French Drains & Drainage Systems in Kirkland, WA

Drainage & French drains in Kirkland: what to know

Kirkland’s drainage review is triggered at 500 square feet of impervious surface, added or replaced, or at 7,000 square feet of land disturbance. Projects that reach either line follow the 2021 King County Surface Water Design Manual and the city’s addendum (KMC 15.52.050 and 15.52.060). A curtain drain or French drain on a sloped lot changes how water moves below it, so its route is checked with the slope and any critical area before the trench is laid.

The outlet decides the design. The city’s code bars non-stormwater discharges into the municipal storm drain system, with listed exceptions, and it prohibits illicit connections. The code does not state whether a private drain can discharge into the right-of-way or the public system, so we put the outlet to Development Engineering before the design is final, and we tie tightlines only where the city confirms the route.

Permits and rules in Kirkland

A drain that changes an existing drainage facility needs city approval and a permit (KMC 15.52.120). Because the code does not say whether a private drain can reach the right-of-way or the public storm system, that question goes to the city first. We check the review thresholds, the outlet, and any critical area on the lot, then tell you which track applies before we dig.

Kirkland’s permit guidance requires a permit for rockeries and retaining walls over four feet. Driveway replacement and any work in the public right-of-way need a Public Works permit. Sidewalks 30 inches or less above grade may not need a building permit when they are not over a basement or story below and not part of an accessible route. Permit exemptions do not apply in areas of flood hazard, wetland, steep slope, shoreline, or other land use critical areas. Rules change, so we confirm the current requirements with the city before we start.

How we approach it

Measure the new impervious area against the 500-square-foot line
Place the interception drain above the wet ground and along the slope
Keep roof lines in solid pipe, separate from the perforated run
Settle the outlet with the city before the trench is opened

For the full process, see our Drainage Systems & French Drains page.

Questions from Kirkland homeowners

What outlet does Kirkland’s code accept for a French drain?

The code does not say whether a private drain can reach the right-of-way or the public storm system, and it bars non-stormwater discharges into the municipal storm drain system except for listed exceptions. We put the outlet to Development Engineering before the design is final.

When does a Kirkland drain project reach the 500-square-foot drainage review?

When it adds or replaces 500 square feet or more of impervious surface, or disturbs 7,000 square feet or more of land, it goes through drainage review under KMC 15.52.050. Changes to an existing drainage facility also need a city permit.

Can an interception drain above a Kirkland slope change the critical area review?

It can, because a steep slope on the lot can bring critical area rules into the review. Runoff descending a slope can call for an interception drain above the yard, and the grade and soil are surveyed before any route is proposed.