The drainage that works below the surface — relieving the water pressure that pushes through foundation walls and lifts basement slabs.
When soil around a foundation saturates, the trapped groundwater exerts pressure on everything below grade — sideways against the walls, upward against the slab. Engineers call it hydrostatic pressure, and in Seattle's wet, slow-draining ground it's the reason foundations leak, walls bow over time, and floors crack and weep. You can't seal your way out of it from the inside; the water has to be given a lower-pressure path away from the structure. That's what foundation drainage does.
Nearly every house built below grade was meant to have a footing drain doing this. The problem, on Seattle's older homes, is that the original system has often quietly failed.
Homes across Seattle's established neighborhoods — Ballard, Wallingford, West Seattle, the older Eastside — were built with clay-tile footing drains: short lengths of unperforated clay pipe laid end to end around the foundation. Two things happen to them over decades:
When a clay-tile footing drain fails, the basement that was dry for fifty years starts leaking, and no amount of interior sealing fixes it, because the water is arriving at the footing under pressure. The repair is a new footing drain — modern perforated pipe, filter fabric, and clean drain rock, run to a proper exit — or, where excavation isn't practical, an interior perimeter system that relieves the same pressure from inside.
A perforated drain at footing depth around the foundation perimeter, intercepting groundwater before it reaches the wall. The direct replacement for failed clay tile.
On sloped lots, a drain uphill of the house that cuts off water crossing toward the foundation. Often the highest-value single move on a Seattle hillside home — it stops the water before the house is even in the picture.
Soil that slopes toward the house, downspouts dumping at the foundation, and hardscape that traps runoff all feed the problem. Correcting grade and getting roof water piped well away is the cheap, foundational first step any good drainage contractor checks before quoting excavation.