How Is an Exterior French Drain Installed?
An exterior French drain costs $30 to $90 per linear foot installed — a 4-inch perforated pipe bedded in gravel in a trench 12 to 24 inches deep along the foundation, intercepting groundwater before it reaches the wall. It is one of the most effective tools for preventing foundation moisture.
Planning the System
An exterior French drain must have a discharge point: a location where the pipe daylights (exits the ground) at a lower elevation than the collection point, allowing gravity to move the water. The discharge point should be at least 10 feet from the foundation and in a location where the discharged water does not pool adjacent to the home. If no daylighting point exists: a dry well (a buried perforated chamber that allows water to percolate into the soil) is an alternative discharge method for areas with permeable soil. The pipe run must slope consistently from the collection point to the discharge point — at least 1/8 inch per foot of fall (0.5 to 1 percent slope minimum). Mark all underground utilities (call 811 before digging) along the proposed trench route. (For more on this, see Interior vs. Exterior French Drain: Which Do You Need?.)
The Installation Process
Excavate a trench 12 to 24 inches deep and 12 inches wide along the foundation perimeter (or the specific section being drained). Line the trench with filter fabric (geotextile cloth) to prevent soil infiltration of the gravel. Add 2 to 4 inches of clean gravel (1/2 to 3/4 inch washed stone) as a base. Install the perforated pipe (4-inch diameter, with perforations facing down) on the gravel base. Cover the pipe with additional gravel to 4 to 6 inches above the pipe. Fold the filter fabric over the top of the gravel. Backfill with soil to grade. Connect the outlet end of the pipe to the discharge point.
Cost Components
Excavation labor: $15 to $30 per linear foot. Perforated pipe (4-inch): $0.50 to $1.50 per foot. Gravel (3/4-inch washed stone): $25 to $45 per cubic yard (approximately 1 cubic yard per 10 linear feet at 12-inch depth). Filter fabric: $0.10 to $0.20 per square foot. Backfill and compaction: $5 to $15 per linear foot. Total professionally installed: $30 to $90 per linear foot. A 100-linear-foot exterior drain: $3,000 to $9,000.
Working With a Contractor on This Project
Getting the right outcome on any home services project starts before the work begins. A few consistent practices make the difference between a smooth project and a frustrating one.
Get at least two or three quotes. A single quote gives you no basis for comparison. Two or three quotes reveal the market rate for the work, expose scope differences between bidders, and let you assess contractor communication quality before any commitment is made. The lowest bid is not automatically the best value if the scope is thin or the materials are underspecified.
Ask for licenses and insurance before work starts. Verify current general liability insurance and, for any work involving workers on your property, workers compensation coverage. Licensing requirements vary by state and trade; confirm the specific requirements in your jurisdiction. A licensed contractor who carries appropriate insurance protects both parties if something goes wrong during the project.
Get the scope in writing. A written proposal that specifies materials, labor scope, timeline, what is included (permits, cleanup, disposal), and warranty terms is the foundation of a professional engagement. Verbal agreements on any of these points invite misunderstanding. For any project over $500, written scope is non-negotiable.
Clarify the payment schedule upfront. A reasonable payment schedule ties major payments to project milestones: a deposit at signing, a payment at material delivery or project start, and a final payment at completion after a walkthrough confirms satisfaction. A contractor who requires full payment upfront before work begins is a red flag in any trade.
Making a Confident Decision
The information in this article is designed to help you ask better questions of the professionals you work with, evaluate their answers with more confidence, and understand the decisions involved in this type of home services project. It is not a substitute for professional assessment of your specific home.
Every home is different. Roof slopes, local weather, tree exposure, soil conditions, and existing system condition all affect what the right solution is for your specific situation. The general principles here apply broadly, but a professional who assesses your home in person will give you guidance that accounts for the details that general articles cannot.
When you are ready to move forward, getting at least two or three quotes from licensed, insured, local contractors is the most important practical step. It lets you compare approaches, assess contractor quality, and confirm that the solution proposed matches your specific situation and budget.
Ranges here are national ballpark figures, not quotes. Actual pricing varies by region, home condition, materials, and contractor. How we source cost data.
