Bellevue ADU rules

✓ Verified against code · August 19, 2026

Current rules under LUC 20.20.120 (Land Use Code), adopted by Ordinance 6851, in effect since July 1, 2025. Detached ADUs were prohibited entirely in Bellevue until Ordinance 6851 (adopted June 24, 2025, effective early July 2025). The 2023 ADU reform (Ord 6746) removed owner-occupancy and registration for attached ADUs only — it did not legalize DADUs, despite what several guides claim. Anything describing Bellevue DADU rules with a pre-July-2025 date is describing a prohibition.

Common questions, answered from the code

Can I build a detached ADU (backyard cottage) in Bellevue?

Yes — since July 2025. Detached ADUs were prohibited in Bellevue until Ordinance 6851 took effect. You can now build up to two ADUs per lot, including detached ones up to 1,200 sq ft and 24 ft tall. Note that the City of Bellevue's own older ADU-reform page still describes DADUs as not allowed — it predates the ordinance.

LUC 20.20.120 (Ord 6851, June 24, 2025) · Permalink

How big can a Bellevue ADU be?

1,200 sq ft, excluding up to 300 sq ft of parking or unheated storage. Several national guides state 1,000 sq ft — that's the state-law floor, not Bellevue's adopted limit.

LUC 20.20.120.C.3 · Permalink

Do I need parking for a Bellevue ADU?

Not if the ADU is under 1,000 sq ft, and not if you're within a half mile of a major transit stop. Otherwise, one space in addition to the main house's parking.

LUC 20.20.120.C.5 · Permalink

Do I have to live on the property to rent out an ADU in Bellevue?

No. Bellevue removed owner-occupancy in July 2023 (Ordinance 6746), two years before the state deadline.

Ord 6746 §1 · Permalink

Are Bellevue's pre-approved DADU plans available yet?

No. The program is in development, with up to ten plans anticipated in 2026 tied to the next state building code adoption. Sources claiming Bellevue already offers approved plan sets with fast-track permitting are contradicted by the city's own program page.

bellevuewa.gov pre-approved plans page · Permalink

Attached or detached — which is easier under Bellevue zoning?

Attached, on the numbers: attached ADUs are fully exempt from floor-area-ratio limits and unit counts, while detached ADUs count toward both. If your lot's FAR budget is tight, an attached ADU may fit where a DADU won't.

LUC 20.20.390.A–.B · Permalink

The rules at a glance

ADUs allowed per lot	Two ADUs per lot in any district that allows a single-family dwelling — attached, detached, or a mix. No new ADU on a unit lot created by unit-lot subdivision.LUC 20.20.120.C.1, .C.7Previously: Detached ADUs were prohibited entirely; attached only — changed by Ord 6851, adopted June 24, 2025
Maximum size	1,200 sq ft maximum per ADU. Up to 300 sq ft of parking or unheated storage per ADU is excluded. The Director may approve more for a single-floor attached ADU, an addition to an existing detached accessory structure, or a conversion; guest-cottage conversions are exempt from the cap.LUC 20.20.120.C.3
Detached ADU height	24 ft to the highest point for a detached ADU; 28 ft when built as an addition over an existing accessory structure. (Principal units get 32–35 ft.)LUC 20.20.120.E.1; Table 20.20.538.C.1 fn 9
Detached ADU setbacks	Same dimensional standards as middle housing: side 5 ft; rear 15 ft (LL-1 through SR-2 districts) or 10 ft (SR-3 through MDR-2); front 10–25 ft by district. A DADU may be sited at a lot line that abuts an alley. Conversions of existing structures are allowed despite nonconforming setbacks.LUC 20.20.120.E.2, .C.4; Table 20.20.538.C.1
Off-street parking	None for ADUs under 1,000 sq ft; none within a half mile of a major transit stop; otherwise one space per ADU in addition to the primary structure's spaces.LUC 20.20.120.C.5, .B.1
Owner-occupancy	None. Removed by Ordinance 6746 in July 2023 — owners are not required to live on site, and the separate ADU registration was abolished at the same time.Ord 6746 §1
Lot coverage / floor area	Lot coverage 40–45% by district (the middle-housing table applies to DADUs). FAR treatment is asymmetric: attached ADUs are fully exempt from FAR and unit counts, while detached ADUs count toward both — making attached units 'cheaper' in zoning currency.LUC 20.20.390.A–.B; Table 20.20.538.C.1 fns 5, 10
Permit path & timeline	Permitted use — no conditional use permit and no ADU registration. Built under a standard building permit. The city publishes no ADU-specific review timeline; secondary sources suggest roughly 4–6 months for custom single-family-track review (estimate only).LUC 20.20.120.C.2, .C.4

Worth knowing

Bellevue is the newest DADU market in the region — detached ADUs were illegal here until mid-2025, so almost no local DADU precedent or content exists.
ADUs can be sold separately via unit-lot subdivision (LUC 20.45A.065 / 20.45B.057).
An ADU cannot coexist with a Home Occupation Permit business on the same site (LUC 20.20.120.C.6).
A pre-approved DADU plan program is in development (up to ~10 plans, launch anticipated 2026) but is NOT live yet — claims that Bellevue already has approved plan sets are wrong.

On our watchlist

Pre-approved DADU plan program launch anticipated in 2026, tied to the next state building code adoption. Watch for housekeeping Land Use Code amendments following Ord 6851.

Check your parcel

The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:

Primary sources

Other Washington cities

Bothell · Burien · Edmonds · Everett · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Redmond · Renton · Sammamish · Seattle · Shoreline · Tacoma

Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.