Maximizing Your Home's Value: What Washington's New Housing Laws (HB 1337, 1110, & 5258) Mean for You.

• Maximum Unit Count : You may now create up to two ADUs per property in most residential zones. Attached ADUs (AADUs): AADUs (units inside the main home, like basement apartments) do not count toward your lot's overall 4-6 unit middle housing density limit. Detached ADUs (DADUs): DADUs (separate backyard cottages) do count toward your lot’s overall unit density.

• Income & Investment Potential : The City removed restrictions on ownership, meaning ADUs may now be sold separately from the main house via a Unit Lot Subdivision. This allows you to generate revenue by selling a portion of your lot to a new owner.

• New Size Limit : The maximum size of an ADU has been increased to 1,200 square feet, or 40% of the combined area of the ADU and the primary residence (whichever is larger).

• Parking Requirement : Parking is NOT required for any ADU that is less than 1,000 square feet in floor area. Parking is also NOT required for any ADU if the lot is located within a half-mile of a major transit stop.
• Use Restriction Alert: ADUs are prohibited from being used for short-term rentals (they must be rented for 30 days or longer) and cannot contain a home-based business that requires a Home Occupation Permit.

• Unlock Hidden Equity: Calculate Your Lot's Potential: Bellevue's flexible rules allow two ADUs in addition to the base middle housing units. Find out if your lot is near a major transit stop to qualify for maximum density and parking exemptions.

What It Is: The Clyde Hill Implementation

HB 1110 requires large cities like Bellevue (a Tier 1 City) to allow a broader range of "middle housing" in all areas previously restricted to single-family detached homes. Middle housing includes two or more attached, stacked, or clustered homes compatible in scale with single-family houses.

• Mandated Density: Minimum of four (4) housing units per lot on virtually all residential parcels across the city.

• Maximum Density: Allows up to six (6) units per lot in specified areas.

• Housing Types Allowed: Bellevue allows all nine types of middle housing, including Duplexes, Triplexes, Fourplexes, Sixplexes, Townhouses, and Stacked Flats.

• Parking Requirements: Middle housing projects are exempt from minimum parking requirements when located within one-half mile walking distance of a major transit stop.

• Investment Incentive: Bellevue allows developers building six units to pay a fee in lieu (instead of building affordable units on-site), making it easier to maximize market-rate development.

• Future Density Alert: The rules are now final: Your property can now host a minimum of four units. Find out if you are within a quarter-mile radius of a transit stop, which triggers the potential for up to six units. This density is now a fundamental aspect of your land's investment value.

What It Is: Clyde Hill's Unit Lot Subdivision (ULS)

Unit Lot Subdivision (ULS) is a required process in Bellevue's short plat regulations that allows a single development site (the parent lot) to be legally divided into smaller unit lots. This enables new units—such as duplexes, townhouses, sixplexes, or ADUs—to be sold individually with fee-simple ownership, similar to condominiums.

• Applicability: ULS can be used for any new development that includes attached or detached multifamily dwellings, middle housing, or a primary structure with at least one ADU.

• Flexibility on Zoning: Individual unit lots need not conform to the minimum lot area, minimum density, or dimensional requirements (setbacks, lot width).
• Parent Lot Control: The overall development of the parent lot must meet the existing development and design standards of the underlying land use district.
• Shared Area Liability: Easements, joint use agreements, and maintenance agreements must be executed and recorded for shared common areas (e.g., driveways, parking, landscaping, underground utilities).
• Lot Status: The plat notes state that individual unit lots are not separate buildable sites.