ADU Rulebook

City · Washington

ADU rules in Redmond

4 sources

These are the primary sources for accessory dwelling unit regulations in Redmond: the city's own zoning code, planning department pages, and permit guides. Start here before talking to anyone: the rules below are what your permit reviewer will apply.

Rules at a glance

Detached (backyard) ADU
Allowed

An ADU may be located in a detached structure on the same lot as the primary dwelling unit. Detached ADUs must meet lot coverage and other detached-dwelling standards, but may be sited immediately abutting a lot line that abuts a public alley or right-of-way, overriding other setback regulations.

RZC 21.04.1110.C.2
Attached or internal ADU
Allowed

An ADU may be added to or included within the primary unit. The ADU definition also allows ADUs on lots with a duplex, triplex, townhome, or other middle housing unit, not only single-family homes.

RZC 21.04.1110.C.2.a; RZC 21.78.100 (definition of Accessory Dwelling Unit)
Maximum size
1,000 sq ft (attached or detached); Administrator may allow more if the ADU occupies an entire single floor of the primary dwelling, or on sites over 10,000 sq ft where the ADU is affordable housing or a public benefit is provided; tiny homes capped at 400 sq ft

The 1,000 sq ft cap applies to the total square footage of the ADU. The two enlargement paths are discretionary Administrator approvals, not by-right.

RZC 21.04.1110.C.3
Owner occupancy
Not required

The operative ADU section contains no owner-occupancy requirement; none appears in the version amended by Ord. 3261 either. This is consistent with WA HB 1337 (RCW 36.70A.680), which bars owner-occupancy conditions on non-short-term-rental ADUs.

RZC 21.04.1110 (no owner-occupancy provision in section text)
Extra parking
None: minimum required off-street parking for an accessory dwelling unit is 0 spaces in all three location categories (near frequent transit or TOD focus areas, centers, and all other locations)

Table 21.40.010.D lists 'Accessory dwelling unit ... (0, -)' per dwelling unit in every column, so no off-street parking is required for ADUs anywhere in the city. Older city handouts stating one required space reflect the pre-HB 1337 code.

RZC 21.40.010.D, Table 21.40.010D
Approval process
Permitted use

Accessory dwelling unit is a permitted (P) use in Redmond's residential zones and most mixed-use zones per the Residential Use Table, subject to the standards of RZC 21.04.1110; approval is through a building permit, not a discretionary land use hearing.

RZC 21.04.0100 (Residential Use Table)
Rental restrictions
None specific to ADUs found in the zoning code; no minimum lease term and no ADU short-term-rental provision

RZC 21.04.1110 contains no rental or occupancy-term rules, and an exact-phrase search of the hosted Redmond Municipal Code and Zoning Code for 'short-term rental' returned no matches.

RZC 21.04.1110 (absence of rental provisions); code search on redmond.municipal.codes
The fine print: 7 caveats that can change the picture
  • Two ADUs or tiny homes are allowed on each residential lot (RZC 21.04.1110.C.1), reflecting HB 1337 compliance.
  • The 1,000 sq ft size cap can be exceeded only through discretionary Administrator approval (full-floor internal ADUs, or sites over 10,000 sq ft with an affordability or public-benefit showing).
  • Detached ADUs must meet lot coverage and other detached-dwelling standards of the zone, except they may abut a lot line along a public alley or right-of-way.
  • Detached ADUs require fire sprinklers per the city's Residential Permits page.
  • ADUs are allowed on lots with middle housing (duplex, triplex, townhome) as well as single-family homes, per the RZC 21.78.100 definition.
  • Ordinance 3261 (adopted 6/2/2026, effective 6/13/2026, pending codification as of 7/19/2026) amends RZC 21.04.1110, but the only change is deleting the old subsection barring ADUs from counting toward affordable housing requirements; the substantive ADU standards are unchanged.
  • ADUs cannot be used to satisfy affordable housing requirements under RZC Chapter 21.20 in the currently codified text (this subsection is struck by Ord. 3261).

Summarized from Redmond's ordinance text, read July 2026; every row links the code section it came from. Rules often vary by zone and lot, so treat this as orientation, not a permit determination, and confirm with the planning department before you commit to a design.

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ADU regulations

Washington statewide law also applies

Washington sets baseline ADU rights at the state level. Where local rules are stricter than state law allows, state law usually wins, so both are worth reading.

See Washington statewide rules

Spotted something outdated?

Zoning codes change. If a link is dead or Redmond has updated its ordinance, report it and we'll verify against the official source.

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