What Is Missing Middle Housing? Zoning Rules and What You Can Build

Missing middle housing is the range of building types between a detached house and a mid-rise apartment building: duplexes, triplexes, fourplexes, townhouses, cottage clusters, and small courtyard buildings. It is called missing because many zoning codes allow only detached houses in most residential districts, so these types stopped being built there. Reform laws now re-legalize them, usually by setting a number of homes that must be allowed on any residential lot.

What counts as middle housing

There is no single legal definition. Each law writes its own list.

• Oregon's HB 2001 defines middle housing as duplexes, triplexes, quadplexes, cottage clusters, and townhouses, according to the state's fact sheet.
• Washington's middle housing statute names nine types and requires covered cities to allow at least six of them.
• New York City uses the term for three to five story apartment buildings on qualifying sites near transit.

How the laws work

Most middle housing laws set a minimum number of homes that a city must allow on a lot in any zone that allows a detached house. The base district name, such as R-1, often stays the same.

• Oregon, HB 2001 (2019). The law required cities of 10,000 to 25,000 people outside the Portland Metro boundary to allow a duplex on each residential lot that allows a detached house, and cities over 25,000 and Portland Metro jurisdictions to also allow triplexes, quadplexes, cottage clusters, and townhouses. The first local deadlines were June 30, 2021 and June 30, 2022. The state's current rules, amended effective September 14, 2026, lower the medium city threshold to 2,500 people, and a state model code applies directly to a city that has not acted by January 1, 2027.
• Washington, HB 1110 (2023). Cities of 25,000 to 75,000 must allow at least two units per residential lot, and four within a quarter mile walking distance of a major transit stop or where one unit is affordable. Cities of 75,000 or more must allow four units per lot, and six near a major transit stop or where two units are affordable.
• California, SB 9 (2022). Two homes on a single-family lot, plus a lot split, for up to four homes where one was allowed. See our SB 9 explainer.
• Austin, HOME Phase 1. Adopted December 7, 2023, with applications accepted from February 5, 2024, it allows up to three housing units on a lot zoned SF-1, SF-2, or SF-3, per the city's HOME amendments page. See our Austin zoning guide.
• New York City, City of Yes (2024). Allows three, four, or five story apartment buildings in low-density districts on sites that are near a subway or rail station, at least 5,000 square feet, and on the short end of a block or facing a street at least 75 feet wide. See our City of Yes explainer.

What this lets you build

On an ordinary house lot. In a covered city, a lot that used to allow one house can now take two to four homes without a rezoning, and up to six near transit in Washington's largest cities.

Which parcels are affected. Check each of these:

• City size. Oregon and Washington set population tiers, and smaller cities are exempt or have lower numbers.
• The zone. The laws attach to zones that allow detached single-family homes. They do not change commercial or industrial districts.
• Transit distance, where the law grants extra units near a stop.
• Lot-level exemptions. Washington exempts critical areas and their buffers, certain watershed and aquifer areas, and lots that fall below 1,000 square feet after subdivision.

What approvals are removed. The added units are a permitted use, so there is no rezoning or conditional use permit for the unit count. In California, an SB 9 application must be decided ministerially within 60 days. Oregon lets cities regulate siting and design only if the rules do not discourage middle housing through unreasonable cost or delay.

What limits remain. The unit count is allowed, but the building still has to fit. Check:

• Setbacks, height, and lot coverage. Austin caps impervious cover at 45 percent and building coverage at 40 percent for its two-unit and three-unit uses.
• Parking. Washington bars cities from requiring off-street parking for middle housing within half a mile of a major transit stop, and caps it at one space per unit on lots of 6,000 square feet or less. See parking minimums.
• Private covenants. Oregon's law bars new covenants that prohibit middle housing, which leaves existing deed restrictions for you to check in title.
• Conditions on the right itself. An SB 9 lot split requires the applicant to sign an affidavit of intent to live in one of the units for three years, and SB 9 units cannot be rented for terms of 30 days or less.

How to check a specific parcel

1. Confirm the city's population tier and whether the law has taken effect locally.
2. Confirm the parcel's zoning district allows detached single-family homes.
3. Read the city's middle housing standards for lot size, coverage, height, and parking.
4. Measure the distance to the nearest qualifying transit stop if extra units depend on it.
5. Pull title and check for deed restrictions or homeowners association rules.

In Plotzy, filter parcels by zoning designation and lot size to find residential lots large enough for the type you build, then ask Zoning AI "How many dwelling units are allowed on this lot, and what are the setbacks?" for an answer with the code section cited.

Frequently asked questions

What is missing middle housing?

It is housing at a scale between a single detached house and a large apartment building: duplexes, triplexes, fourplexes, townhouses, cottage clusters, and small apartment buildings.

Is a duplex allowed on a single-family lot?

It depends on the state and city. Oregon's current rules require it in cities over 2,500 people, Washington in cities of 25,000 or more, and California allows two units on qualifying single-family lots under SB 9. Elsewhere it depends on the local district. An R-2 district usually allows duplexes, and an R-1 district usually does not.

How many units can I build on a residential lot under these laws?

Typically two to four. Washington allows up to six per lot in its largest cities near major transit or with affordable units. Austin allows three on SF-1, SF-2, and SF-3 lots. California's SB 9 allows up to four across two lots after a lot split.

Do HOA rules still apply?

Often, yes. State middle housing laws change what a city may prohibit through zoning. Private deed restrictions and homeowners association covenants are a separate layer, and only some laws address them.

Sources

The bills, statutes, court decisions, and agency documents cited on this page were checked on October 4, 2026. These laws have been amended and litigated since they passed, so confirm the current text and status before relying on any detail. This page is general information, not legal advice.

• Oregon Department of Land Conservation and Development: Key Elements of House Bill 2001. The 2019 law's city tiers, housing types, first deadlines, siting and design limit, and covenant rule.
• Oregon Secretary of State: Oregon Administrative Rules, Chapter 660, Division 46 (Middle Housing in Medium and Large Cities). Current definitions of medium and large cities, the September 14, 2026 amendment, the January 1, 2027 model code date.
• Washington State Legislature: RCW 36.70A.635. Units per lot by city size, transit and affordability bonuses, the nine housing types, parking limits, exemptions.
• Washington State Legislature: HB 1110 (2023) bill summary. Chapter 332, Laws of 2023.
• California Legislative Information: Government Code Section 65852.21. Two units on a single-family lot, 60-day ministerial decision, rental term.
• California Legislative Information: Government Code Section 66411.7. Lot split and the owner-occupancy affidavit.
• City of Austin: HOME Amendments. Phase 1 dates, three units per lot, coverage limits.
• NYC Department of City Planning: transit-oriented development guide. Qualifying sites, story limits, the "missing middle" label.