Excavation
French Drain Installation in Tigard, Oregon: Cost & Process
Cojo
May 30, 2026
7 min read
Tigard sits in the rolling terrain of Washington County, southwest of Portland, where suburban neighborhoods spread across gentle hills and the low ground near Fanno Creek. Through the wet season — late October into April — the Tualatin basin collects steady Pacific rain, and the region's clay-heavy soil holds it stubbornly. Homeowners across Tigard see the familiar signs: spongy lawns, water pooling against foundations, and chronically wet low spots between the slopes.
A French drain is one of the most reliable answers. It is a gravel-filled trench with a perforated pipe at the bottom that intercepts subsurface water and routes it to a lower, safer exit point. On a Tigard lot, where water often runs downhill from neighboring properties and collects in clay that drains slowly, a well-built French drain gives that water a path to follow before it pools where you do not want it.
This guide explains how a French drain is installed on local properties, what the process looks like step by step, and the factors that drive your cost. For statewide pricing ranges, see our French drain cost in Oregon guide, and for the bigger picture, our overview of property and site drainage in Oregon.
Water takes the easiest path. A trench packed with clean drain rock is far more permeable than the surrounding clay, so subsurface water flows into the gravel, drops to the perforated pipe, and runs downhill to daylight or a drywell.
Tigard's soils shape the design. Much of Washington County is underlain by clay and silty clay loam — material that holds water and drains slowly, which is why surface puddles linger and lawns stay soggy. A French drain does not change the clay, but it gives water a fast lane out of the saturated zone. On these soils, depth and a generous gravel envelope matter more than on sandy ground, because the drain has to pull water out of slow-draining material.
Tigard's rolling terrain adds a twist the flat valley floor does not have: water often arrives from uphill. On a sloped lot, intercepting that incoming water before it reaches the house — with a curtain drain across the uphill side — is frequently more effective than a drain at the foundation alone. A contractor evaluates where your water comes from as the first step in the design.
A good installation starts with a site visit, not a phone quote. A contractor walks the property, finds the low points, sees where water collects, traces where it comes from, and identifies where the drain can legally discharge — a downhill slope, a drywell, or a storm connection. On Tigard's sloped lots, mapping both the incoming water and the outfall is the most important step.
With the line laid out, the trench is excavated to the planned depth and slope. A typical yard French drain runs 18 to 24 inches deep; footing and curtain drains go deeper. The trench bottom is graded to fall continuously toward the outfall, verified with a laser level rather than estimated by eye. On a slope, the natural grade often helps establish that fall.
Non-woven filter fabric lines the trench to keep fine clay and silt from migrating into the gravel and clogging the system. In Tigard's clay soils, this fabric is essential — skipping it is the most common reason a French drain fails within a few years. A base layer of clean, washed drain rock goes in first.
A perforated pipe is set on the gravel base with the holes oriented to collect water, bedded to maintain consistent fall to the outfall. Solid pipe is used for any section that only conveys water — such as a downspout tie-in — so it does not leak collected water back into the ground.
More drain rock is placed around and over the pipe, the fabric is wrapped over the top to fully encase the gravel, and the trench is topped with soil, sod, or decorative rock. The finished surface is graded to shed water toward the drain.
Local factors that drive the final number on a Tigard installation:
For statewide pricing ranges and how each factor moves the number, see our French drain cost in Oregon guide. Because every lot differs, the only accurate figure comes from an on-site assessment of your grade, soil, and outfall options.
A French drain is the right tool when the problem is subsurface — a saturated lawn, water seeping toward a foundation, or a chronically soggy low spot. On Tigard's slopes, a curtain drain (a French drain positioned to intercept hillside water) often does more than a drain at the foundation, because it stops the water before it ever arrives. If the issue is surface water that needs capturing at one point, a catch basin or area drain may suit better, and sometimes the best system combines several approaches.
A contractor who assesses your site can tell you which approach actually solves the problem rather than relocating it. The right design depends entirely on where your water comes from and where it can go.
Cojo Excavation & Asphalt installs French drains and full drainage systems for Tigard and Washington County property owners. We start with a site assessment — checking your grade, soil, incoming water, and outfall options — then deliver a clear, no-obligation quote based on what your lot actually needs.
Request a free drainage estimate and we will respond within 24 hours. Learn more about our excavation services and how we help Tigard homeowners and businesses keep water where it belongs.
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