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Sitework & Earthworkaka: perimeter drainaka: drain tileaka: footing drainaka: subsurface drain

French Drain

In Plain English

A gravel-filled trench with a perforated pipe that collects and redirects underground or surface water away from a building.

Definition

A trench filled with gravel or rock containing a perforated pipe that redirects surface water and groundwater away from areas where it would cause problems. French drains are used for foundation drainage, landscape drainage, and surface water management. The perforated pipe collects water through small holes, and the gravel provides a path for water to flow into the pipe.

Why It Matters in Bidding

French drains appear in both site and foundation scopes, and ambiguity over which trade owns them is a common source of scope gaps at bid time. Estimators must verify trench length, gravel volume, filter fabric, perforated pipe, and outfall connection, because under-counting any component or missing the discharge point can turn a small line item into a costly change.

Example

Reviewing the civil and architectural sets together, an estimator caught that the foundation perimeter French drain on the architectural detail wasn't shown on the civil grading plan and issued an RFI to clarify whose scope carried the gravel and filter fabric.

Related Terms

DewateringSwaleGeotextileGravel

Frequently Asked Questions

It depends on location. Foundation-perimeter drains are often the excavation or foundation sub's scope, while site or landscape drainage falls to the sitework contractor. Because details can appear on architectural, structural, and civil sheets, estimators should confirm assignment in writing to prevent both double-counting and uncovered scope at award.
A complete takeoff includes trench excavation by linear foot and depth, washed gravel or stone by volume, filter fabric to wrap the aggregate, perforated pipe, cleanouts, and the connection to a daylight outfall, dry well, or storm system. The discharge point is frequently overlooked and can carry significant added cost.
When the design omits a positive outfall or the drain ties into an undersized storm system, field crews must add piping, sumps, or pumps not in the bid. Differing groundwater conditions can also force a deeper trench, so estimators should price based on the geotech water table rather than plan depth alone.

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