Seattle City Council passes Accessory Dwelling Units (ADUs) Legislation

On July 1 the Seattle City Council passed a legislation that will make it easier for more property owners to build Detached Accessory Dwelling Units or DADUs and Attached Accessory Dwelling Units or AADUs.

The legislation:

  • Reduces the minimum lot size required to build a DADU on a single-family lot from 4,000 square feet to 3,200 square feet;
  • Increase the maximum size of DADUs from 800 square feet to 1,000 square feet, excluding any parking or storage areas;
  • Removes the owner-occupancy requirement for ADUs;
  • Removes the off-street parking requirement for ADUs;
  • Allows two ADUs on one lot (either one attached and one detached, or two attached) if the second ADU meets a green building standard or will be affordable to households at or below 80% of area median income;
  • Increases the maximum household size permitted on a single-family lot from 8 to 12 unrelated people only if the lot includes two ADUs;
  • Increases DADU height limits by 1-3 feet, with flexibility for green building strategies;
  • Allows design flexibility to preserve existing trees and to convert existing accessory structures to a DADU;
  • Require annual reporting on ADU production and requires that the Office of Planning and Community Development and the Seattle Department of Construction and Inspections conduct a survey of ADU owners and occupants within 3 years.
  • Introduces a Floor Area Limit (FAR) for all new development in single-family zones with some exemptions.
Image courtesy of the Seattle City Council Central Staff

The new Floor Area Limit (FAR) will discourage the tear town of smaller, older homes to build the so-called McMansions.

Graphic courtesy of the Seattle City Council Central Staff

Signed Ordinance 125854 – Council Bill 1219544:  https://seattle.legistar.com/View.ashx?M=F&ID=7532434&GUID=D2A02EE2-1AA9-44BA-AC80-D54045C628E8

Related files: http://seattle.legistar.com/LegislationDetail.aspx?ID=3976805&GUID=6402D8F2-8188-4891-B449-A160356FFD87&Options=ID|Text|&Search=cb+119544