Yes. Since July 1, 2025 (Ordinance 6851, implementing Washington HB 1337) every Bellevue lot that allows a single-family house may add up to two accessory dwelling units, attached or detached, under Land Use Code 20.20.120. A detached ADU (DADU) may be up to 1,200 sq ft and 24 ft tall (28 ft when built over an existing garage), needs no parking if it is under 1,000 sq ft or within half a mile of a major transit stop, and the owner does not have to live on the property. The permit is a standard one- and two-family (BS) building permit filed on MyBuildingPermit.com, with plan-review and inspection billed by the hour against deposits; transportation impact fees on an ADU are capped at half the single-family rate ($8,185 in 2026), and most of the city pays no school impact fee. ADUs may be sold separately as condominiums. The city's pre-approved DADU plan program is still being designed (council study session March 10, 2026) and no plans are available yet.
In Bellevue you will also hear an ADU called a DADU — short for detached accessory dwelling unit, the usual term across Washington. The rules on this page apply either way.
Zoning & Size Requirements [1][2][3][4][5][6][7][8][9]
Yes — Bellevue allows ADUs. A detached ADU can typically be up to 1,200 sq ft under current Washington and Bellevue zoning rules.
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| Allowed Zones | Any lot in a land use district that allows a single-family dwelling, i.e. every residential district LL-1 through MDR-2 (LUC 20.20.120.C.1 as rewritten by Ord. 6851, effective July 1, 2025). Detached ADUs were not allowed before that date; the 2023 ADU Reform (Ord. 6746) covered attached units only. State floor: RCW 36.70A.681(1)(c)-(d) |
| Max Size (Detached) | 1,200 sq ft of floor area (LUC 20.20.120; confirmed on the City's 2026 Pre-Approved Plans page). The Director may approve a larger unit when it is an addition to, or a conversion of, an existing detached accessory structure; a converted guest cottage is exempt from the cap if not enlarged. The council draft also excluded up to 250 sq ft of garage or unheated storage per ADU - confirm that clause with Land Use Review |
| Max Size (Attached) | 1,200 sq ft of floor area (LUC 20.20.120.C.3). The Director may approve more when the ADU sits entirely on one floor of the main house. The 2023 formula of '1,200 sq ft or 40% of the structure, whichever is larger' (Ord. 6746) was replaced by the flat cap with Director exceptions in the 2025 rewrite. Attached ADUs follow the main house's height and setbacks |
| Max Size (JADU) | Washington has no junior ADU category. A small unit carved out of the house is simply an attached ADU and counts as one of the two ADUs allowed per lot (LUC 20.20.120) |
| Max Height | Detached ADU: 24 ft measured to the highest point of the structure, or 28 ft when built as an addition over an existing or proposed accessory structure such as a garage (LUC 20.20.120.D.1; City Pre-Approved Plans page, 2026). Attached ADUs use the main house's height limit. State floor: a city may not cap ADU roof height below 24 ft (RCW 36.70A.681(1)(g)) |
| Max Units | 2 ADUs per lot in any combination - two attached, two detached (one or two buildings), or one of each - in addition to the main house (LUC 20.20.120.C.1; RCW 36.70A.681(1)(c)). ADUs may be sold separately as condominiums (Ord. 6746, 2023; RCW 36.70A.681(1)(k)). Under the HB 1110 middle-housing rules in LUC 20.20.538 a lot may instead hold up to 4 units (6 within 1/2 mile of a major transit stop or with 2 affordable units), and ADUs can be used to reach that count |
Setback Requirements [1][2][3][4][5][6][7][8][9]
Bellevue requires a rear setback of about 10 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | Detached ADUs use the middle-housing setbacks in LUC 20.20.538 Table C.1, which the council draft set at 10 ft in SR-3 through MDR-2 and 15 ft in LL-1, LL-2, SR-1 and SR-2; a DADU may sit on a rear lot line that abuts a public alley (LUC 20.20.120.D.2; RCW 36.70A.681(1)(i)). Attached ADUs use the main house's rear setback. Confirm the adopted table with Land Use Review, 425-452-4188 |
| Side Setback | Detached ADUs: 5 ft in every residential district under the middle-housing table in LUC 20.20.538 Table C.1 (council draft; adopted table not re-read, code host blocked). Attached ADUs use the main house's side setback. By state law an ADU setback may not be more restrictive than the main house's (RCW 36.70A.681(1)(h)) |
| Front Setback | Detached ADUs: the middle-housing front setback in LUC 20.20.538 Table C.1 - 10 ft in SR-1 through MDR-2, 20 ft in LL-2 and 25 ft in LL-1 per the council draft; an existing garage may be converted to an ADU even if it violates today's setbacks or lot coverage (LUC 20.20.120.C.4; RCW 36.70A.681(1)(j)). Confirm the adopted figures with Land Use Review |
| Parking Required | None for an ADU under 1,000 sq ft (garage area excluded) or within 1/2 mile of a major transit stop; 1 space for 1,000-2,000 sq ft; over 2,000 sq ft, 1 space on lots under 6,000 sq ft and 2 on larger lots, in addition to the main house's spaces (LUC 20.20.120.C.5; City ADU Reform page; RCW 36.70A.681(2)) |
| Owner Occupancy | Not required. Bellevue removed its owner-occupancy rule with Ord. 6746 on July 17, 2023 (City ADU Reform page), and RCW 36.70A.681(1)(b) now forbids any such requirement statewide |
| Min Lot Size | No ADU-specific minimum: any lot that meets the minimum lot size for its main house may add ADUs (RCW 36.70A.681(1)(e); LUC 20.20.120.C.1). On lots of 2,000 sq ft or less the city may still cap the number at two ADUs plus the main house (RCW 36.70A.681(3)) |
Permit Process & Fees [10][11][12][13][14][15]
An ADU permit in Bellevue goes through a ministerial, by-right review. The City publishes no target review time for a BS permit; plan review is billed hourly against a submittal deposit, so timing follows the review queue. Ask Permit Processing (425-452-6800) for the current first-review estimate. Permit fees: Fees are set by the 2026 fee ordinance (Ord. 6879): a plan-review deposit at submittal and an inspection deposit at issuance, charged at the stated hourly rate with monthly invoices for overage. Use the City's Permit Fee Estimator (permitfeeestimator.bellevuewa.gov) for a figure.
| Approval Process | By-right building permit: a one- and two-family residence (BS) permit for each building, filed online at MyBuildingPermit.com with PDF plans (City 'Middle Housing Building' permit guide). A separate Clearing and Grading (GD) site permit is required when the project has more than one building with dwelling units. No land-use review, ADU registration or neighbour notice applies (removed by Ord. 6746, 2023). Structures with 3-6 units use the Middle Housing (MH) permit instead |
| Review Timeline | The City publishes no target review time for a BS permit; plan review is billed hourly against a submittal deposit, so timing follows the review queue. Ask Permit Processing (425-452-6800) for the current first-review estimate |
| Permit Fees | Fees are set by the 2026 fee ordinance (Ord. 6879): a plan-review deposit at submittal and an inspection deposit at issuance, charged at the stated hourly rate with monthly invoices for overage. Use the City's Permit Fee Estimator (permitfeeestimator.bellevuewa.gov) for a figure |
| Impact Fees | Transportation impact fee: single-family rate $8,185 per dwelling from Jan. 1, 2026 ($8,430 from Jan. 1, 2027, Ord. 6888); state law caps an ADU at 50% of the principal unit's fee (RCW 36.70A.681(1)(a)), so expect about $4,092 at most - the 2026 schedule has no ADU line, confirm the category with Transportation Development Review (425-452-4236). School impact fee: only in the Issaquah ($4,728 per single-family unit) and Renton ($1,003) school district parts of the city, and an ADU pays 50% (BCC 22.18.100, Ord. 6852); no school impact fee in the Bellevue School District. ADUs are exempt from street frontage improvements (BCC 14.60.110.G). Water and sewer connection charges apply separately - see Utilities Permit Fees |
| Plan Check | Standard building plan review by Development Services under the BS permit; reviewers charge hours against the deposit, and the middle-housing amendments removed design-review and design-matching controls for ADUs (Ord. 6746; RCW 36.70A.681(1)(h)). A pre-application meeting is optional |
| Pre-Approved Plans | None available yet. The council made a DADU and cottage pre-approved plans program a 2024-2026 priority; the March 10, 2026 study session laid out a three-phase program ending with up to 10 city-pre-approved plans sold at a set price, timed to the next state building code adoption (City Pre-Approved Plans page) |
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Construction Costs [16][17][18][19]
Building an ADU in Bellevue typically costs $325,000-$550,000 ($400-$650 per sq ft); a garage conversion runs $100,000-$225,000.
See what this means for your lot — ask Bellevue ADU builders for a quote →
| Average Build Cost | $325,000-$550,000 |
| Cost per Sq Ft | $400-$650 |
| Garage Conversion | $100,000-$225,000 |
| Prefab ADU (Installed) | $300,000-$450,000 |
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Rental Income Potential [20][21]
A 2-bedroom ADU in Bellevue rents for around $2,900-$3,750/mo, an estimated 5-8% gross rental yield on a $400,000-$550,000 detached build renting at $2,700-$3,500/mo, before vacancy, taxes and financing; conversions of existing space at $100,000-$225,000 yield roughly twice that.
| Avg Rent (1 Bedroom) | $2,500-$3,200/mo |
| Avg Rent (2 Bedroom) | $2,900-$3,750/mo |
| Short-Term Rental | No citywide ban identified. Stays under 30 days are regulated as 'short term stay uses' under LUC 20.20.800, which Ord. |
| Est. Annual ROI | 5-8% gross rental yield on a $400,000-$550,000 detached build renting at $2,700-$3,500/mo, before vacancy, taxes and financing; conversions of existing space at $100,000-$225,000 yield roughly twice that |
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Recent Law Changes
What's Changed Recently
- June 11, 2026: Washington EHB 1345 (Chapter 231, Laws of 2026) took effect. It lets counties allow detached ADUs outside urban growth areas and amends RCW 36.70A.696; it does not change the rules inside Bellevue, which lies entirely within the urban growth area
- March 10, 2026: City Council study session on a DADU and cottage-housing pre-approved plans program (three phases, up to 10 city-reviewed plans for purchase); no plans are available yet
- January 1, 2026: Ordinance 6888 set the transportation impact fee at $8,185 per single-family dwelling, rising 3% each January; an ADU pays at most 50% of the principal unit's fee under RCW 36.70A.681(1)(a)
- July 1, 2025: Ordinance 6851 (adopted June 24, 2025) rewrote LUC 20.20.120 to implement HB 1337 and HB 1110: detached ADUs legal for the first time, up to two ADUs on every lot that allows a single-family house, 1,200 sq ft cap with Director exceptions, DADU height 24 ft (28 ft over an existing accessory structure), setbacks per the new middle-housing section LUC 20.20.538, DADUs allowed on an alley lot line, garage conversions allowed regardless of setbacks
- June 24, 2025: Companion Ordinance 6852 amended the City Code so an ADU pays 50% of the school impact fee (BCC 22.18.100), is exempt from street frontage improvements (BCC 14.60.110.G) and is treated as residential, not commercial, development
- July 17, 2023: Ordinance 6746 (ADU Reform) removed owner-occupancy, the ban on selling an ADU as a condominium, design-matching controls and the ADU registration and notice steps, and raised the attached-ADU cap from 800 sq ft to 1,200 sq ft. It did not legalize detached ADUs
Tips for Building an ADU in Bellevue
- Detached ADUs have only been legal in Bellevue since July 1, 2025, so most online guides and older city handouts describe the attached-only rules; work from LUC 20.20.120 as amended by Ordinance 6851
- Keep a DADU under 1,000 sq ft, or build within half a mile of a major transit stop, and no parking space is required; between 1,000 and 2,000 sq ft you need one space in addition to the house's
- Converting an existing garage is the cheapest route and the code lets you keep it where it stands even if it breaks today's setbacks or lot coverage (LUC 20.20.120.C.4; RCW 36.70A.681(1)(j))
- Check which school district your parcel is in: lots served by the Issaquah or Renton school districts pay a school impact fee (halved for an ADU); the Bellevue School District portion of the city pays none
- An ADU can be sold separately as a condominium under both Bellevue code and RCW 36.70A.681(1)(k); talk to a real-estate attorney about the condominium declaration before designing
- Cost basis: build costs are Seattle-metro industry guides published November 2025 to May 2026 ($400-$650 per sq ft all-in for new detached construction); no Bellevue-specific published cost survey was found. Rents are HUD FY2026 small-area fair market rents for Bellevue ZIP codes 98004-98008 (1BR $2,510-$3,220, 2BR $2,930-$3,750)
- Cost basis (2026-09-20 re-verification): short term allowed: No citywide ban identified. Stays under 30 days are regulated as 'short term stay uses' under LUC 20.20.800, which Ord. 6851 amended in 2025; the section could not be re-read for this update, so confirm current limits with Land Use Review (425-452-4188) before listing an ADU nightly
ADU Builders in Bellevue
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Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- LUC 20.20.120 Accessory dwelling units - Bellevue Land Use Code (as amended by Ord. 6851) Municipal Code — Accessed 2026-09-20
- LUC 20.20.538 Middle housing - Bellevue Land Use Code (dimensional table for DADU setbacks) Municipal Code — Accessed 2026-09-20
- Ordinance No. 6851 - enactment record (adopted 6/24/2025, effective 7/1/2025, codified) Municipal Code — Accessed 2026-09-20
- Middle Housing LUCA - Planning Commission staff report and strikedraft, March 20-21, 2025 (proposed LUC 20.20.120 and 20.20.538) - City of Bellevue government — Accessed 2026-09-20
- Pre-Approved Plans (DADU size 1,200 sq ft, height 24/28 ft; program status) - City of Bellevue government — Accessed 2026-09-20
- Accessory Dwelling Unit (ADU) Reform LUCA, Ordinance 6746 - City of Bellevue government — Accessed 2026-09-20
- Middle Housing Code Amendments (Ordinances 6851 and 6852, June 24, 2025) - City of Bellevue government — Accessed 2026-09-20
- RCW 36.70A.681 Accessory dwelling units - Limitations on local regulation (HB 1337) state_statute — Accessed 2026-09-20
- EHB 1345, Chapter 231, Laws of 2026 - detached ADUs outside urban growth areas (effective June 11, 2026) state_statute — Accessed 2026-09-20
- Middle Housing Building permit guide (BS, MH and GD permit types) - City of Bellevue Development Services government — Accessed 2026-09-20
- Permit Fees and Payment (2026 fee ordinance, deposits, hourly billing, fee estimator) - City of Bellevue government — Accessed 2026-09-20
- Transportation Impact Fee Rates effective 01/01/2026 (Ord. 6888) - City of Bellevue government — Accessed 2026-09-20
- Transportation Impact Fees - City of Bellevue Transportation government — Accessed 2026-09-20
- Ordinance No. 6852 (school impact fee 50% for ADUs, BCC 22.18.100; street frontage exemption, BCC 14.60.110.G) - City of Bellevue Municipal Code — Accessed 2026-09-20
- Pre-Approved Plans program status - City of Bellevue government — Accessed 2026-09-20
- Cost to Build a DADU in Seattle (2025-2026 Update) | Ballard Backyard Cottages industry — Accessed 2026-09-19
- How Much Does It Cost to Build an ADU in Seattle? 2026 Guide (Jan. 8, 2026) | Kolmo industry — Accessed 2026-09-19
- Seattle ADU Cost 2026 by Type and Size (updated May 12, 2026) | ADU Glossary industry — Accessed 2026-09-19
- Prefab ADU 2026: Brands, True Costs (updated May 19, 2026) | OwnADU industry — Accessed 2026-09-19
- FY 2026 Small Area Fair Market Rents, Seattle-Bellevue HUD Metro FMR Area, ZIPs 98004-98008 | HUD User Government Data — Accessed 2026-09-20
- Ordinance No. 6851 enactment record (amends LUC 20.20.800 Short term stay uses) Municipal Code — Accessed 2026-09-20
Frequently Asked Questions
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