What drives French drain cost
Installed cost of a French drain runs $25–$75 per linear foot depending on depth, access, and soil type. A 100-foot exterior surface drain in soft turf can be $2,500. The same linear footage dug deep against a basement foundation (18”-wide trench, 4 feet deep, filter fabric, 4” perforated pipe, washed stone) can hit $7,500–$10,000 because excavation volume is 4x and the work happens adjacent to a structure.
Interior French drains — cut into a basement floor to pipe water into a sump pit — are their own animal. Concrete cut, trench, pipe, gravel, recement: $45–$90/linear foot. A full perimeter interior drain in a 1,500 sq ft basement routinely runs $7,000–$15,000.
Cost breakdown
Excavation ($8–$25/linear ft)
By hand for shallow exterior drains in good soil. Mini-excavator for depths over 24” or any clay. Trench width 12–18”, depth 18”–48”. Rocky soil or tree roots can double this.
Perforated pipe ($2–$4/linear ft)
4” corrugated with sock for light-duty. 4” rigid PVC with holes up for heavy-duty or long runs. SDR-35 solid pipe ($3–$5/ft) for runs that transition from drainage to discharge without infiltration.
Drainage gravel ($50–$90/ton)
Washed #57 or #8 angular stone. A 100-ft trench at 18” wide by 24” deep needs about 12–14 tons. That’s $700–$1,200 in gravel alone, plus delivery.
Filter fabric ($0.30–$0.80/ft)
Non-woven geotextile lines the trench to keep silt from clogging the gravel. Non-negotiable — a French drain without fabric clogs within 5–10 years.
Cleanouts ($80–$200 each)
Vertical risers every 50–100 feet for flushing the system. Often overlooked by cheap installers.
Discharge termination
- Daylight outlet ($200–$600): Pipe slopes to an exit in a lower area of the yard. Cheapest and most reliable — gravity does the work.
- Dry well ($500–$1,500): Buried gravel-filled pit that lets water percolate away. Works where there’s no lower ground.
- Sump pump integration ($800–$2,500): Drain feeds a sump basin; pump discharges above grade. Required for interior drains and for exteriors on flat lots.
- Storm sewer tie-in ($400–$1,500): Connects to municipal storm drain. Permit required in most cities.
Exterior vs interior
Exterior is always preferred when possible: it intercepts water before it reaches the foundation. Costs $30–$60/ft. Requires excavating to the footing (4–8 feet) and backfilling — landscaping, walkways, and decks in the way drive the price up fast.
Interior is the rescue option for existing finished basements where you can’t dig outside without demoing hardscape. It doesn’t stop the water from hitting the foundation, but it catches it where it enters and pumps it out. $45–$90/ft.
Sump pump sizing and integration
Standard 1/3 HP submersible pump ($150–$400) handles typical basement load. 1/2 HP ($250–$600) for heavy infiltration or high head. A battery backup pump ($400–$900 installed) is essential because power outages often accompany the storms that flood basements. Whole-system with primary + backup + battery + alarm: $1,500–$3,000 installed.
Regional variation
- Southeast, Midwest: $28–$55/ft exterior. Heavy rain regions with clay soils.
- Northeast: $40–$75/ft. Frost depth requires deeper trenches.
- Pacific Northwest: $35–$65/ft. High demand, experienced installers.
- Southwest, mountain states: $25–$50/ft. Generally less needed except in specific micro-conditions.
- California: $45–$85/ft. Permit overhead, higher labor.
DIY vs pro
A surface-level yard drain (under 24” deep, no foundation contact) is the most DIY-friendly drainage project in residential construction. Rent a trencher for $200/day, buy pipe, fabric, and gravel, and you’ll save 50–60% versus a contractor — assuming you’re OK with a weekend of hard labor. Anything deeper than 30”, anything along a foundation, any interior drain, and any job that needs a permit should be pro.
Common mistakes
- Wrong slope. Pipe must fall at least 1% (1/8” per foot). Flat pipe fills with silt and stops draining.
- Skipping filter fabric. Saves $50 today, costs $5,000 in 8 years when silt clogs the gravel.
- Terminating at the foundation. Discharge must be 10+ feet from the foundation, ideally to daylight.
- Undersized pipe. 3” pipe clogs; use 4”. For long runs or heavy flow, use 6”.
- No cleanout access. System eventually silts up. Without cleanouts, you can’t flush it.
When to call a pro
Any interior drain, any foundation-depth exterior, any project on a slope over 15%, and any drain that ties into a storm sewer. Get three bids and ask each to itemize: trench dimensions, pipe type, gravel tonnage, fabric, cleanout count, and discharge method.