Exterior yard drain, 50 ft	$750–$2,500 DIY / $1,500–$4,000 contractor

Costs vary significantly by:

• Trench depth and width
• Gravel type and delivery cost in your market
• Whether you’re renting excavation equipment
• Labor rates in your region
• Access to disposal for excavated soil

Materials You Need

1. Perforated Pipe

Standard options:

• 4-inch single-wall corrugated pipe — cheapest, adequate for light drainage
• 4-inch double-wall pipe (ADS) — more durable, maintains round cross-section better
• 4-inch PVC perforated — more expensive but excellent for permanent installations

Cost: $0.50–$1.50 per linear foot depending on type

2. Drainage Gravel

Use 3/4” clean crushed stone — “clean” means no fines. Fine particles will wash into the pipe and clog it.

A typical trench 12 inches wide × 18 inches deep needs approximately 0.5 cubic yards per 10 linear feet of trench.

Use our French Drain Calculator to get exact gravel volume for your specific trench dimensions.

3. Filter Fabric (Landscape Fabric)

Wrap the entire gravel trench in filter fabric to prevent soil migration into the aggregate. Use non-woven geotextile fabric (not woven landscape fabric — the woven type has too large a weave and allows fines to pass through).

Typical: 1.5–2 square yards of fabric per linear foot of trench, depending on trench depth.

4. End Cap and Outlet

The pipe needs either a daylighted outlet (pipe emerges from a slope) or connects to a catch basin or dry well. Budget for a pipe outlet cap and grate: $10–$40.

How Much Gravel Do You Need?

Calculate gravel volume for your French drain:

1. Measure the trench length in feet
2. Measure or estimate trench width (typically 12–18 inches)
3. Measure trench depth (typically 18–24 inches)

Volume = Length × Width × Depth (all in feet, then divide by 27 for cubic yards)

Example: 60-foot trench, 12 inches wide, 18 inches deep:

• 60 × 1.0 × 1.5 = 90 cubic feet
• 90 ÷ 27 = 3.33 cubic yards

Note: Gravel fills only the space not occupied by the pipe. A 4-inch pipe in an 18-inch deep trench occupies about 5% of the volume — small enough to ignore in a rough estimate.

Use our Gravel Calculator for exact volume and weight estimates.

Slope Requirements

A French drain must have slope to function. Minimum slope:

• 1% (1 inch per 100 feet) — absolute minimum
• 1–2% — standard residential
• 2%+ — preferred for reliable drainage

A slope less than 1% risks standing water in the pipe, sedimentation, and eventual failure. Use a level and measuring tape or a laser level to check slope before installing.

DIY vs. Contractor

When to DIY

• Simple yard drainage, not adjacent to the foundation
• You have or can rent a trencher
• Good soil access (no tree roots, underground utilities)
• Project under 50 linear feet

DIY cost breakdown for 50-foot drain:

• Gravel (1.8 cubic yards): $120–$200 delivered
• Pipe (50 LF corrugated): $40–$75
• Filter fabric: $25–$50
• Outlet cap: $15
• Trencher rental (half-day): $150–$200
• Total: $350–$540

When to Hire a Contractor

• Drains adjacent to or around the foundation
• Deep trenching required (over 3 feet)
• Suspected clay soils that require special handling
• Complex systems with multiple branches
• Interior basement drainage

Frequently Asked Questions

How long does a French drain last? A properly installed French drain with clean gravel and filter fabric will last 30–40+ years. The pipe itself is virtually permanent; gravel can be cleaned or replaced if siltation occurs, though this is rare with proper fabric installation.

How deep does a French drain need to be? For surface yard drainage: 18–24 inches deep is typical. For foundation drainage (exterior): the drain should be at or below the footing level, which is below the frost line — often 3–5 feet deep depending on your climate.

Does a French drain need to be perfectly straight? No. French drains can curve to follow lot lines, property edges, or obstacles. Gradual curves are fine; sharp bends should use connectors designed for the pipe type.

What do I do with the excavated soil? You’ll excavate more soil than you’ll put back (the gravel occupies the space the soil came from). Plan to dispose of or spread the extra soil. A 50-foot trench at 12”×18” generates about 3 cubic yards of spoil — roughly 2 pickup truck loads.

Can I install a French drain myself without a trencher? Yes, by hand-digging. A 50-foot trench at 12” wide × 18” deep is about 25 cubic feet per foot = a significant excavation project. Expect 1–2 full days of hard digging for one person. Most rental yards charge $150–$250 per day for a trencher, which makes it very cost-effective for most projects.

---

See also: Excavation Calculation Methodology — volume formulas, bulk density tables, swell/shrink factors, and OSHA trench safety references behind ConstructCalc excavation calculators.