Lynnwood, WA Accessory Structures: ADU Rules (2026)
ADU rules in Lynnwood, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Maximum ADU size
- 1,000 square feet or less
- ADU types recognized
- AADU (attached) and DADU (detached)
- By-right zones
- RN, RM-45, NC, CDM
- State law floor
- HB 1337 (2023) requires 2 ADUs/lot
Summary
Lynnwood defines an accessory dwelling unit (ADU) as 1,000 square feet or less, either attached (AADU) or detached (DADU), under LMC 8.99.0250(A), and permits ADUs by right in the RN, RM-45, NC, and CDM zoning districts per the Title 8 use table.
Accessory Dwelling Unit. A dwelling unit of 1,000 square feet or less located on the same lot as a single-family housing unit, duplex, triplex, townhome, or other housing unit. Often abbreviated as “ADU.” There are two common types of ADUs: a. Attached Accessory Dwelling Unit. An accessory dwelling unit located within or attached to one of the above housing units. Often abbreviated as “AADU.” b. Detached Accessory Dwelling Unit. An accessory dwelling unit that consists partly or entirely of a building that is separate and detached from one of the above housing units and is on the same property. Often abbreviated as “DADU.”
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 3512, passed May 26, 2026).
Full Breakdown
0250(A), Lynnwood defines an accessory dwelling unit as a dwelling unit of 1,000 square feet or less located on the same lot as a single-family house, duplex, triplex, or townhome, splitting the term into an attached accessory dwelling unit (AADU), built into or attached to the main house, and a detached accessory dwelling unit (DADU), a separate building on the same property. 0210 lists ADUs as a permitted ("P") residential use in the residential neighborhood (RN) zone, the RM-45 multifamily zone, the neighborhood commercial (NC) zone, and the CDM zone, and as not permitted in zones like MHP, city center, Alderwood, ACC, PCD, CG, HMU, LI, P-I, and OSP.
Washington State law now sets a floor under this local framework: HB 1337 (2023) requires cities that plan under the Growth Management Act, including Lynnwood, to allow two ADUs on most lots in urban residential zones and bars many of the restrictions cities used to impose, such as owner-occupancy requirements, added parking mandates, and minimum lot sizes tied specifically to ADUs. Any Lynnwood ADU standard that conflicts with that state floor does not control; property owners should confirm current permit requirements with the development and business services department rather than relying solely on the local use table. This is Title 8 Unified Development Code text, not the repealed Title 21 zoning code.
Violations & Fines
Building or occupying an ADU that exceeds the 1,000-square-foot size definition, or placing one in a zoning district where the use table does not permit ADUs, is a Unified Development Code violation. The city can issue a notice of violation and corrective order under LMC Chapter 1.40, with civil penalties starting at $100 the first day and rising to $500 per day until the violation is corrected, and a possible lien on the property for penalties unpaid after 30 days.
Frequently Asked Questions
How large can an accessory dwelling unit be in Lynnwood?
Which Lynnwood zones allow ADUs by right?
Does Washington state law change Lynnwood's ADU rules?
Sources & Official References
Other rules in Lynnwood
How Lynnwood compares: Easiest Cities to Build an ADU·Compare Lynnwood to another location·View the Washington accessory structures overview
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ADU Rules in Nearby Cities
How other cities in Snohomish County handle adu rules.