Maximum density and minimum lot size
Seattle Mun. Code § 23.44.060
in effectA. Except as provided in subsection 23.44.060.C, the maximum density is: 1. For stacked dwelling units, one dwelling unit per 600 square feet of lot area; 2. For stacked dwelling units that meet one of the following criteria, one dwelling unit per 500 square feet of lot area: a. Retain a Tier 1 tree, as defined in Section 25.11.130 ; b. Retain two Tier 2 trees, as defined in Section 25.11.130 ; or c. Meet a Green Factor score of 0.6, as measured in Section 23.86.019 ; 3. Within a frequent transit service area, for development consisting entirely of dwelling units in structures that are less than three stories and that are arranged on up to three sides of a common ground-level amenity area equal to at least 20 percent of the lot area that includes usable, contiguous community green space and trees, one dwelling unit per 650 square feet of lot area; 4. For all other dwelling units, one dwelling unit per 1,250 square feet of lot area. B. The minimum lot size for lots created after the effective date of this ordinance is 5,000 square feet. C. Maximum density exceptions 1. A lot that is less than 5,000 square feet may be developed with up to four dwelling units provided that the lot does not contain any riparian corridors; wetlands and their buffers; submerged lands and areas within the shoreline setback; or designated non-disturbance area in steep slopes. 2. A lot that is less than 7,500 square feet and within one-quarter mile walking distance of a stop on a major transit service may be developed with up to six dwelling units if the lot does not contain any riparian corridors; wetlands and their buffers; submerged lands and areas within the shoreline setback; or designated non-disturbance area in steep slopes. 3. A lot that is less than 7,500 square feet and located more than one-quarter mile walking distance from a stop on a major transit service may be developed with up to six dwelling units if the lot meets the following criteria: a. The lot does not contain any riparian corridors; wetlands and their buffers; submerged lands and areas within the shoreline setback; or designated non-disturbance area in steep slopes; b. At least two principal dwelling units are low-income units subject to a regulatory agreement, covenant, or other legal instrument enforceable by The City of Seattle; c. The low-income units are generally distributed throughout the development and have substantially the same functionality as unrestricted units in the development; d. To the extent practicable, the low-income units are comparable to unrestricted units in terms of square footage and number of bedrooms and bathrooms; e. The tenure (i.e., rental or ownership) of low-income units and unrestricted units is the same; f. The regulatory agreement, covenant, or other legal instrument contains criteria and policies to maintain public benefit if the property is demolished or converted to a non-residential use; g. For ownership housing, the low-income units are stewarded by a qualified non-profit organization, which for purposes of this subsection 23.44.060.C.3 means a non-profit organization that the Office of Housing determines as experienced in the development and stewardship of permanently affordable homes, including: 1) Pre-purchase verification of income and other requirements for eligible households, affordable sale price calculations for approval by the Office of Housing, and execution of legal restrictions on the property; and 2) Post-purchase support for homeowners by facilitating resales, monitoring compliance with financial, owner occupancy, and other legal requirements, and clear communication of program guidelines and restrictions; and h. At such times as may be required by the Director of Housing but no less than annually, the property owner (for rental housing) or the qualified non-profit organization (for ownership housing) agrees to file property reports with the Office of Housing, verified upon oath or affirmation, which shall contain such information as the Office of Housing may deem necessary to determine compliance with this subsection 23.44.060.C.3 and the regulatory agreement, covenant, or other legal instrument. 4. For lots that contain any riparian corridors, wetlands and their buffers, submerged lands and areas within the shoreline setback, or designated non-disturbance area in steep slopes, applicants may choose to develop the lot with the number of dwelling units provided in the density limits in subsection 23.44.060.A or with the number of dwelling units calculated as follows: a. Determine the number of units that would be allowed under subsections 23.44.060.C.1 through 23.44.060.C.3 if no environmentally critical areas were located on the lot; b. Determine the percentage of the lot that is not covered by riparian corridors, wetlands and their buffers, submerged lands and areas within the shoreline setback, or designated non-disturbance area in steep slopes; and c. Calculate the number of dwelling units by multiplying the number of units determined in subsection 23.44.060.C.4.a by the percentage of the lot calculated in subsection 23.44.060.C.4.b. At least one dwelling unit is allowed on all lots in existence as of the effective date of this ordinance. 5. Square footage of dwelling units that are Type A units, as defined in the Seattle Building Code, do not count toward maximum density. D. Measurement of minimum lot size and maximum density 1. When calculation of the number of dwelling units allowed results in a fraction of a unit, any fraction over 0.85 constitutes one additional unit. 2. Congregate residence sleeping rooms shall be treated as one-fourth of a dwelling unit for purposes of calculating density. 3. In the case of a development within a unit lot subdivision, the density limit shall be applied to the parent lot as a whole. 4. If dedication of right-of-way is required, permitted density shall be calculated before the dedication is made. 5. When calculating density, the number of dwelling units shall include both accessory dwelling units and principal dwelling units. 6. Areas not counted in calculating the lot size. The following areas shall not be counted in calculating the area of lots for the purpose of calculating the maximum density and the minimum lot size: a. Riparian corridors; b. Wetlands and their buffers; c. Submerged lands and areas within the shoreline setback; and d. Designated non-disturbance area in steep slopes. E. For the purpose of this Section 23.44.060 , designated non-disturbance area in steep slopes shall include all portions of steep slope hazard areas except the following: 1. Areas that are granted relief from the prohibition of development according to Section 25.09.090 ; 2. Areas where development is allowed under a small project waiver according to Section 25.09.090 ; and 3. Areas where intrusion into the steep slope erosion hazard area and buffer is allowed by steep slope erosion hazard area variance according to Section 25.09.290 . (Ord. 127376 , § 31, 2025.)
Source: Seattle Municipal Code (Municode library)URL: https://library.municode.com/wa/seattle/codes/municipal_codeFetched: 7/25/2026