French Drain Cost Per Foot: What Linear Pricing Actually Includes
Quick Answer (Unit Pricing Summary)
- Exterior yard drain: $15–$45 per linear foot
- Exterior foundation perimeter: $35–$85 per linear foot
- Interior basement perimeter: $50–$120+ per linear foot
Those numbers are accurate — but incomplete.
Cost per foot depends on depth, soil resistance, slab removal, and discharge complexity. A $20/ft system and an $85/ft system are not equivalent in engineering scope.
For full project breakdown (not just unit pricing), see:
french drain installation cost
This page focuses strictly on linear pricing logic.
Interior vs Exterior: Why Per-Foot Cost Varies
Drain Type | Cost Per Foot | Why It Changes |
Exterior shallow trench | $15–$45 | Basic excavation |
Exterior foundation trench | $35–$85 | Deeper dig, more soil load |
Interior perimeter | $50–$120+ | Concrete cutting + trench + sump tie-in |
Interior systems cost more because each linear foot includes:
- Saw cutting slab
- Removing concrete
- Trenching below slab
- Re-pouring concrete
- Integrating with sump basin
Drain configuration overview here:
basement drainage system
If gravity discharge is not possible:
basement-sump-pump-installation
Backup redundancy planning:
battery-backup-sump-pump-installation
Real-World Math Examples
Per-foot pricing only becomes meaningful when multiplied by total length.
Example 1 – Interior System
Basement perimeter: 140 linear feet
Quoted: $75 per foot
140 × 75 = $10,500
If pump + basin adds $2,500 → total ≈ $13,000
Example 2 – Exterior Perimeter
Foundation run: 110 linear feet
Quoted: $45 per foot
110 × 45 = $4,950
Add landscape restoration: $2,000–$5,000
Total likely: $7,000–$10,000
Linear pricing excludes additional elements unless clearly stated.
Depth Multiplier: The Hidden Cost Variable
Per-foot pricing increases with trench depth.
Depth | Cost Adjustment | Why |
12–18 inches | Base rate | Standard yard drain |
24–36 inches | +10–20% | Increased soil removal |
36+ inches | +20–40% | Heavy excavation + safety |
Deeper trenching increases:
- Soil volume removed
- Equipment size
- Labor hours
- Collapse risk mitigation
In colder regions, frost depth requirements raise trench depth further.
Labor vs Material Per Foot
Material cost is relatively stable.
Component | Approximate Per-Foot Cost |
Pipe | $2–$5 |
Gravel | $3–$8 |
Fabric wrap | $1–$3 |
Labor | $10–$70+ |
Labor drives per-foot variability.
In clay soil, trenching may take twice as long as sandy soil. In urban settings, restricted access increases per-foot labor cost significantly.
Soil Impact on Per-Foot Pricing
Soil Type | Impact | Risk Factor |
Clay | +15–30% | Slow percolation + clogging |
Rocky | +20–40% | Slow trenching |
Sandy | Minimal | Easier excavation |
Clay also increases long-term sediment infiltration risk if fabric separation is inadequate.
From reviewing failed installations, improper separation in clay soil is one of the most common reasons drains clog within 5–10 years.
Cheap Per-Foot Pricing vs Proper Installation
Low per-foot bids often exclude:
- Cleanout access points
- Verified 1% slope minimum
- Proper discharge routing
- Redundancy planning
Improper slope leads to sediment buildup.
Frozen discharge lines in cold climates can shut down the system entirely.
Failure cost examples:
Failure | Cost Range |
Clogged trench excavation | $4,000–$12,000 |
Interior slab re-trenching | $5,000–$15,000 |
Mold remediation | $2,000–$10,000 |
The difference between $25/ft and $70/ft often reflects design integrity.
When Per-Foot Pricing Becomes Misleading
Per-foot pricing may not include:
- Corners and directional turns
- Sump basin installation
- Electrical wiring
- Permit costs
- Landscape restoration
- Extended discharge lines
Most basements range between 120–180 linear feet. Small miscalculations multiply quickly.
If active water entry is occurring, stabilize first:
Per-Foot vs Total Project Cost
Per-foot pricing measures excavation and material.
Total project cost includes:
- Pumps
- Basins
- Electrical work
- Grading correction
- Waterproof membranes
Do not compare linear price alone without confirming scope.
Full waterproofing cost context:
Maintenance Economics Per Linear Foot
Longer systems increase:
- Inspection time
- Flushing effort
- Monitoring requirements
Drainage relieves hydrostatic pressure — maintenance preserves that protection.
What This Unit Price Actually Represents
Cost per foot reflects:
- Excavation intensity
- Soil resistance
- Depth requirements
- Concrete involvement (if interior)
- Labor intensity
It does not guarantee performance unless slope, separation, and discharge are correctly engineered.
FAQ
How much does a French drain cost per foot?
Exterior drains typically range from $15–$45 per foot. Interior systems commonly range from $50–$120+ per foot.
Why is interior cost per foot higher?
Interior systems require slab cutting, trench excavation, concrete restoration, and sump integration.
Does trench depth affect cost per foot?
Yes. Deeper trenches increase labor, equipment use, and safety requirements, raising per-foot pricing by 10–40%.
Does soil type impact linear pricing?
Yes. Clay and rocky soils significantly increase excavation difficulty and clog risk.
Does longer length reduce per-foot cost?
In some cases, contractors may offer slight per-foot discounts for long runs, but excavation complexity usually limits large reductions.
Is per-foot pricing enough to compare quotes?
No. Confirm what is included in slope verification, discharge design, and restoration work.