Diagnosing yard drainage problems
- Watch where water goes during a heavy rain — downspouts, low spots, neighbor runoff.
- Check that soil slopes away from the foundation; settled backfill often creates a "moat".
- Extend downspouts and clean gutters before spending on bigger fixes.
Yard drainage fixes: French drains, swales and dry wells
- Regrading: reshaping soil to slope away from the house; check grade with the slope calculator and soil volume with the topsoil calculator.
- Swales: shallow, vegetated channels that carry surface water.
- French drains: perforated pipe in a gravel-filled trench, usually wrapped in filter fabric, that collects groundwater and carries it to a discharge point.
- Dry wells: underground chambers that let collected water soak into the soil — only effective in soils that drain.
Discharge must go somewhere legal — you generally cannot direct water onto a neighbor's property or, in many places, into the sanitary sewer.
Retaining wall types and height limits
Options include segmental concrete block, poured concrete, natural stone, timber and gabions. Every retaining wall needs a compacted base, drainage stone behind it and an outlet for water. Under the International Residential Code (R404.4), walls that are not laterally supported at the top and retain more than 48 in of unbalanced fill must be designed; walls with driveways, slopes or structures above may need design at lower heights. Estimate blocks, base and drainage stone with the retaining wall calculator.
Excavation and site preparation
Drainage and wall projects usually involve trenching and moving soil. Excavated soil swells when dug, so haulers price the loose volume — use the swell option in our cubic yard calculator. Call 811 before digging so underground utilities are marked.
Drainage & Retaining Walls costs in 2026
Costs depend on depth, length, access, soil and discharge point.
| Item | Typical range |
|---|---|
| Exterior French drain | $10–$50 per linear ft (complex up to $100) |
| Interior (basement) French drain | $40–$100 per linear ft |
| Exterior French drain (alternate estimate) | $10–$65 per linear ft |
| Retaining wall | $20–$53 per sq ft of face; average $33 |
| Interlocking block / poured concrete / natural stone | $15–$35 / $20–$40 / $20–$90 per sq ft |
Typical national ranges. New York City and other high-cost metros often run above them — get several written bids for your project.
Calculators for this project
New York rules and permits
New York. Retaining walls above local height thresholds commonly need permits and engineered drawings; frost depth for footings is set locally in each municipality's Table R301.2. In NYC, larger site and drainage work can involve DOB filings and DEP stormwater rules — confirm with the agencies before you build. Residential contractors need a DCWP Home Improvement Contractor license in NYC and county licenses on Long Island.
Frequently asked questions
How much does a French drain cost?
Exterior French drains typically cost $10–$50 per linear foot (complex jobs up to $100) and interior drains $40–$100; other estimates put $10–$65 for exterior drains.
How much does a retaining wall cost?
National cost data show most walls at $20–$53 per sq ft of face with an average of $33 (October 2026).
When does a retaining wall need an engineer?
Under IRC R404.4, when it retains more than 48 in of unbalanced fill without lateral support at the top — and often sooner if there are loads above. Local rules may be stricter.
Where should yard drainage from a French drain discharge?
To daylight, a dry well or another approved outlet — never onto a neighbor's property. Check local rules.
