Shoreline, WA Zoning Overlays & Bonuses: Density Bonus Law (2026)

Shoreline built a density bonus into its middle-housing rules to reward keeping existing homes rather than tearing them down. Footnote (23) to Tables 20.50.020(1) and (2) in SMC § 20.50.020, titled 'Flexibility for Unit Conversion and Retention of Existing Structures,' lets density and bulk standards be modified when an existing dwelling unit is retained on site or converted to a middle housing type, provided the retained structure keeps at least 50 percent of the building's footprint, 100 percent of its front, street-facing facade excluding garages, and 50 percent of its exterior walls.

Once those retention thresholds are met, footnote (23)(a), the 'Density Bonus,' exempts one existing dwelling unit per lot from the zone's unit density maximum, on top of whatever new units the property would otherwise be allowed to add. The same footnote pairs the density bonus with two other modifications: (23)(b) allows up to 10 percent additional hardscape if needed for a required shared driveway, and (23)(c) lets a legally nonconforming structure's existing setbacks and height carry over into any addition needed to convert the retained unit to middle housing.

This retention-based density bonus is separate from the transit-proximity density increase in footnote (22), which raises the residential unit maximum within one-half mile of a major transit stop, and from the Deep Green Incentive Program height bonus referenced elsewhere in SMC § 20.50.020. Planning and Community Development verifies retention compliance and footprint/facade/wall-percentage calculations during permit review before granting the exempted unit count under footnote (23)(a).