French Drains & Drainage Systems in Mountlake Terrace, WA

Drainage & French drains in Mountlake Terrace: what to know

The city’s stormwater chapter regulates non-stormwater discharges and bans illicit connections. It points to a stormwater manual without naming its edition, and it sets no size or hard-surface trigger for a drainage plan, so we ask the city whether a plan applies to your project before a trench is scheduled. Any grading or drainage exemption tied to project size is confirmed in the code before we rely on it.

Slope interception starts above the wet ground. A curtain drain set across the slope intercepts moisture ahead of the lawn and footing, pitched steadily toward an outlet the lot can handle. Roof water travels through solid pipe that stays apart from the perforated line. Any outlet that crosses into public ground counts as a Type B activity, because the city’s list names stormwater and runoff infrastructure.

Permits and rules in Mountlake Terrace

No trench is opened until we establish whether the drain reaches the public right-of-way and whether the Type B permit extends to the outlet. We confirm with the city whether a drainage plan applies, since the chapter does not set the threshold. The outlet gets its own line in the quote, so each review is visible to the owner.

Rules change and vary by parcel, so we confirm the current requirements with the city before we start.

How we approach it

Site the outlet before sizing any trench
Intercept slope water with a curtain line
Carry roof water in solid line to a dependable exit
Check any right-of-way outlet against the Type B list

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

Questions from Mountlake Terrace homeowners

Which Mountlake Terrace outlets reach the Type B right-of-way list?

An outlet running onto public ground, or connecting to a storm facility, lands on the city’s Type B list, which names stormwater and runoff infrastructure. The city is consulted before an outlet is placed on public ground.

Does the city set a size trigger for a Mountlake Terrace drainage plan?

Not in chapter 16.21, which sets no size or hard-surface trigger. We ask the city whether a plan applies to your project before the trench is scheduled, and we record the answer in the job file.

Which site conditions get surveyed before a side-yard drain is sized in Mountlake Terrace?

We record the outlet’s elevation, the incline above the saturated ground, and the route the water follows out of the yard. Drains go in only where a workable exit is available.