Missing Middle Housing: How Localities Are Streamlining Efforts for ADUs and Other Building Types

Land Development
Contact: Nicholas Julian
Senior Program Manager, Land Use
(202) 266-8309

Accessory dwelling units (ADUs) are being utilized across the country to support aging parents or children, to keep family close together and provide lower-cost housing alternatives. Also known as in-law suites or granny flats, ADUs can be detached, garage-style conversions or attached to main homes in basements or separate units. They can add subtle density and increase the number of housing units in a neighborhood while maintaining character.

NAHB has been promoting this type of housing as a way to provide a variety of housing choices at varying price points to meet the needs to a changing nation. ADU development is not allowed in many areas of the country, however, because of single-family zoning.

One area, though, that is actively pursuing ADU development is Sacramento, Calif. In January 2023, the city released permit-ready one- and two-bedroom ADU plans that meet all local residential building code requirements and are all electric.

Creating pre-approved plans streamlines the development process for these housing types; residents can immediately begin seeking a permit after submitting a site plan. Additionally, at 750 square feet, the plans are not subject to impact fees.

Sacramento’s efforts fit within California’s broader efforts to address the severe housing crisis within the state. California State Bill 9 (SB9), effective Jan. 1, 2022, now allows home owners to divide their properties and construct two new units on each lot, effectively legalizing fourplexes in areas that previously allowed only one unit.

SB9 was passed along with State Bill 10 and authorizes local government to zone up to 10 homes per parcel in transit-rich areas or urban infill sites. The California Building Industry Association (CBIA) advocated for the passage of SB9 and SB10, and worked to dispel misinformation about what the bills would and would not allow.

While primary ADU legalization laws (AB 68 and AB 881) were passed statewide in 2019, Assembly Bill 2221 (AB 2221), signed into law in September 2022, clarifies ADU development rules and helps close regulatory loopholes. AB 2221 helps reduce arbitrary local decisions that prevent ADUs, such as preventative front setback requirements, and requires permitting agencies to return comments on proposed ADUs within 60 days.

The total number of ADUs permitted in California rose from just shy of 9,000 in 2018 to nearly 24,000 in 2021, according to the California Department of Housing and Community Development.

New land use policy initiatives often include ADUs within a larger promotion of missing middle housing, or housing that is neither traditional single-family nor large multifamily, and includes ADUs, duplexes, triplexes, and small-scale apartment buildings.

The Terner Center for Housing Innovation at UC Berkeley released a report, Unlocking the Potential of Missing Middle Housing, in December 2022 on how to further improve missing middle housing policy. The report mentions that builders have seen a great demand for missing middle projects, but particular policy barriers still exist, such as design requirements that make projects difficult. A streamlined approval process, including “clear and consistent rules, expedited reviews, dedicated staff, and pre-approved plans,” would help facilitate small-scale development.

Other HBAs have been actively supporting similar legislation in their states, including the Building Industry Association of Washington (BIAW). BIAW, along with the Spokane Home Builders Association, has supported HB1110, which would allow fourplexes on all residential lots in cities with populations of 6,000 or greater and would require cities with populations greater than 6,000 to allow sixplexes on all lots if at least two of the units are affordable or if the lot is within a half mile of a major transit stop. The city of Spokane is set to release preapproved missing middle housing plans to streamline approvals for duplexes, townhouses and fourplexes. Spokane joins Sacramento and South Bend, Ind., where preapproved multifamily infill housing designs were released in 2022.

For more information on missing middle housing, check out NAHB’s Land Use 101 toolkit. Other resources include AARP’s Accessory Dwelling Units: A Step by Step Guide to Design and Development, which contains example policies and projects from Austin; Washington, D.C.; Denver; and Oakland, Calif.

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