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Zillah City Zoning Code

CHAPTER 17

28 MIDDLE HOUSING AND ACCESSORY DWELLING UNITS

§ 17.28.010 Purpose.

The purpose of this chapter is to implement Engrossed Substitute House Bill 1110 and Engrossed Substitute House Bill 2321, codified in RCW 36.70A.030, RCW 36.70A.635 through 36.70A.638, RCW 36.70A.681, and RCW 36.70A.696, by establishing standards for middle housing and accessory dwelling units within the City of Zillah.
(Ord. 1615, 3/16/2026)

§ 17.28.020 General provisions.

A. 
Nothing in this chapter prohibits detached single-family residences.
B. 
Nothing in this chapter limits the City's authority to require affordable housing as permitted by RCW 36.70A.540.
C. 
Nothing in this chapter requires issuance of a permit where other applicable federal, state, or local requirements are not met.
D. 
Nothing in this chapter modifies the City's obligation to plan for or provide urban governmental services under RCW 36.70A.030.
E. 
No building permit for middle housing shall be approved without compliance with RCW 19.27.097 (adequate water supply).
F. 
Development regulations for middle housing shall not be more restrictive than those applicable to detached single-family residences, except as permitted by state law.
G. 
The same permit and environmental review processes applicable to detached single-family residences shall apply to middle housing unless otherwise required by law.
(Ord. 1615, 3/16/2026)

§ 17.28.030 Definitions.

For purposes of this chapter, the following definitions apply:
Accessory Dwelling Unit (ADU).
A small, self-contained residential unit located on the same lot as a primary dwelling, providing independent living facilities including cooking, sleeping, and sanitation.
Accessory Dwelling Unit – Attached.
An accessory dwelling unit physically attached to the primary dwelling.
Accessory Dwelling Unit – Detached.
An accessory dwelling unit not physically attached to the primary dwelling and which may be attached to an accessory structure such as a garage.
Accessory Dwelling Unit – Interior.
An accessory dwelling unit constructed within the existing building envelope of the primary dwelling.
Administrative Design Review.
A development permit review process conducted by the Planning Director or designee based solely on objective standards, without a public hearing unless otherwise required by law.
All Lots Zoned Predominantly for Residential Use.
Zoning districts in which residential dwellings are the predominant use, excluding zones primarily intended for commercial, industrial, public, or mixed-use development.
Cottage Housing.
Residential units on a lot arranged around common open space, with at least 20% of the lot devoted to common or shared open space.
Courtyard Apartments.
Attached dwelling units arranged on two or three sides of a yard or court.
Development Regulations.
Controls placed on land use or development activities by the City, including zoning, subdivision, critical areas, and shoreline regulations.
Development Standards.
Controls placed on building or site design, including dimensional, parking, and landscaping standards.
Duplex, Triplex, Fourplex, Fiveplex, Sixplex.
Residential buildings containing two, three, four, five, or six attached dwelling units, respectively.
Major Transit Stop.
A stop on a high-capacity transportation system, commuter rail, fixed guideway system, or bus rapid transit route.
Middle Housing.
Residential buildings compatible in scale and character with single-family houses that contain two or more attached, stacked, or clustered dwelling units.
Stacked Flat.
Dwelling units in a residential building of no more than three stories where each floor may be separately rented or owned.
Townhouses.
Buildings containing three or more attached dwelling units extending from foundation to roof with a yard or public way on at least two sides.
Unit Density.
The number of dwelling units allowed on a lot, regardless of lot size.
(Ord. 1615, 3/16/2026)

§ 17.28.040 Applicability.

This chapter applies to all lots zoned predominantly for residential use, except:
A. 
Critical areas and required buffers, except aquifer recharge areas where detached housing is permitted;
B. 
Lots designated as urban separators by countywide planning policies;
C. 
Lots created through the splitting of a single residential lot.
(Ord. 1615, 3/16/2026)

§ 17.28.050 Unit density.

A. 
The minimum permitted density is two dwelling units per lot unless higher density is otherwise allowed.
B. 
Accessory dwelling units do not count toward unit density.
(Ord. 1615, 3/16/2026)

§ 17.28.060 Middle housing types permitted.

The following middle housing types are permitted by right on all lots zoned predominantly for residential use, unless zoning allows higher density:
A. 
Duplexes.
B. 
Triplexes.
C. 
Fourplexes.
D. 
Fiveplexes.
E. 
Sixplexes.
F. 
Townhouses.
G. 
Stacked flats.
H. 
Courtyard apartments.
I. 
Cottage housing.
(Ord. 1615, 3/16/2026)

§ 17.28.070 Dimensional standards.

Dimensional standards for middle housing shall be no more restrictive than those applicable to detached single-family residences and shall comply with RCW 36.70A.635.
(Ord. 1615, 3/16/2026)

§ 17.28.080 Design standards.

Design standards for middle housing shall be objective and reviewed through administrative design review only.
(Ord. 1615, 3/16/2026)

§ 17.28.090 Accessory dwelling units.

A. 
Permitted. Up to two accessory dwelling units are permitted per lot in addition to the principal dwelling.
B. 
Maximum Size. An accessory dwelling unit may not exceed 1,200 square feet.
C. 
Utilities. Separate water and sewer connections shall be required for each accessory dwelling unit. Shared connections are not permitted. These requirements are intended to ensure utility system capacity and protect public health and safety, and shall not be applied in a manner more restrictive than requirements imposed on principal dwelling units.
D. 
Utility Adequacy. Prior to issuance of a building permit, the applicant shall provide written verification from the serving electrical utility demonstrating adequate capacity. This requirement shall not be enforced more restrictively than requirements imposed on principal dwelling units.
E. 
Parking. Parking requirements for accessory dwelling units shall comply with RCW 36.70A.681.
F. 
Owner Occupancy. Nothing in this section requires owner occupancy except as permitted by RCW 36.70A.680.
(Ord. 1615, 3/16/2026)

§ 17.28.100 Parking standards – Middle housing.

Parking standards for middle housing shall comply with RCW 36.70A.635.
(Ord. 1615, 3/16/2026)

§ 17.28.110 Infrastructure standards.

Infrastructure standards for middle housing shall not be more restrictive than those applicable to detached single-family residences.
(Ord. 1615, 3/16/2026)