Small to Medium Multifamily Housing by the Numbers
This brief presents a quantitative national profile of the small to medium multifamily (SMMF) housing stock (units in buildings with 2-49 units, including both rental and owner-occupied units unless otherwise specified). This includes a characterization of the stock itself, how it has changed over time, the demographic characteristics of SMMF residents, and conditions in the neighborhoods where SMMF units are located.
Quantifying the SMMF Housing Stock
Growth in the SMMF stock has been slow since 2010
According to the 2020 5-Year American Community Survey, there are about 28,281,000 SMMF housing units in the U.S. While this number has been growing, that growth has slowed since 2010 – the SMMF stock grew by 12.8 percent from 2000 and 2010 and just 2.7 percent from 2010 to 2020.
Units in SMMF Buildings, 2000-2020
Source:2011-2015 and 2016-2020 ACS 5-year Estimates and 2000 and 2010 Decennial Census
Most SMMF units were built before 1980
55 percent of SMMF units nationwide were built prior to 1980. Because units built before 1978 may contain lead-based paints, this will be a potential concern for rehabilitation in buildings that have not already undergone lead paint abatement.
SMMF Units by Year Built
Source: ACS 2020 5-year Estimates
More than one third of SMMF units are in 2-4 unit buildings
Units in duplex, triplex and quadplex buildings represent 38 percent of all SMMF units. The remaining units are split roughly evenly between 5-9 unit, 10-19 unit and 20-49 unit buildings.
SMMF Units by Units in Structure
Source: ACS 2020 5-year Estimates
Who Lives in SMMF Housing?
Most SMMF rental units are affordable to low-income households
About 80 percent of SMMF rental units are affordable to households with incomes at or below 80 percent of the local area median income. In addition, SMMF units comprise more than half (52 percent) of all housing that is affordable at this income range. This makes them a critical source of affordable housing nationwide.
Rental Units by Affordability Level and Units in Structure
| Units in Structure | 0-60% AMI | 61-80% AMI | 81-100% AMI | 101-120% AMI | 121% AMI or More | Total | |
| Mobile home or trailer | 1,633,756 | 301,370 | 60,899 | 12,369 | 6,646 | 2,043,851 | |
| Boat-RV-van | 36,717 | 4,696 | 1,264 | 670 | 707 | 50,239 | |
| 1-unit house, attached | 1,226,006 | 799,909 | 563,013 | 193,347 | 128,274 | 2,928,762 | |
| 1-unit house, detached | 6,020,987 | 3,157,755 | 1,987,982 | 823,756 | 588,970 | 12,728,985 | |
| SMMF Properties | 2 -unit building | 2,114,576 | 816,188 | 343,526 | 94,033 | 62,375 | 3,452,834 |
| 3-4 -unit building | 2,775,383 | 1,220,499 | 545,920 | 165,695 | 102,163 | 4,826,638 | |
| 5-9 -unit building | 2,852,614 | 1,510,577 | 704,428 | 212,699 | 120,537 | 5,415,882 | |
| 10-19 -unit building | 2,445,981 | 1,582,585 | 820,507 | 233,116 | 132,473 | 5,229,583 | |
| 20-49 -unit building | 1,896,886 | 1,137,082 | 673,511 | 234,326 | 230,141 | 4,194,332 | |
| 50+ unit building | 2,547,222 | 1,223,988 | 1,089,145 | 571,419 | 909,741 | 6,419,283 | |
| Total Units | 23,550,129 | 11,754,648 | 6,790,193 | 2,541,429 | 2,282,026 | 47,307,367 | |
| All SMMF (2-49 unit buildings) | 12,085,441 | 6,266,931 | 3,087,891 | 939,868 | 647,689 | 23,079,940 | |
|
% of all Units at Affordability level that are SMMF |
51% | 53% | 45% | 37% | 28% | 49% | |
Source: Enterprise estimates based on 2016-2020 5 Year PUMS, 2022 HUD Income Limits, and the Missouri Data Center PUMA to County Crosswalk
Estimates include both occupied and vacant rental units
The Total Units column includes a small number of rental units for which rent amounts were not available and therefore affordability calculations could not be performed. Therefore, the Total Units column may be slightly higher than the sum of the other columns in the table.
Rental Units by Affordability Level
Source: Enterprise estimates based on 2016-2020 5 Year PUMS, 2022 HUD Income Limits, and the Missouri Data Center PUMA to County Crosswalk. Estimates include both occupied and vacant rental units. The Total Units column includes a small number of rental units for which rent amounts were not available and therefore affordability calculations could not be performed. Therefore, the Total Units column may be slightly higher than the sum of the other columns in the table.
Only a small fraction of SMMF units receive federal assistance
The vast majority (95 percent) of SMMF rental units that are affordable at 80 percent AMI or below are not federally subsidized using project-based subsidies. Of the 996,000 SMMF rental units that are subsidized, about 22% are set to expire by 2027 (within the next 5 years, as of writing).
SMMF Rental Units Affordable at 80% or Below by Subsidy Status
Source: National Housing Preservation Database, 2022; Enterprise estimates based on 2016-2020 5 Year PUMS; 2022 HUD Income Limits; and the Missouri Data Center PUMA to County Crosswalk. Estimates include both occupied and vacant rental units.
[1] This means the developments may still receive state and local subsidies or have residents who receive assistance through the Housing Choice Voucher or other tenant-based assistance programs.
SMMF residents are disproportionately BIPOC
Although the majority of SMMF householders are white, householders who are Black, Indigenous and people of color (BIPOC) disproportionately live in SMMF housing. Black or African American householders, in particular, have the highest rate of living in SMMF units compared to other types of properties.
Units by Type and Householder Race/Ethnicity
Units by Type and Householder Race/Ethnicity
Source:ACS 2020 5-year Estimate. Note that in the ACS, individuals identifying as Hispanic or Latino also identify as one of the racial groups shown.
[2] ‘Householder’ is a term used by the census to refer to the person in whose name the unit is rented or owned. In cases where the unit is jointly owned or rented, the person responding to the American Community Survey will choose one of these people to be the householder for the purposes of the response.
SMMF residents are disproportionately younger
SMMF units house a higher rate of younger householders. Although SMMF householders represent a wide range of ages, 37 percent of householders aged 15 to 34 live in SMMF housing compared to 17 percent aged 35 to 64 and 13 percent aged 65 or older.
Units by Type and Householder Age
Units by Type and Householder Age
Source: ACS 2020 5-year Estimates
SMMF households are disproportionately smaller
One-person households both represent the largest group and have the highest rate of living in SMMF housing, while larger (4- and 5-person) households tend to live in other types of housing.
Units by Type and Household Size
Units by Type and Household Size
Source: ACS 2020 5-year Estimates
What Neighborhoods are SMMF Units Located in?
SMMF units tend to be in neighborhoods with low homeownership rates
Nearly 70 percent of SMMF units are located in neighborhoods (census tracts) with lower homeownership rates (fewer than 60 percent of households own their home). By contrast, only 36 percent of housing units overall are located in these neighborhoods.
Units by Census Tract Homeownership Rate
Source: ACS 2020 5-year Estimates. Note: 288 census tracts excluded due to data availability.
SMMF units tend to be in neighborhoods with increasing rents
SMMF units are more likely than housing units overall to be located in neighborhoods where rents increased between the 2011-2015 and 2016-2020 ACS. Affordable SMMF units located in these neighborhoods are likely at higher risk of affordability loss through rising rents.
Units by Change in Census Tract Median Gross Rent, 2015 - 2020
Source: 2020 5-year ACS and PolicyMap calculation of census tract change in median gross rent 2011-2015 to 2016-2020
SMMF units are more likely to be located in majority BIPOC neighborhoods
Compared to housing units as a whole, SMMF units are more likely to be located in neighborhoods (census tracts) where the majority of residents are Black/African American, Asian and/or Hispanic/Latino. That said, more than half all SMMF units are located in neighborhoods where a majority of residents are white.
Units by Census Tract Majority Race/Ethnicity
Figure 10 ACS 2020 5-year Estimates
For more quantitative analysis of SMMF housing, see Understanding the Small and Medium Multifamily Housing Stock, a 2017 paper by researchers from Enterprise and the Sol Price School of Public Policy at the University of Southern California.