French Drains & Yard Drainage in Seattle

A French drain is a trench cut to a consistent fall, containing a perforated pipe surrounded by clean free-draining rock and wrapped in geotextile, which collects water from the surrounding soil and carries it somewhere else. You need one when water has no route out — standing water that persists for days after rain, a lawn that stays spongy all winter, or water collecting against the house. You do not need one if the problem is a single low spot that regrading would fix, or if the issue is roof water that a downspout tie-in would solve for a fraction of the cost. We will tell you when the cheaper answer is the right one.

This is the question that separates a drain that works from one that fails in two years, and it is the first thing we establish. The good outcome is daylight — a discharge point lower than the drain where water can run out freely, which on a sloped Seattle lot is often achievable. Otherwise it is a connection to an approved drainage system. What does not work here is a soakaway pit: the whole reason the garden floods is that the ground will not absorb water, so digging a hole and filling it with rock just relocates the puddle underground. Anyone proposing one on till has not thought it through.

Often it is a large part of the answer, but it depends where the water is entering. Exterior drainage that intercepts surface and shallow groundwater before it reaches the foundation, combined with regrading so the ground falls away from the building and downspouts discharging well clear of it, resolves a lot of crawlspace water. What exterior work will not fix is water coming through a failed foundation or a hydrostatic problem below the drain line — that is a different trade and we will say so rather than sell you a drain that does not address it.

A properly built one — clean rock, geotextile wrap, consistent fall, real discharge point — should run for decades with essentially no attention. The failures we get called to fix are nearly all construction faults rather than age: no geotextile, so soil migrated into the rock and silted the void; an inconsistent fall with dips that hold water; or pipe surrounded by fine material instead of washed rock. If there are catch basins in the system they want clearing of leaf litter once a year, which takes minutes.

It should be, and it is cheaper that way. The machine is already on site, the ground is already open, and the drainage can be designed into the levels rather than retrofitted around them. Doing it later means excavating through work that was just finished. On most of our hardscape projects the drainage is not a separate line item people opt into — it is part of building something that will still be flat and standing in ten years.