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Most people ask how long the trench is. The question that actually sets the price is where the water goes when it leaves the pipe.
A French drain in Washington County typically runs between $3,000 and $12,000 installed, but that range is nearly useless by itself. The number that actually matters is how far you are from a workable outlet — and most homeowners never hear that until the crew shows up. Beaverton Excavation Co. sees this pattern constantly: two jobs that look identical on paper come in at very different prices because the discharge options are completely different.
The single biggest cost driver on flat Tualatin Valley ground is outlet distance, not pipe length. A 40-foot French drain with no place to discharge costs more than a 100-foot drain that daylights 20 feet away in the neighbor's swale or at the curb. When there is no outlet, the contractor either has to run a much longer trench to find one, install a dry well to absorb the water, or bring in a sump pump — all of which add cost. A bid that prices the job purely per linear foot of pipe, without walking the property to find where the water goes, is guessing.
This is the factor that surprises people the most. Gravity drains need somewhere to go. A short pipe that collects the water beautifully but dead-ends in another flat lawn has just relocated the problem. If daylight is close and at a lower elevation, the job is straightforward. If the only available outlet is across the yard, under a driveway, or out to a street that sits higher than your lawn, the trench run gets longer and the cost goes up accordingly. In some cases there is no gravity outlet at all, and a completely different solution is needed.
Standard French drains sit 18 to 36 inches deep. Deeper installations catch more groundwater but also move more soil, require wider trenches for safe working conditions, and take longer to backfill and compact properly. On the valley floor, deeper also increases the chance of hitting the seasonal high water table during installation, which slows the work. Every additional foot of depth adds labor and haul-off cost.
Parts of Washington County have basalt close to the surface — sometimes two or three feet down. A machine that cuts through silty clay all day stops dead in basalt. Rock work requires a different bucket, slower progress, and sometimes blasting or jack-hammering, depending on how solid the formation is. There is no way to price this risk accurately without knowing what your specific yard is sitting on. A contractor who has worked nearby can give you a better-informed estimate than one who hasn't.
A compact excavator makes French drain installation fast and predictable. If your backyard is only accessible through a 36-inch gate, or if there is a deck, a mature tree, or a buried irrigation system in the way, some or all of the trench may need to be hand-dug. Hand work runs significantly higher per linear foot because it is slow. The difference between full machine access and a fully hand-dug job on 80 feet of trench can easily be $1,500 to $2,500.
Digging a trench through an established lawn creates a scar. Basic restoration — grading the backfill, seeding, and straw — is usually included in a complete job quote. Sod replacement, irrigation repair, or replanting ornamentals are add-ons that get priced separately. If you have an irrigation system, mark the heads and lines before any crew arrives, and expect that some heads will need to be relocated after the trench is filled.
Tualatin Valley silty clay is the dominant soil across most of Beaverton and the surrounding flatlands. It is dense, holds water well into spring, and does not drain quickly under any circumstances. This matters for cost in two ways. First, the excavated spoil is heavy — wet clay weighs significantly more than dry sandy soil, which means haul-off truck trips and tipping fees are higher. Second, the trench walls in saturated clay can slump, especially in late winter and early spring, which adds time and sometimes shoring cost on deeper installations.
Beaverton sits on a flat valley floor, not on a slope. Slope is your friend when it comes to drainage — it makes finding an outlet easy and keeps installation straightforward. On flat ground, every foot of outlet distance costs more to achieve, and sometimes the ground is so level that a gravity drain simply cannot work. When neighboring properties, streets, and swales are all at approximately the same elevation as your yard, the contractor has to get creative, and creative costs more.
The wet season runs roughly October through May in Washington County. Jobs scheduled in December or January may involve working in standing water, which slows progress and increases machine wear. Some contractors factor a weather premium into winter work; others simply decline jobs during the wettest months. If you are getting quotes, ask whether the price changes based on time of year.
Before you get a quote, spend twenty minutes with a garden hose or during the next rain event. Watch where the water comes from and, more importantly, where it wants to go. A low spot in the lawn with water visibly sheeting toward it from higher ground is a candidate for a French drain. A low spot where water just sits with nowhere obvious to go raises the outlet question immediately.
Walk your property line and locate the lowest accessible point. Is there a ditch at the road? A swale in a neighboring easement? A storm drain at the curb? Measure the rough distance from the wet area to that point — that is the minimum pipe run you are looking at. If the only candidate outlet is actually uphill from the wet spot, mark it as a problem to discuss with a contractor before any work begins.
Check for any utilities or structures between the wet area and the outlet. Irrigation lines, downspout connections to underground pipes, and old septic laterals are common surprises in established Washington County neighborhoods. Call 811 before anyone digs — it is free, legally required, and marks public utilities. Private lines are your responsibility to locate.
A quote given entirely over the phone based on square footage or a rough description of the problem is not a real number — it is a placeholder. French drain pricing is site-specific in a way that most other landscaping work is not, because the outlet situation varies enormously from property to property even on the same block.
A contractor worth hiring will want to walk the property, identify where the water is coming from, and trace a potential outlet route before quoting. If they do not ask about your outlet options, ask them directly: "Where does the water go when it leaves the pipe?" The answer tells you whether they have actually thought through the job.
Our drainage and French drain services page covers what a site visit typically involves, including how we evaluate outlet options before recommending a solution. Regrading the surrounding area is often done at the same time as the drain install, which can reduce total mobilization cost compared to scheduling two separate visits.
A 200-foot French drain in Washington County typically runs $6,000 to $16,000 or more, depending on depth, outlet distance, machine access, and soil conditions. Tualatin Valley clay is heavy and slow to excavate, which raises labor costs. A long pipe run also means the outlet situation becomes a major cost factor — if daylight is not available at the far end, you need a dry well or pump, which adds to the total.
Most 100-foot French drain installations in the Beaverton area land between $3,500 and $8,000. The wide range comes from outlet distance, trench depth, and access. A 100-foot drain with a nearby daylight outlet and full machine access is a straightforward job. The same 100 feet with no outlet, a tight gate, or rock a few feet down can cost significantly more.
Nationally cited averages typically range from $10 to $30 per linear foot, but those figures often exclude outlet work, haul-off, and restoration. In Washington County, where clay soil is heavy and flat valley terrain makes outlets harder to find, a complete installed job with all costs included more often lands between $4,000 and $10,000 for a typical residential project. Always get a quote based on a site visit, not per-foot pricing alone.
It depends on what your site requires. A simple drain with a nearby outlet and full machine access is a reasonable cost for the problem it solves. The expense climbs when you need a long run to reach an outlet, when basalt or saturated clay slows excavation, or when hand-digging is required due to access. Getting a site-specific quote rather than a per-foot estimate is the only way to know what your situation will actually cost.
Renting a trencher and buying perforated pipe is achievable for some homeowners on accessible, obstacle-free ground. The limiting factor is usually the outlet — a DIY trench that dead-ends without a proper discharge point just moves the problem. Before renting anything, confirm where the water will exit the pipe and that the outlet point is lower than your starting point. Hitting an unmarked irrigation line or gas line is the most common DIY injury; call 811 first.
Solving a drainage problem that buyers would notice — a chronically wet basement wall, a yard that holds water for days — generally helps a sale more than it costs. It removes a red flag. That said, drainage improvements rarely appear as a line-item value add the way a kitchen remodel might. The real return is avoiding foundation damage, mold problems, and buyer concerns that would otherwise reduce your sale price or kill a deal entirely.
Most of these questions have a general answer and a site-specific answer, and the site-specific one is the one that decides the cost. If you want a real number for your property, call (458) 272-9359 or send the details and we will walk the ground with you.