ADULocal ADU Guide

Seattle region / Washington

Seattle ADU rules
& permit guide.

Seattle distinguishes attached ADUs (AADUs) from detached backyard cottages (DADUs). Its current permit guidance ties height, location and unit density to the property’s zoning, so begin with your parcel’s current designation.

Editorial review 2026-09-07 · View sources

The local detail to check first

Before you choose a design

Seattle is updating ADUniverse and its plan gallery after zoning changes. Check the current design and zoning requirements. Sewer treatment capacity charges also belong in the project budget.

Local requirements at a glance

Min/max ADU size

Seattle restricts ADU size and generally counts ADUs toward density. Check the current zone and ADU code rather than using older citywide summaries.

Height

The ADU must comply with the property zone’s current height and location standards.

Parking

Seattle’s current ADU page exempts ADUs from parking requirements.

Process

Attached and detached projects need construction permits. Include King County sewer treatment capacity-charge acknowledgment and any electrical service application.

Your next three steps

  1. Identify the current zone and any environmentally critical area or shoreline conditions.
  2. Choose an attached conversion or detached building and check the current ADUniverse resources.
  3. Prepare the required construction permit documents and sewer-capacity acknowledgment; coordinate electrical service needs.

Washington / Local requirements

Use the rules for your location

Seattle’s current ADU guidance points to its zoning and construction codes. Confirm the applicable zone, unit count and permit path with the city.

Read the current city guidance ↗

A starting point for your design

Local plan resources

ADUniverse design gallery ↗

The city is updating the gallery and guidance. Confirm availability and acceptance of the exact design before hiring its designer.

Questions for your first planning conversation

  • Which approval path applies to my building and ADU type?
  • Do easements, trees, slope, access or fire conditions affect placement?
  • Which utility upgrades and agency reviews should be included in my budget?
  • Are preapproved plans available, and what site work still needs review?