Tacoma Drainage Questions, Answered

Standing water under the house is a drainage problem in any climate, and Tacoma's soils make it a common one. The hardpan under most of the city holds winter rain a foot or two below grade, and a crawl space floor sits right in that zone. The fix is usually a perimeter drain inside the crawl space running to a sump, sometimes with a vapor barrier over the dirt. See the crawl space section under basement waterproofing.

The original footing drain most likely gave out. Houses of that era in the North End, Stadium District, and Proctor were built with clay tile drains, and after a century they clog with roots and silt or shift apart at the joints. Once the drain stops carrying water away, the perched winter groundwater reaches the footing and comes through the wall-floor seam. A new footing drain or an interior perimeter drain restores the escape route.

The outwash gravel under South Tacoma, Parkland, and Spanaway soaks up rain quickly, so groundwater is rarely the cause there. Water getting into a house on that soil almost always comes from the surface: downspouts dumping at the foundation, a driveway or patio pitched toward the house, or a grade that slopes in. Those are the cheapest problems in the trade to fix, and a contractor should rule them out before quoting a trench.

A 1,500-square-foot roof in Tacoma sheds roughly 36,000 gallons a year, and four downspouts emptying beside the foundation put most of it exactly where a drain would have to remove it. Piping roof water to daylight, a dry well on outwash soil, or a permitted storm connection is often the first thing a drainage contractor does, and on some houses it is the only thing needed. Yard drainage covers the options.

Planning ranges: about $2,000 to $7,000 for a yard French drain, about $5,500 to $14,000 for an interior perimeter drain with a sump, and about $6,000 to $15,000 for an exterior footing drain. The three things that push a Tacoma job toward the top of its range are a long run, a deep trench through hardpan, and an outlet that is far away or needs a pump. The cost guide has the full table.

Built with clean drain rock, filter fabric, and a real slope, a French drain in Tacoma should run 30 years or longer. The ones that fail early were laid without fabric in fine glacial silt, or without enough fall, and they choke within a few wet seasons. Ask any contractor to specify the rock, the fabric, and the slope in writing.

Work that stays on your own lot and connects to nothing public generally does not need a City of Tacoma permit. A connection to the City storm system or any work at the curb requires a Stormwater Construction or Repair Permit from Environmental Services, side sewer work needs a Sewer Construction or Repair Permit from Planning and Development Services, and Tacoma Municipal Code 12.08.030 bars groundwater, yard, and roof drainage from the sanitary sewer. Outside city limits, Pierce County Planning and Public Works handles site development review.

Standard homeowner's policies treat seepage, groundwater, and surface water as maintenance and exclude them, so the drainage system itself is nearly always an out-of-pocket improvement. A sudden event such as a burst pipe may be covered, and a water-backup endorsement can help when a sump or sewer backs up. Read the exclusions section of your policy before assuming either way.

A coating on the inside of a wall holds for about one Tacoma winter. The water pressing through is sitting on hardpan outside the wall from December to April, and it moves to the next crack or the cold joint at the floor. Durable fixes collect that water in a drain and remove it with a pump instead of trying to hold it back. Basement waterproofing explains the system.