Duplexes to fourplexes in the permit record
Buildings of two to four units, the duplexes, triplexes and fourplexes, supplied 3.5% of the housing units authorized in the United States from 2021 to 2025: 55,741 units in 2025. The share is small nationally but reaches a quarter or more of new units in a handful of metro areas.
In the permit survey these buildings form two classes, two-unit and three-to-four-unit, which this site adds together. A duplex permit counts two units, a fourplex four. The class sits between single-family houses and apartment buildings, a group often called the "missing middle".
The national count
| Year | Units in 2–4 unit buildings | Share of all units |
|---|---|---|
| 2004 | 90,384 | 4.4% |
| 2006 | 76,604 | 4.2% |
| 2009 | 20,690 | 3.5% |
| 2012 | 25,901 | 3.1% |
| 2015 | 32,077 | 2.7% |
| 2018 | 39,696 | 3% |
| 2021 | 52,853 | 3% |
| 2023 | 54,716 | 3.6% |
| 2024 | 54,468 | 3.7% |
| 2025 | 55,741 | 3.9% |
The share fell from 4.4% in 2004 to a low of 2.7% in 2015 and has edged up since, to 3.9% in 2025. In units, 2025 was the busiest year for this class since 2007.
Where small multi-unit buildings matter
| Metro area | 2–4 share, 2021–2025 | Units, 2021–2025 |
|---|---|---|
| Wichita, KS | 39% | 5,763 |
| Fort Smith, AR-OK | 36% | 1,175 |
| Jonesboro, AR | 27% | 1,465 |
| McAllen-Edinburg-Mission, TX | 27% | 9,186 |
| Pocatello, ID | 24% | 553 |
| Bismarck, ND | 24% | 587 |
| New Orleans-Metairie, LA | 19% | 2,028 |
| Tyler, TX | 17% | 611 |
| Abilene, TX | 16% | 618 |
| Providence-Warwick, RI-MA | 16% | 1,829 |
| Atlantic City-Hammonton, NJ | 15% | 1,135 |
| Eau Claire, WI | 15% | 842 |
The leaders are small and mid-sized metro areas. Wichita stands out at 39%. Among the large metro areas, Providence has the highest share (16%), followed by Milwaukee (9.9%).
By state the share is highest in Rhode Island (20%), Kansas (16%) and Alaska (12%).
Where they are almost absent
In 25 of the 387 metro areas, two- to four-unit buildings made up less than half a percent of 2021–2025 units. A share this small often reflects how few such buildings are put up at all, but it can also mean that a local office files small multi-unit buildings differently; the survey takes the classification each office reports.
The largest counts by state
Shares favor small places where a few buildings matter; raw counts show where most of these units are actually authorized.
| State | Units in 2–4 unit buildings, 2021–2025 | Share of the state total |
|---|---|---|
| Texas | 39,893 | 3.3% |
| California | 21,271 | 3.8% |
| Florida | 20,064 | 2.1% |
| Washington | 12,428 | 5.8% |
| Arizona | 9,882 | 3.3% |
| New Jersey | 9,486 | 5.6% |
By metro size the share barely changes: 2.9% for metro areas of 1 million or more, 4.5% for metro areas of 500,000 to 999,999, 3.2% for metro areas of 250,000 to 499,999, 4.9% for metro areas of under 250,000. The national figure of 3.5% reflects these buildings being uncommon almost everywhere rather than concentrated in one kind of place.
The six largest metro areas
The table compares the boom years with the latest five years for the six most populous metro areas.
| Metro area | 2–4 share, 2004–2006 | 2–4 share, 2021–2025 |
|---|---|---|
| New York-Newark-Jersey City, NY-NJ | 23% | 4.4% |
| Los Angeles-Long Beach-Anaheim, CA | 4.5% | 6.4% |
| Chicago-Naperville-Elgin, IL-IN | 6.5% | 5.5% |
| Dallas-Fort Worth-Arlington, TX | 1.2% | 2.4% |
| Houston-Pasadena-The Woodlands, TX | 0.8% | 2.2% |
| Atlanta-Sandy Springs-Roswell, GA | 0.7% | 1.4% |
Where the count grew most
Measured as the change in yearly units between 2004–2006 and 2021–2025, the largest increases among the metro areas profiled here were in Dallas (from 704 to 1,759 a year), Houston (from 536 to 1,526 a year), Wichita (from 208 to 1,153 a year), McAllen (from 1,097 to 1,837 a year), Philadelphia (from 521 to 1,030 a year). Because the class is small, a handful of projects can move these figures quickly in either direction.
Shifts by state
Comparing 2004–2006 with 2021–2025, the two-to-four share rose most in Kansas (5.6% to 16%), Rhode Island (9.6% to 20%), Wyoming (5.8% to 8.6%), Oklahoma (3.4% to 6.2%) and fell most in New York (19% to 3.7%), Alaska (22% to 12%), New Jersey (13% to 5.6%), Montana (14% to 10%). Both lists mix large and small states, so the change is not one national movement in a single direction.
Counting units, not buildings
Because the survey counts units, a fourplex weighs twice as much as a duplex in these shares. Nationally the 55,741 units of 2025 correspond to somewhere between about 13,935 buildings (if all were fourplexes) and 27,870 (if all were duplexes); the survey's building counts sit between those bounds. For comparison, the 911,903 single-family units of the same year are also 911,903 buildings.
Put another way, for every 100 single-family houses authorized in 2025 there were about 6 units in two- to four-unit buildings and 51 in buildings of five or more. In 2005 the same ratios were 5 and 23.
What the share can show
Because the class is small, a single developer building a few dozen duplexes can move a mid-sized metro area's share by several points. Read the share together with the unit count in the table. The area pages show the two-to-four share as the ochre segment of each yearly column and of the mix bar.
A change in local zoning that allows more of these buildings would show up here only once projects are permitted; the survey records permits, not rules. For the bigger picture of houses against apartments see the mix briefing.
Sources
US Census Bureau, Building Permits Survey, annual county and state files 2004–2025; OMB metro area delineation of July 2023; US Census Bureau, Population Estimates, Vintage 2025. All figures computed by this site; see the counting rules.