Seattle Drainage Questions, Answered

Almost always a failed original clay-tile footing drain — it clogged with roots or collapsed, so the groundwater it used to carry away now reaches the foundation. Nothing changed inside; the buried drain that protected the house quietly stopped. The fix is a new footing drain or an interior perimeter system.

In Seattle's low, near-sea-level neighborhoods the water table can rise above the basement slab in a wet winter, so pressure comes from below. That's a sump-and-perimeter-drain situation — a coating can't hold back water pushing up through the floor.

Often more than you'd expect. A Seattle roof sheds a huge volume of water, and downspouts emptying at the foundation are a leading cause of "basement" leaks. Piping that water away is one of the cheapest fixes in the trade and sometimes solves the problem on its own — which is why a good contractor checks it first.

Built right — clean rock, filter fabric, proper slope — 30 years or more. The early failures in Seattle skipped the fabric and rock and silted up in a few seasons. It's a materials-and-install question, not a design one. Ranges for every job are in the cost guide.

Yard and perimeter drainage often doesn't; storm-system tie-ins, grade changes on regulated steep slopes, and work in critical areas (common on Seattle's hillsides) can. A real contractor knows the thresholds and pulls what's required — city or county.

Usually not — standard policies exclude gradual groundwater and surface-water intrusion as maintenance. A sudden burst-pipe event may be covered, and a water-backup endorsement helps with sewer/sump backups. The drainage system itself is generally an out-of-pocket improvement.

On a basement with pressure behind the wall, a sealer buys about a season. Saturated soil (and, in low neighborhoods, a high water table) keeps pushing water through to the next seam. The durable fix collects and pumps the water rather than holding it back — see basement waterproofing.