DADU requirements:

• The minimum lot size required for a DADU is 3,200 square feet in neighborhood residential zones
• A DADU is limited to 1,000 square feet of gross floor area in neighborhood residential zones, including RSL, and 650 square feet in a lowrise zone
• The DADU must meet all the Seattle residential, building, mechanical, electrical, and energy code requirements that apply to single-family dwellings

What is an AADU?
An AADU is a room or set of rooms designed and
established by permit to be a separate dwelling unit.
AADUs can be located in a single-family home in the
Neighborhood Residential (NR) NR3, NR2, and NR1
and Neighborhood Residential Small Lot (RSL) zones.
In the RSL zone they can also be located in a principal dwelling of an apartment unit, carriage or cottage
house, rowhouse, or townhouse. In the lowrise (LR)
zones, AADUs can be located in a single-family home,
rowhouse or townhouse unit

For lots with one accessory dwelling unit (1 AADU or
1 DADU) the total number of residents in both the primary dwelling and the accessory unit cannot exceed
eight people, unless all residents of both units are
related to each other. For NR zoned lots with two
accessory dwelling units (2 AADUs or 1 AADU and 1
DADU), the total number of unrelated residents cannot exceed 12 people