French Drains & Drainage Systems in Bellevue, WA

Drainage & French drains in Bellevue: what to know

Map where slope water first crosses your lot line, since that is where interception works best. A curtain drain set across the hillside can catch the flow before it reaches the lawn or the footing. Trench alignment follows the contour, and we keep the cut out of ground that is already slipping. Gravel only goes in after a level check proves the run still falls toward the outlet.

Downspout water runs through solid pipe, not perforated line. Bellevue’s guideline asks for natural discharge locations where that is practicable, and runoff may not significantly harm downgradient properties, so the outlet is chosen with the lower neighbor in mind. Outlets stay off the public street and off adjoining lots, and the discharge point is agreed before a shovel enters the ground.

Permits and rules in Bellevue

Any line that reaches the frontage or the public right-of-way may fall under a different review than a backyard drain does. We ask city staff which review governs, and whether a tie to a public line is part of the plan. If the wider project adds or replaces more than 2,000 square feet of impervious surface, the stormwater guideline applies, so we total the roof and drive area before the outlet is chosen. We confirm the outlet with city staff before the trench is laid out.

Bellevue’s permit FAQ requires a permit for a retaining wall over four feet high, counted from the underside of the footing up to the top edge, and for any wall supporting a surcharge load. Walls over 30 inches high must stay out of any required setback. A patio or paver set on grade needs no permit unless the earthwork passes the city’s thresholds, and that exemption does not reach lots inside the Critical Areas Overlay District. The residential right-of-way permit may cover driveway installation and driveway reconstruction or relocation. The city revises these rules, so we confirm the current requirements before work begins.

How we approach it

Locate the point where slope water crosses into the lot
Place the interception run uphill of the wet zone
Carry roof water in solid pipe, separate from the perforated run
Settle the outlet and any frontage review before trenching

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

Questions from Bellevue homeowners

Can a yard drain stand alone in Bellevue, or does the whole project count?

The whole project counts when it adds or replaces more than 2,000 square feet of impervious surface, because Bellevue’s stormwater guideline is measured across the project. We total the roof and drive area before the drain is sized.

What happens to Bellevue drain water that the lot cannot absorb?

Under Bellevue’s guideline, runoff that on-site practices cannot fully manage connects to an outfall under its private single-family drainage rules. The discharge also may not significantly harm the property below, so the outlet is picked with that neighbor in mind.

Would a drain fix the wet ground below a Bellevue slope?

Sometimes, particularly when the water arrives from uphill. We survey grade and soil layers before proposing anything, and a drain goes in only where it reaches the actual source of the seepage.