French Drains & Drainage Systems in Lynnwood, WA

Drainage & French drains in Lynnwood: what to know

Set across the slope, a curtain drain catches seepage above the lawn and the foundation before it arrives. The trench falls steadily, and the fall is checked with a level at several points. Where flow collects at a flat rear, a French drain takes it on to the outlet, and roof water stays apart from the perforated run in solid pipe.

LMC 13.40.055 adopts the state Stormwater Management Manual for Western Washington, and LMC 13.45.040 sets the discharges allowed into the storm system unless the director finds a pollution risk. The Public Works grading checklist asks that a drainage plan keep existing flow intact with no impact on adjacent properties, so the outlet is chosen to keep water off neighboring lots and the road.

Permits and rules in Lynnwood

Any leg that crosses into public ground or joins a city storm asset is reviewed under LMC 12.04.040 and the storm rules, so the route is mapped on the survey before a trench is staked. Before quoting, we confirm which office holds the review, whether frontage conditions apply, and whether the trench reaches a grading trigger. Each answer is filed with the quote, and the scope waits on any that are still open.

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

How we approach it

Locate the outlet before any trench is laid out
Set curtain drains on a steady fall across the slope
Keep roof water in solid pipe apart from the perforated run
Confirm any right-of-way or storm tie-in before digging

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

Questions from Lynnwood homeowners

Which outlets does Lynnwood’s storm code allow for a yard drain?

Open ground able to absorb the flow, a city storm line that will take it, or a safe low point on the parcel. LMC 13.45.040 governs what may enter the storm system, and neighboring lots and the road are not outlets.

Does a Lynnwood yard drain trench need a grading permit?

The checklist measures cut depth, cut slope, fill volume, and fill depth, so a drain trench is checked against each one before digging, and we confirm the numbers with the counter.

When does a curtain drain fit a sloped Lynnwood yard?

It fits when runoff comes down a slope above and the flat ground below holds it. We map the grade and the path the water takes first, and we recommend a line only where the water has a workable exit.