Bellevue ADU Rules (2026): Size, Setbacks, Parking & DADU Guide

ADU Regulations in Bellevue, Washington

Updated September 29, 2026

Detached ADUs only became legal in Bellevue on 1 July 2025, when the city's Middle Housing amendments (Ordinance 6851) took effect. Bellevue had already reformed its ADU rules in 2023 (Ordinance 6746). Together those two ordinances deleted most of the restrictions that older guides still repeat.

Below is a summary of the key zoning rules applicable to Accessory Dwelling Units in Bellevue as of 2026. Regulations are governed by the Bellevue Land Use Code (LUC 20.20.120, with dimensional standards in LUC 20.20.538) and Washington's statewide ADU law, RCW 36.70A.680 and 36.70A.681.

Additional Local Requirements for Bellevue

• Up to 2 ADUs per lot in any zone where a single-family home is allowed — two attached, one attached plus one detached, or two detached units
• Detached ADU height limit: 24 ft, or 28 ft when built as an addition over an existing accessory structure
• No design review and no ADU registry: additional design controls and the registration/noticing requirements were removed in 2023
• Converting a detached garage, studio or other existing structure is allowed even if that structure does not meet current setback or lot coverage rules
• Impact fees are capped at 50% of what the main house would be charged (RCW 36.70A.681)
• An ADU may now be sold separately from the main house; the old condominium prohibition was lifted
• A property cannot have both an ADU and a home-occupation business, and new ADUs are not allowed on unit lots created by unit-lot or short subdivision
• Short-term rentals may still be regulated by the city — check before counting on nightly-rental income

Bellevue ADU rules changed twice in three years

Two ordinances explain why so much Bellevue ADU information online is out of date:

• Ordinance 6746 (2023) — the ADU reform package. Bellevue repealed the owner-occupancy requirement, removed ADU design controls, dropped the registration and noticing process, and lifted the ban on selling an ADU separately from the main house.
• Ordinance 6851 (adopted 24 June 2025, effective 1 July 2025) — Middle Housing. This is the change that matters most: before it, detached ADUs were not allowed in Bellevue at all. The middle housing amendments legalised them and allow up to two ADUs per lot, implementing Washington's HB 1110 and HB 1337.

Practical consequence: if an article tells you Bellevue requires the owner to live on site, caps an ADU at 1,000 sq ft, or that you cannot build a detached unit, it was written before mid-2025 and is describing rules that no longer exist.

What you can build in Bellevue: the 2026 limits

Two narrow limits are worth knowing early: a site cannot contain both an ADU and a home-occupation business, and no new ADU can be built on a unit lot created through a unit-lot or short subdivision.

Can I add an ADU to my existing Bellevue house?

Yes, and this is the cheapest route. An attached ADU (basement, converted garage, upper-floor addition) follows the main house's height and setback limits, and its floor area is not counted against the site's single-family floor-area allowance — so a big addition does not eat your FAR.

Conversions are the hidden advantage in Bellevue: the code lets you convert an existing structure into an ADU regardless of whether that structure currently meets the applicable setback and lot coverage dimensional requirements, and doing so does not make the property legally non-conforming. In most cities, a garage that sits too close to the property line is the reason a conversion fails. In Bellevue it is not a blocker.

Can I build a DADU (detached ADU) in Bellevue?

Since 1 July 2025, yes. Detached units are limited to 24 ft in height, or 28 ft when proposed as an addition over an existing accessory structure, and they follow the middle-housing dimensional table in LUC 20.20.538 (10 ft front, 15 ft rear, 5 ft side in the single-family zones). A detached ADU may be sited on the lot line that abuts an alley, which is how narrow lots usually make the numbers work.

Watch for one confusion that catches even experienced designers: the old detached accessory structure rules (LUC 20.20.125 — 5 ft rear setback, 15 ft height, 10% lot coverage) do not apply to detached ADUs. Mixing the two produces the wrong setback and the wrong height limit, which is exactly the mistake this page used to contain.

Parking, owner occupancy and design review: three rules people get wrong

• Parking is not simply waived. Bellevue requires no off-street space for an ADU under 1,000 sq ft, or for one within 1/2 mile of a major transit stop. Outside those cases, one space per ADU is required. State law also caps what a city may ask: no parking within a 1/2-mile walk of a major transit stop, at most 1 space on lots under 6,000 sq ft, at most 2 on larger lots.
• Owner occupancy is gone. The city repealed it in 2023 and RCW 36.70A.681 independently forbids cities from requiring the owner to live in the ADU or the main house.
• Design review is gone. An ADU cannot face design or aesthetic requirements stricter than those applied to a single-family house, and Bellevue removed its extra design controls in 2023.

Which Bellevue building permit you need, and how the process runs

• 1 or 2 units on the lot: a standard one- and two-family residence building permit.
• 3 to 6 units in a single structure: the Middle Housing permit process.
• More than 6 units: the commercial multifamily process.
• ADUs count as dwelling units for this test, so adding a second ADU can push a project into the middle housing path.
• One building permit is issued per building; a multi-building project may also need a separate clearing and grading site permit.
• There is no ADU registry and no noticing requirement — that step was removed in 2023.

Start with a pre-application conversation with Bellevue's Development Services before you pay for drawings. Ask two questions that change projects: whether the lot carries a home-occupation business, and whether it was created by a unit-lot or short subdivision — either one can rule out a new ADU.

One amendment to watch

Ordinance 6931, passed on 28 July 2026, amends the units-per-lot provisions in LUC 20.20.120(C)(1) and 20.20.538(C)(1). It was pending codification at the time this page was written. If your project depends on the exact number of units you can build, confirm the current count with the city rather than relying on any guide, including this one.

Frequently Asked Questions About ADUs in Bellevue

Can I build an ADU in Bellevue?

Yes. Bellevue allows up to two ADUs on any lot zoned for a single-family home, and since Ordinance 6851 took effect on 1 July 2025 that includes detached ADUs (DADUs). No owner occupancy is required and no design review is applied.

How big can an ADU be in Bellevue?

The standard maximum floor area is 1,200 sq ft. Up to 300 sq ft used for parking or unheated storage is excluded from the count, an ADU converted from a previously permitted guest cottage is exempt from the cap, and the Director may approve more than 1,200 sq ft where the unit sits entirely on one floor or is added to an existing detached structure. An attached ADU's floor area does not count against the site's single-family floor-area allowance.

What are the setback requirements for an ADU in Bellevue?

An attached ADU follows the main house's setbacks. A new detached ADU follows the middle-housing table in LUC 20.20.538, which is 10 ft front, 15 ft rear and 5 ft side in the SR-1 and SR-2 zones, although a detached ADU may be sited on the lot line that abuts an alley. If you convert an existing structure, today's setback and lot coverage rules do not block the project.

Can I build a DADU in Bellevue?

Yes, but only since 1 July 2025. Detached ADUs were not allowed in Bellevue before Ordinance 6851 (the Middle Housing amendments) took effect. Detached units are limited to 24 ft in height, or 28 ft when built as an addition over an existing accessory structure, and they follow the dimensional table in LUC 20.20.538.

How many ADUs can I build in Bellevue?

Up to two ADUs on a lot where a single-family dwelling is allowed: two attached, one attached plus one detached, or two detached. Note that Ordinance 6931, passed on 28 July 2026, amends the units-per-lot provisions and was still pending codification when this page was written, so confirm the current count with Bellevue before you commit.

Do I have to live in my Bellevue house to rent out the ADU?

No. Bellevue removed its owner-occupancy requirement in 2023 and Washington law bars cities from requiring the owner to live in the ADU or the main house. Rentals of 30 consecutive days or more are allowed; short-term rentals may still be restricted by the city.

Do I need design review for an ADU in Bellevue?

No. Bellevue removed ADU design controls in 2023, and state law bars aesthetic requirements or design review for ADUs that are stricter than those applied to the principal unit.

What does a Bellevue ADU cost in impact fees?

Impact fees for an ADU are capped at 50% of what the same unit would be charged as a principal dwelling under RCW 36.70A.681. That cap is one of the biggest cost differences between Bellevue and California cities, where impact fees often apply in full above a size threshold.

Sources

• Bellevue Land Use Code 20.20.120 — Accessory dwelling units
• Bellevue Land Use Code 20.20.538 — Middle housing dimensional standards
• City of Bellevue — ADU reform (Ordinance 6746, 2023)
• City of Bellevue — Middle Housing code amendments (Ordinance 6851, effective 1 July 2025)
• City of Bellevue — Middle housing building permits
• Washington RCW 36.70A.681 — ADU standards a city may not impose
• Bellevue Planning Commission staff report — middle housing dimensional table (March 2025)