French Drain Installation in Hillsboro, Oregon: Cost & Process

French Drains in Hillsboro's Valley Clay

Hillsboro sits on the floor of the Tualatin Valley, and that flat valley ground is both the city's strength and its drainage weakness. Washington County's soils are heavy with clay and silt, the water table sits high through the wet months, and the terrain is so flat that water has little natural slope to follow. Put those together with a Pacific Northwest winter that delivers months of steady rain, and you get ground that simply will not drain on its own.

A French drain is one of the most reliable answers to this kind of soil. It is a gravel-filled trench with a perforated pipe at the bottom that collects subsurface water and carries it to a safe outlet — giving water a fast path out of clay that would otherwise hold it for the entire season. This guide explains how French drains are installed in Hillsboro, what affects the cost, and why the valley's flat clay makes them so valuable.

For the full drainage picture, start with our guide to property and site drainage in Oregon. For statewide pricing detail, see French drain cost in Oregon.

When a Hillsboro Property Needs a French Drain

• A chronically soggy yard — Flat clay holds water at the surface, leaving lawns spongy for weeks.
• A wet basement or crawlspace — A high seasonal water table and saturated clay push moisture into below-grade spaces.
• Standing water that will not move — On Hillsboro's flat lots there is little slope to carry surface water away.
• Runoff collecting from surrounding ground — Where everything is flat, water pools at the lowest point instead of flowing off.

How a French Drain Is Installed in Hillsboro

1. Site Assessment and Outlet Planning

Everything begins with where the water will go — and on flat Hillsboro ground, that is the hardest part. The installer evaluates what little slope exists, locates the water source, and identifies a viable outlet: a daylight point, a dry well, or a storm connection. The high water table also gets checked, because it affects how deep the drain can practically go.

2. Trench Excavation

The trench is dug to a steady depth with a consistent downhill slope — and on flat valley ground, maintaining even a 1 percent fall takes care and precise grading. Hillsboro's clay is dense and heavy, it can smear and seal the trench walls, and a high water table can put water in the trench during the dig, all of which the crew manages as they go.

3. Fabric, Gravel, and Pipe

Filter fabric lines the trench — essential in Hillsboro, where fine clay and silt will clog an unprotected drain fast. A bed of clean drain rock goes down, then the perforated pipe (holes down), then more rock, then the fabric folds over the top to seal out sediment.

4. Backfill and Restoration

The trench is backfilled, compacted, and restored to grade. A well-built drain disappears into the landscape within a season while moving water for decades.

Our excavation services cover the precise grading and trenching these flat-lot installations require.

What French Drain Installation Costs in Hillsboro

French drains are priced per linear foot, with the total driven by length, depth, soil, and outlet. Industry baseline ranges commonly referenced include:

Factor	Industry Baseline Range
French drain (per linear foot)	$25–$60
Typical residential run (50–100 ft)	$1,500–$6,000+
Dry well outlet (each)	$1,500–$4,000

In Hillsboro, the cost drivers are the length of the run, the depth a high water table allows, the distance to a workable outlet, and the precision the flat grade demands. Because there is little natural slope, runs are sometimes longer to reach a viable outlet, which raises the total. Only a site assessment gives an accurate number. See French drain cost in Oregon for the broader breakdown.

Why Hillsboro's Flat Clay Makes a Local Eye Matter

On flat valley ground, the outlet and the grade are everything. There is little natural slope to carry water, so the design has to find or create one — and a contractor who works Washington County knows how to do that without over-digging into a high water table. The clay sheds fine silt that will clog an unprotected pipe, so filter fabric has to be used correctly. Get either wrong and the drain holds water instead of moving it. Local knowledge of the Tualatin Valley's soil and water table is what makes the system actually work.

Get Your Hillsboro French Drain Quote

Cojo Excavation & Asphalt installs French drains throughout Hillsboro and Washington County, engineered for the flat, clay-heavy Tualatin Valley ground that makes drainage a genuine challenge. We assess your soil, slope, and water table, plan the right outlet, and give you a real number based on your property.

Request a free drainage assessment and we will respond within 24 hours. Explore our full range of excavation services for Hillsboro-area homes and businesses.