French drain installation typically costs $20 to $50 per linear foot, depending on trench depth, length, and whether the outlet requires additional grading or a connection to an existing drainage system. Treat every figure on this page as a starting point rather than a quote: a French drain only works if it maintains a consistent downward slope from the problem area to a safe discharge point, and getting that slope wrong is the most common reason these systems fail.
A French drain is a gravel-filled trench with a perforated pipe that collects and redirects groundwater or surface water away from a problem area, typically a foundation, a low spot in a yard, or a chronically wet section of a property. It needs somewhere to actually send that water — a storm sewer connection, a daylight discharge point downhill, or a dry well — and that destination needs to be identified before the trench is dug, not figured out afterward.
What actually drives the price
Trench length and depth are the direct cost drivers, but depth is determined by what the drain needs to intercept — a drain meant to relieve a wet lawn is typically shallower than one meant to intercept groundwater near a foundation, which often needs to be dug down to near the footing depth.
Slope and discharge point matter more than most people expect. A French drain needs roughly a two percent grade along its length to keep water actually moving toward the outlet rather than sitting in the pipe. If the site doesn't have enough natural fall to achieve this over the needed distance, the plan may need a sump pump at the low end instead of relying on gravity alone.
What the trench crosses along its route, driveways, patios, or existing landscaping, adds complexity and cost the same way it does on any utility trench. Confirm the full route before pricing, since a drain that needs to cross a paved surface is a different scope than one that stays in open lawn.
Soil conditions affect both digging difficulty and how well the surrounding native soil will drain into the gravel-filled trench once installed. Heavy clay soil around the trench can limit how effectively the drain actually collects water, which sometimes changes the design to compensate.
Foundation drains versus yard drains
A French drain installed specifically to relieve water pressure against a foundation is a more critical, more precisely engineered installation than a drain meant to dry out a soggy section of lawn. Confirm which type of problem you actually have before scoping the work, since foundation drainage issues sometimes need combined solutions like grading and downspout redirection alongside the drain itself.
A short checklist before you book
Identify a real discharge point before the trench is designed. Confirm the site has enough natural slope, or budget for a sump pump if it doesn't. Map the full trench route and flag any surfaces it needs to cross. Assess whether this is a foundation drainage issue or a general yard wetness issue, since the right fix differs. Confirm pipe and gravel specifications match the volume of water being managed.
Costs vary by site conditions. Use the ranges here to sanity-check what you're quoted, then get a direct price for your own property. If your project needs drainage gravel or stone, Natural Stone Source Ontario can help with supply.
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