This page provides guidance, model ordinances and other resources to assist local jurisdictions in developing middle housing regulations for their communities.
Middle housing is a range of housing types, from duplexes to sixplexes, townhomes, courtyard apartments and cottage housing, intended to be compatible with single-family neighborhoods. The tools provided here are intended to support communities required to include middle housing development options; however, these tools or ideas from these tools may be used by any community looking to include more housing options in their community.
Additionally, accessory dwelling units (ADUs) are required to be provided in every GMA (Growth Management Act) community. While many jurisdictions have adopted ADU regulations, the 2023 legislature provided parameters for how ADUs are regulated, including removing some barriers to development, such as size limitations. The tools provided here guide jurisdictions.
Middle housing guidance
Middle housing is intended to be compatible with single-family neighborhoods while providing more dwelling units per lot. It supports housing affordability and increases housing stock while generally utilizing existing infrastructure. The following documents are intended to guide local jurisdictions in implementing their own middle housing legislation.
- Middle housing update deadlines (PDF)
- Middle housing quick guide (PDF)
- Middle housing checklist (Word)
- Middle housing permit checklist for pre-empted jurisdictions (Word)
- Rural middle housing fact sheet (PDF) – Middle housing outside of urban growth areas requires specific considerations. This guide supports rural communities’ placement of middle housing where adequate public facilities are available.
Model Ordinances
- User Guide for Middle Housing Model Ordinances (PDF)
- Model Ordinance for cities 25,000 and over (PDF)
- Model Ordinance for cities under 25,000 (PDF)
For communities seeking a time extension or the use of the substantially similar alternative or a certification of an empirical parking study, please use the corresponding process outlined in WAC 365-199, specifically:
- WAC 365-199-060 Approval of substantially similar alternative action
- WAC 365-199-070 Extension for certain areas at risk of displacement
- WAC 365-199-080 Extension for certain areas due to lack of infrastructure capacity
- WAC 365-199-090 Certification of empirical parking study
Resources
Commerce strives to support your work through providing valuable resources, tools and examples. Please contact us if you need any of the following in an editable format.
Several preemption clauses related to housing development were enacted in the 2023-24 legislative sessions. Refer to the preemptive state laws for infill housing fact sheet (PDF) for detailed information.
Washington state leads the nation in taking bold action to reform parking regulations. Commerce has developed guidance to support counties, cities and towns in implementing state laws concerning parking regulation, including the Parking Reform and Modernization Act.
- Guidance for Implementing State Parking Requirements (PDF)
- Guidance for Parking Management (PDF)
- Draft parking guidance webinar, May 2026 (Vimeo)
- Parking Reform and Modernization (PRMA) Act fact sheet (PDF)
- PRMA template slide deck (PPT)
Empirical parking study guidance
Both Middle Housing and accessory dwelling unit requirements include options for developing an empirical parking study to determine appropriate parking requirements (outside of the requirements of state statute). The following documents provide guidance to local governments in developing an Empirical Parking Study and in making a certification request to Commerce.
- Empirical parking study guidance (PDF)
- Empirical parking study application checklist (PDF)
- Empirical parking study presentation slides (PPT)
- Empirical parking study presentation video recording (Vimeo)
Parking study certification requests
RCW 36.70A.535 requires cities and counties planning under the Growth Management Act to adopt development regulations allowing co-living as a permitted use on any lot located within an urban growth area that allows at least six multifamily residential units, including on a lot zoned for mixed-use development.
This co-living guidance is intended to support planners, advisory bodies, elected officials and interested parties in implementing code amendments related to RCW 36.70A.535. This guidance uses diagrams, references to public informational documents, and real-world examples to offer recommendations and best practices for the development of co-living housing.
- Co-living guidance (PDF)
- Co-living model ordinance (Word)
- Co-living checklist (Word)
- Co-living parking study guidance (PDF)
- Co-living parking study factsheet (PDF)
- Co-living parking evaluation checklist (PDF)
The following sample of co-living code was developed for a specific region and contains recommendations beyond those required by RCW 36.70A.535. However, it includes a range of recommendations on various co-living options, addressing many common questions and may provide a helpful tool. Jurisdictions should consider local conditions and needs when developing code.
Residential Lot Splitting
In 2025, House Bill 1096 defined lot splitting and outlined the process in RCW 58.17.145. The law includes new requirements that cities must adopt by July 27, 2027 unless their periodic update is due in 2027. Commerce developed a fact sheet to support city planners adopting the new requirements.
Unit Lot Subdivision
In 2023, Washington state law changed to require unit lot subdivisions be included in short plat regulations for all cities, towns, and counties to be adopted before or with their next periodic update of comprehensive plans and development regulations. See RCW 36.70A.130 and Commerce’s periodic update page for more information on deadlines.
A unit lot subdivision (ULS) creates new lots much like a typical subdivision, except a ULS allows flexible application of dimensional standards. In a ULS, the development as a whole is on the “parent lot” which conforms to the zoning dimensional standards while individual “unit lots” are not required to. Unit lots (also called child lots) are individual, sellable, legal lots of record with their own tax or parcel identification number.
Neighborhood infill
Neighborhood infill development guidance addresses potential barriers to the development of neighborhood infill housing, provides examples of proactive solutions, and provides resources for planners to lead discussions with service providers.
Neighborhood commercial
The Neighborhood Commercial Fact Sheet was developed at the request of cities, to encourage commercial opportunities compatible with neighborhoods. Permitting neighborhood commercial goes hand-in-hand with increased allowances for residential density. Additionally, it can help facilitate infrastructure improvements.
Building conversions
Conversion of existing buildings to residential uses creates new opportunities for infill housing in big and small cities. Cities in Washington must allow additional new housing units in existing buildings consistent with state law. This fact sheet provides an overview of the statutory requirements for local government regulation of building conversions.
Ground-floor commercial
To encourage more residential options, state law limit a city’s ability to require development of ground floor commercial in certain areas. This guide summarizes the law.
Manufactured homes
Manufactured/mobile home communities (MHCs) are residential areas that house multiple manufactured or mobile homes with shared infrastructure and amenities.
As communities across the state plan for housing that meets the needs of all income segments, they should take a careful look at this naturally occurring source of affordable housing.
Commerce prepared these guides to help local governments consider preserving this housing type.
- Manufactured and other non-traditional housing types (PDF)
- Manufactured/mobile home community preservation for local governments (PDF)
Alternative ownership
Shared equity homeownership models (SEHM) have the potential to meet housing needs for low- and moderate-income households by providing an alternative to traditional homeownership and renting.
These models provide permanently affordable housing and equity-building homeownership opportunities through the use of deed restrictions that limit sales to low- and moderate- income households.
Commerce prepared this fact sheet to help local governments understand how they can support these options.
- General Middle Housing FAQ (PDF)
- Jurisdictions subject to Chapter 332, Laws of 2023 (PDF)
- Middle Housing Building Types (PDF)
- Middle Housing Lot and Block Models (PDF)
- Middle Housing – Introduction (PPT)
- Middle Housing Study (PPT)
- Middle Housing – What, How and Where? (PPT)
- Middle Housing – How Do We Get More? (PPT)
- Middle Housing Summary of Resources (PPT)
- Middle Housing Presentation Videos
- Middle Housing appraiser engagement FAQ (PDF)