Excavation
French Drain Installation in Sherwood, Oregon: Cost & Process
Cojo
May 30, 2026
7 min read
Sherwood has grown quickly from a small Washington County town into a thriving community of newer hillside subdivisions south of Tualatin. That growth has put many homes on graded slopes and cut-and-fill lots near the Tualatin River and Cedar Creek, where water management is built into the development but does not always keep up with the realities of the Pacific Northwest wet season. Combined with the heavy clay common throughout western Washington County, Sherwood properties frequently see water collecting where it should not.
A French drain is one of the most reliable tools for moving subsurface water off a property. It is a perforated pipe set in a gravel-filled trench, wrapped in filter fabric, that collects groundwater and carries it by gravity to a lower discharge point. On Sherwood's hillside lots, gravity drainage is often achievable, but graded slopes can also send water from one property toward another, and clay soils demand careful construction. A French drain built for these conditions can solve persistent water problems for years.
The process is methodical, and each step matters in Sherwood's clay and graded terrain.
Before digging, we evaluate where water comes from, where it collects, and where it can discharge. The drain has to run continuously downhill to a daylight outlet, a dry well, or a storm connection. On Sherwood's sloped subdivision lots, a gravity outfall is frequently available, and identifying it is the first step.
We dig a trench along the planned route, deep and wide enough to surround the pipe with a generous gravel envelope. The trench is graded to maintain a consistent fall, usually around half a percent to one percent, so water keeps moving and sediment does not settle.
In Sherwood's clay soils, filter fabric lines the trench to keep fine particles from migrating into the gravel and pipe. This is the most important step for long-term performance in heavy clay.
A bed of drain rock goes down first, then the perforated pipe positioned to collect water efficiently, then more gravel surrounding and covering it. This forms the permeable channel that draws water in.
The fabric is folded over the gravel, the trench backfilled, and the surface restored, with the outlet set to daylight cleanly or tie into its destination.
Western Washington County around Sherwood receives well over 40 inches of rain a year, concentrated in the cool months when the ground stays saturated for weeks. The clay soils drain slowly and hold water near the surface. Sherwood's newer subdivisions sit on graded, hilly terrain, which means cut-and-fill slopes that can channel water toward homes and create seepage at the base of slopes.
On hillside Sherwood lots, an uphill curtain drain to intercept slope water often works alongside a French drain. The graded nature of many subdivisions also means a property may receive water from neighboring lots above it, so understanding the full drainage pattern matters. In heavy clay, any buried system needs a robust gravel envelope and quality fabric to last. Our French drain cost in Oregon guide explains how these factors shape pricing.
French drain pricing is usually quoted per linear foot, with industry baseline ranges typically running from roughly $25 to $60 per linear foot for residential work. Where your project lands depends on:
Published ranges are a starting reference, not a quote. Actual Sherwood projects can exceed baseline figures when clay excavation or hillside interception is involved. The reliable number comes from a site assessment.
Every Sherwood property drains differently. A home at the base of a graded slope has different needs than one at the top of a subdivision. An on-site evaluation lets us trace where the water originates, including whether it arrives from neighboring lots, confirm a workable outfall, and decide whether a French drain is the best tool, or whether a curtain drain, swale, or area drain would serve you better.
Installing a French drain on a guess is how systems end up clogged, undersized, or daylighting to nowhere. A contractor who walks your property and checks the slope and soil will design a system that actually moves your water for years.
If water is collecting where it should not, a properly built French drain can solve it for the long haul. Cojo Excavation & Asphalt provides free, no-obligation drainage assessments for Sherwood homeowners and property managers. We evaluate your soil, slope, and outfall options, then deliver a clear plan and transparent quote.
Start with the big picture in our guide to property and site drainage in Oregon, then learn more about our excavation services and how we solve drainage problems across Washington County.
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