This page provides an overview of infill development for local governments in Washington State, including information on infill development options, examples of plans and ordinances, relevant statutes, and recommended resources.
Infill development is the process of developing vacant or under-utilized parcels within existing urban areas that are already largely developed. Most communities have significant vacant land within their city limits, which, for various reasons, has been passed over in the normal course of urbanization. Communities across the country are increasingly recognizing that the spread-out patterns of growth, which have shaped American communities for the past several decades, cannot be sustained. This combined with the reduced land supply has created new interest in infill development opportunities in central and suburban cities alike.
Successful infill development can increase residential densities to support improved transportation and a wider variety of neighborhood amenities. Infill projects can help to increase the variety of housing types available by promoting small to medium scale housing. This scale of housing, ranging from duplexes to mid-rise apartments, is sometimes referred to as Missing Middle Housing because it is often overlooked in favor of single-family home or high-rise development. Jurisdictions employ a variety of strategies to promote infill development, including addressing barriers to developing on small urban lots, creating infill incentive programs and allowing for a greater variety of housing types. These strategies are often paired with design guidelines to ensure that new infill development matches or enhances the physical character of the community.
More and more communities in Washington are analyzing the capacity of potential infill sites to both accommodate new growth and serve as an alternative to sprawl development.
Infill development may be very small in scale such as a single-family house on a vacant lot within a developed block. It can also occur on a much larger scale such as an entire block or even the redevelopment of hundreds of acres (as in the case of the redevelopment of Denver’s former Stapleton Airport site into the 4,700-acre, mixed-use community of Stapleton). Different types of infill development may be appropriate in different areas depending on the surrounding context and a community's goals for future growth.
The following is a list of different infill development options, focusing primarily on small- to medium-scale infill projects, with more information on each type on the sections below:
- Residential Development – Provides development options that increase the amount of residential housing options as well as make them potentially more affordable
- Small-Lot Development – Small-lot infill development is encouraged by designating zones that relax development regulations like minimum lots size and setback requirements.
- Mixed Use Development – A complementary mix of uses in close proximity such as residential, retail, commercial, employment, civic and entertainment uses - sometimes in the same building.
- Transit-Oriented Development (TOD) – TOD is an effort to focus residential construction in areas with convenient access to transit options, promoting walkability and use of transit.
- Brownfield Redevelopment – A brownfield is an abandoned, idled, or underused property where expansion or redevelopment is complicated by the presence or potential presence of contamination.
- Greyfield Redevelopment – A greyfield refers to an old, abandoned, or underutilized property used for retail or commercial shopping such as a mall. These properties typically do not involve environmental concerns but can demand the replacement or improvement of old infrastructure.
Infill development serves as a useful way to increase the amount of residential housing options as well as make them potentially more affordable. This can involve adding onto properties that have existing structures on them or building multifamily units on undeveloped land. In either case, diversifying the housing stock with ADUs and missing middle housing options can also address the goals and purpose of transit-orientated and small-lot developments.
Accessory Dwelling Units (ADUs)
An ADU is a small, self-contained residential unit located on the same lot as an existing single-family home. It has all the basic facilities needed for day-to-day living independent of the main home, such as a kitchen, sleeping area, and a bathroom. As the term "accessory" implies, ADUs are generally defined to be smaller in size and prominence than the main residence on the lot. An ADU may be created as a separate unit within an existing home (such as in an attic or basement), an addition to the home (such as a separate apartment unit with separate entrance), or in a separate structure on the lot (such as a converted garage).
For more information, see our page on Accessory Dwelling Units.
Missing Middle Housing
Missing Middle Housing refers to homes that are on the building spectrum between single-family homes and high-density apartment buildings.
For more information, see our page on Missing Middle Housing.
Live-work spaces contain one or more dwelling units attached or detached from a non-residential space. The flexible non-residential or workspace may have a taller height and a shopfront frontage. Live-work options are great solutions for connecting jobs and housing for improving density and facilitating economic activity. As more people decide to permanently work from home, live-work buildings could prove to be a growing investment option.
For more information, see the section in our Missing Middle Housing page on Live-Work Builidings.
A number of communities have established some small lot zones with reduced minimum lot size requirements, which tend to reduce the cost of land associated with each residence and allow developments with more units per acre. Other local codes provide for attached housing, corner lot duplexes, cottage or clustered housing, or other more flexible arrangements that may prevent potential units from being lost due to constraints, such as a creek, or may allow a small increase in units without giving up a sense of open space.
Examples of Codes
- Kirkland Municipal Code Sec. 22.28.042 – Allows for small-lot, single-family dwellings in specific zones
- University Place Municipal Code Ch. 19.53 – Standards and guidelines for small-lot development
Mixed use development is an important component of successful transit-oriented development, traditional neighborhood development, and smart growth/livable community development schemes. Mixed use developments contain a complementary mix of uses such as residential, retail, commercial, employment, civic and entertainment uses in close proximity - sometimes in the same building. Compatibility issues are addressed through performance standards, transition tools, careful site layout and building design, rather than by separating uses into single use zones.
When a wide variety of uses are located in close proximity to each other, walking and cycling become practical means of travel. For mixed use development to succeed, varied land uses must be within convenience walking distance of each other (one quarter mile, 5-10 minutes) and there must be direct, safe, and convenient connections between the uses. Residents in mixed use developments can take care of many daily needs without having to drive elsewhere. Mixed use development allows convenient access between work, home and other uses and services. In addition, mixed use development can contribute vitality and interest for residents, additional customers for neighborhood businesses, and a variety of housing choices.
Examples of Design Manuals, Best Practices, and Reports
- Antioch (CA): Mixed Use Design Guidelines – This manual provides clear and useful recommendations for the design, construction, review, and approval of mixed-use developments
- Oregon Transportation and Growth Management (TGM) Program: Commercial and Mixed Use Development Code Handbook – This comprehensive guide includes policies, best practices, and model code. Although a bit older, it is still a highly useful guide.
- Commercial Real Estate Development Association (NAIOP): Empirical Study of the Efficacy of Mixed-Use Development (2011) – Identifies issues, current state, and key success factors for mixed use development. Ares 2011 Best Research Paper award.
Examples of Codes
- Clark County Code Sec. 40.230.020, and Appendix A: Mixed Use Design Standards
- Issaquah Municipal Code Sec. 18.07.370 – Residential Mixed Use Developments
- Puyallup Municipal Code Ch. 21.31 – Mixed Use Zones
- Sumner Municipal Code Ch. 18.26 – Planned Mixed Use Development (PMUD)
- Thurston County Code Ch. 21.23 – Mixed Use High Density Corridor and Ch. 21.22 – Mixed Use Moderate Density Corridor (Lacey UGA)
- Tumwater Municipal Code Ch. 18.20 – Mixed Use Zone District
TOD is designed to increase the number of residents, employees, and potential transit riders that have convenient access to transit. A complementary mix of uses, activities, and services located in close proximity to each other allow TOD residents to commute to work, run errands, recreate, and meet basic needs without needing a car. A variety of moderate and higher density housing options located within easy walking distance from a centrally-located transit station or transit corridor (about 1/4 mile, 10 minutes) are typically a part of the mix.
For more information, see our page on Transit-Oriented Development.
This type of development may be difficult to institute because of the need for environmental assessment and the potential liability issues involved. A property owner may find it more advantageous to leave the property abandoned because development or sale may require a costly clean-up or spur a lawsuit—but this is changing. State and federal environmental laws and policies over the past few years have addressed some of these issues and are now focusing on how to turn brownfields into opportunities for investment.
In 2013, the Washington State Legislature made significant changes in the Model Toxics Control Act (MTCA) to facilitate clean up and redevelopment of brownfields. Changes of interest to local government include providing for model remedies to facilitate development of low risk sites, and granting authority for local governments to establish redevelopment opportunity zones where additional tools and resources, such as a revolving loan fund, will be available. An example of effective implementation of a local government brownfield development program can be seen with Spokane’s Brownfields Program. Notably, Spokane is home to Washington’s first and third Brownfield Redevelopment Opportunity Zones (ROZ).
Laws and Regulations
- U.S. Environmental Protection Agency (EPA): Brownfields Laws and Regulations
- Washington State Department of Ecology
A greyfield refers to an old, abandoned, or underutilized property used for retail or commercial shopping such as a mall. Developing these properties typically does not involve the environmental concerns seen with brownfield development but can demand the replacement or improvement of old infrastructure. Greyfield development can be advantageous largely because the infrastructure (foundation, plumbing, sewerage, electrical) can be salvaged. Greyfields are often developed into mixed use properties that are also transit-oriented.
Examples of Codes
- Port Townsend Municipal Code Ch.17.18 – Mixed Use Districts; and Ch. 17.40 – Mixed Use Developments
- Vancouver Municipal Code Ch. 20.430 – Commercial and Mixed Use Districts
- Chicago Metropolitan Agency for Planning: Greyfield/Suburban Retrofit – Strategies and case studies for greyfield development
- Congress for the New Urbanism: Greyfield Regional Mall Study (2001) – Initial analysis of greyfield properties and market opportunities
- Congress for the New Urbanism and U.S. Environmental Protection Agency: Malls Into Mainstreets (2005) – Comprehensive guide for greyfield development models, opportunities, and other information
If communities are to succeed in promoting infill development, they will need to recognize and overcome impediments to such development. Neighborhood opposition, financing challenges, inflexible building codes and development regulations, lengthy permit processes, substandard infrastructure, and other conditions may need to be addressed to attract infill development.
This section provides examples of how cities in Washington and elsewhere are changing their policies and offering incentives to encourage infill development.
Examples of Incentives to Facilitate Infill Development
- Bellingham Ordinance No. 2015-12-048 (2015) – Establishes an infill incentive program that reduces system development charges and permit fees for infill development in targeted areas
- Everett Potential Infill Measures (2013) – Outlines 20 potential infill strategies, including incentives for private land assembly
Outside Washington State
- Miami Dade County (FL) Infill Housing Initiative Guidelines (2017) and Infill Housing Developer Requirements – Provides incentives to encourage developers to build affordable housing and redevelop vacant, dilapidated, or abandoned properties in urban neighborhoods. Miami-Dade County has designated infill target areas and the established infill program offers incentives, including release from county liens, impact fee refunds, low interest loans, an expedited building permit process, and more.
- San Diego (CA) Expedite Program for Affordable/in-Fill Housing & Sustainable Buildings (2022) – Allows expedited permit processing for affordable infill housing developments that have 10 or more proposed units and are located within designated urbanized areas
- Spokane Infill housing strategies – Includes revised infill-related code sections and summaries of the revisions.
- Sultan Unified Development Code Ch. 16.34 – Offers a simple, small city example of standards for infill development in residential areas
- Tacoma Municipal Code Ch. 13.05 – Includes supplemental provisions for small-lot, single-family residential development, ADUs and Cottage Housing
- Vancouver Municipal Code Ch. 20.920 – Addresses infill development standards
- Ch. 36.70A RCW – The Growth Management Act
- RCW 43.21C.299 – Infill development - Categorical exemptions from chapter (SEPA)
- Ch. 35.100 RCW – Downtown and neighborhood commercial districts (sales and use tax increment financing)
- Portland (OR): The Infill Design Toolkit - Medium Density Residential Development (2008) – This exceptionally useful guide and toolkit contains a wide range of strategies for context-sensitive infill development, prototype designs that allow fast-track approval, technical design details, and a compilation of Portland neighborhood design policies.
- Association of Monterey Bay Area (CA) Governments (AMBAG): Infill Development Toolkit (2016) – Provides example of 11 different types on infill development configurations
- Center for Urban Policy Research: Infill Development Standards and Policy Guide (Revised Draft) (2007) – Very comprehensive guide and model ordinance with commentary; also describes challenges and proposes best practices solutions from successful programs in other places
- Harvard University: Patching the Fabric of the Neighborhood - The Practical Challenges of Infill Housing Development for CDCs (2007) – Covers methods for estimating infill potential, market considerations, infill housing typologies, and other useful information
- Lincoln Policy Institute: Gentle Infill - Boomtowns are Making Room for Skinny Homes, Granny Flats, and Other Affordable Housing (2018) – Examines infill efforts in Portland, OR, Boulder, CO, and Cambridge, MA
- Opticos Design: Missing Middle Housing – Provides a variety of helpful resources for housing types ranging in size from duplexes to courtyard apartments
- U.S. Environmental Protection Agency: Attracting Infill Development in Distressed Communities 30 Strategies (2015) – Outlines strategies for promoting infill, such as expediting permitting and creating new funding mechanisms for infill projects