Below is a brief reference to some of the middle housing and accessory dwelling unit regulations in Des Moines. Prior to submitting a permit application, please refer to the full set of middle housing and accessory dwelling unit regulations in Title 18 Des Moines Municipal Code (DMMC) and DMMC 18.55.140.
Middle Housing
Middle housing is defined as buildings that are compatible in scale, form, and character with single-family houses and contain two or more dwelling units. The purpose of middle housing is to create more homes for Washington by increasing housing capacity and allowing various middle housing types in residential zoning districts where they were not previously allowed.
Middle Housing Types
Des Moines accommodates the following types of Middle Housing:
• Duplex
• Triplex
• Fourplex
• Townhome
• Stacked Flats
• Cottage Housing
Accessory Dwelling Units
An accessory dwelling unit (ADU) is a dwelling unit located on the same lot as a single-family housing unit, duplex, triplex, townhome, or other middle housing unit. ADUs provide complete independent living facilities exclusive for one or more persons and include provisions for living, sleeping, eating, cooking, and sanitation.
ADU Types
An ADU can be a detached structure or an attached part of a structure that is subordinate and incidental to the main or primary dwelling unit. Tiny homes on wheels, RVs, storage structures, and mobile homes are NOT considered ADUs.
Permitted Zones
Middle Housing and ADUs are permitted in the following zones:
P = Permitted
*SFR = Single Family Residential Zones include RS-15,000; RS-9,600; RS-8,400; RS-7,200; and RS-4,000
*53 = DMMC 18.52.010A Middle Housing Footnote 53
*52 = DMMC 18.52.010A Accessory Dwelling Unit Footnote 52
Density
The City allows up to 4 units per lot or 24 units per acre (whichever is greater) as calculated on a site-by-site basis. Primary and accessory dwelling units count toward that 4 unit maximum and a maximum of 3 ADUs are permitted per lot. Example: If four units is the maximum total number of units allowed on a given lot and a triplex has been developed, one ADU may be added to the lot.
Development Standards
Middle housing and accessory dwelling units are subject to the standards of the underlying zone in which the property is located for required height, lot coverage, setbacks, etc. For a comprehensive list of middle housing and ADU development standards, see chapter 18.57 DMMC and DMMC 18.55.140.
Required Permits
A building permit is required for new construction, conversions, additions, alterations, or to legalize an unpermitted ADU or middle housing unit. Depending on the scope of work, your project may also require electrical, plumbing and/or mechanical permits or critical area review. Contact the Building Department at [email protected] or information on applications and fees.
Apply online here: https://desmoines-wa.permittrax.com/Citizen/Home
Frequently Asked Questions
Why are there new middle housing and ADU regulations?
State law required all local governments in Washington State planning under the Growth Management Act to update their regulations to comply with House Bill 1110 and House Bill 1337 by June 30, 2025.
What is my property zoned?
Visit the City’s GIS Mapping Tool to look up property zones.
What are the permitting fees for middle housing and ADUs?
Refer to the adopted Planning and Engineering Fee Schedule.
Can I have middle housing and an ADU on my property?
Middle housing Ordinance No. 1821 includes the potential for up to four dwelling units (one single-family residence, up to four middle housing units, and/or up to three ADUs = maximum of four). Note that any development will need to meet the development regulations for the underlying zone, and parking and environmentally critical areas may affect what may be developed on a particular lot.
Can I rent a primary dwelling unit, middle housing unit, and ADU at the same time?
Yes! The City no longer requires owner occupancy. Chapter 5.04 DMMC requires all persons wishing to conduct any business within the City to first secure a business license. If a unit is to be a rental, the property owner shall also apply for and obtain a City of Des Moines business license prior to renting out the unit. Information/applications may be found here.
Can I convert my shed or garage to an ADU?
An ADU may be converted from legal and legal nonconforming structures existing on the effective date of Ordinance No. 1820, including but not limited to detached garages, even if they violate current code requirements for setbacks and lot coverage for the underlying zone.
Can I sell/turn my ADU into a condo?
An ADU may be sold or otherwise conveyed separately as a condominium unit independently from the primary unit.
Does the City offer pre-approved ADUs?
The City does not currently offer pre-approved ADU templates.
How do I legalize an unpermitted ADU?
To legalize an unpermitted ADU, the owner would need to submit a building permit to the city for review and approval. The ADU would need to comply with development standards for the underlying zone.
Have More Questions?
We’re here to help! Contact the Planning Division at [email protected] or visit the Community Development Office during counter hours held Tuesday, Wednesday, and Thursday from 9am - 4pm at 21630 11th Ave S, Suite D, Des Moines, WA 98198.