Bellevue ADU rules — what changed under HB 1337
Bellevue updated LUC 20.20.120 to comply with state law. Here is what's actually different on the ground.
The Bellevue baseline
Bellevue Land Use Code 20.20.120 governs accessory dwelling units. Under the post-HB-1337 update, single-family lots in R-1 through R-7.5 zones may host one AADU and one DADU concurrently, with no owner-occupancy requirement and no off-street parking required within a half-mile of frequent transit.
Maximum DADU size is 1,000 square feet of gross floor area; height limits follow the underlying zone (typically 30 feet) with the same dormer and pitched-roof bonuses available to the primary residence.
Sources:City of Bellevue
Where Bellevue still differs from Seattle
Design-review thresholds are higher in Bellevue's mixed-use districts. Tree retention rules in the R-1 zone are stricter, with a higher percentage of significant trees required to be retained on conforming lots.
Stormwater follows Ecology's 2019 manual via the City's Clearing & Grading Code — the trigger thresholds are slightly higher than Seattle's, which often makes Bellevue lots cheaper to develop on the sitework line.
Sources:Municipal Research and Services Center of Washington
Practical advice for Bellevue owners
Pull a pre-application meeting before design starts — Bellevue staff will walk through tree, stormwater, and setback issues in a single sitting and the meeting is free. Confirm sewer capacity early; some 1950s-era subdivisions have undersized laterals that will not accept a second unit without replacement.
