Excavation
Foundation Drainage in Hillsboro, Oregon: Keeping Water Out
Cojo
May 30, 2026
7 min read
Hillsboro homes face one of the tougher foundation-water situations in the Portland metro. The city sits on the flat Tualatin Valley floor, where heavy clay holds water against the structure, the water table rises high through winter, and the level ground gives water nowhere to drain. Through months of steady Pacific Northwest rain, the soil around a Hillsboro foundation stays saturated, building hydrostatic pressure that pushes moisture into any below-grade space it can reach.
Foundation drainage is the system that intercepts water before it reaches your structure and carries it to a safe outlet. When it fails or was never installed, you get a wet basement, a damp crawlspace, mold, and over time structural damage. This guide explains how foundation water threatens Hillsboro homes and how to keep it out.
For the broader picture, see our guide to property and site drainage in Oregon. For statewide pricing, see foundation drain installation cost in Oregon.
Hillsboro's clay holds water rather than draining it, so through the wet season the soil against your foundation stays fully saturated. That standing water creates hydrostatic pressure that forces moisture through cracks, joints, and porous concrete.
The Tualatin Valley's groundwater rises close to the surface in winter. When the water table sits near or above the base of a foundation, water is pressing against the structure from below as well as the sides.
On level valley lots, water that reaches the foundation has no natural slope to carry it away. It collects and lingers exactly where it does the most harm.
Roof runoff dumped right next to the foundation is one of the most common and most fixable causes of foundation moisture in Hillsboro, adding concentrated water to an already saturated zone.
The right system depends on the home, the soil, and the water table, so an assessment comes first. Common solutions include:
Our excavation services cover the careful foundation excavation these jobs require.
Foundation drainage is priced by scope — exterior regrading is far cheaper than excavating a full perimeter footing drain. Industry baseline ranges commonly referenced include:
| Work | Industry Baseline Range |
|---|---|
| Exterior footing drain (per linear foot) | $20–$80 |
| Full perimeter foundation drain | $5,000–$15,000+ |
| Interior perimeter drain with sump | $3,000–$12,000+ |
| Exterior regrading | $1,000–$4,000 |
Excavating against a foundation is unforgiving, and Hillsboro adds a high water table and flat ground to the equation. Dig too aggressively next to a footing and you can undermine it; hit groundwater and the trench fills as you work; choose a poor outlet on flat ground and the water has nowhere to go. A contractor who works Washington County evaluates the grade, the clay, the water table, and how water is reaching the structure, then designs a system — exterior, interior, or both — that actually carries water away.
Cojo Excavation & Asphalt protects Hillsboro and Washington County homes from foundation water, with solutions designed for Tualatin Valley clay and a high winter water table. We assess how water is reaching your foundation and recommend the most effective, cost-appropriate fix.
Request a free drainage assessment and we will respond within 24 hours. Learn more about our excavation services for Hillsboro-area homes.
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