Affordable Housing
This indicator reports the number and percentage of housing units affordable at various income levels. Affordability is defined by assuming that housing costs should not exceed 30% of total household income. Income levels are expressed as a percentage of each county’s area median household income (AMI).
Source
Source Description
The American Community Survey (ACS) is a nationwide survey designed to provide communities with reliable and timely social, economic, housing, and demographic data every year. The ACS has an annual sample size of about 3.5 million addresses, with survey information collected nearly every day of the year. Data are pooled across a calendar year to produce estimates for that year. As a result, ACS estimates reflect data that have been collected over a period of time rather than for a single point in time as in the decennial census, which is conducted every 10 years and provides population counts as of April 1. The Census Bureau combines 5 consecutive years of ACS data to produce estimates for geographic areas with fewer than 65,000 residents. These 5-year estimates represent data collected over a period of 60 months. Because the ACS is based on a sample, rather than all housing units and people, ACS estimates have a degree of uncertainty associated with them, called sampling error. In general, the larger the sample, the smaller the level of sampling error. Data users should be careful in drawing conclusions about small differences between two ACS estimates because they may not be statistically different.
For more information about this source, including data collection methodology and definitions, refer to the American Community Survey data user’s website.
Methodology
This indicator reports the number of housing units available to families with different income levels. Income levels are based on various percentages of Area Median Income (AMI). AMI is acquired for each county using data from the 2018-2023 American Community Survey (ACS). AMI is then used to determine affordable monthly housing payments at various income levels relative to AMI. For this assessment, affordability assumes that a family should pay no more than 30% of their income toward mortgage or gross rent. For example, the AMI for Washington, DC is $64,267. In DC, a family earning 40% of AMI earns $22,494 per year, or $1,875 per month. For this family to live in affordable housing, total monthly housing costs should not exceed $562.
Using these assumptions, the number of units affordable at each income level is estimated using ACS data on household value (for owner-occupied households) and gross rent (for renter-occupied households)*. In the ACS, these data are presented in the form of counts of units that fall in certain value ranges. For example, in Washington, DC there are 4,563 units with gross rents between $500 and $600. To determine unit counts affordable at certain income levels, a proportional allocation method is used. Using the example above, the total number of rental units affordable to a family that should spend no more than $562 on housing expenses is calculated as follows:
Units with GR under $562 =
[# GR $1.00 – $100] +
[# GR $100 – $200] +
[# GR $200 – $300] +
[# GR $300 – $400] +
[# GR $400 – $500] +
[# GR $500 -$600] * [(562 – 500) / 100]
Thus all units with gross rent (GR) in the ranges 0-100, 100-200, 200-300, 300-400, and 400-500 are counted, and around 60% of those units in the 500-600 range. Using this method, the data shows that there are approximately 20,024 units available to families earning 40% of AMI in Washington, DC.
For more information on the data reported in the American Community Survey, please see the complete American Community Survey 2023 Subject Definitions.
Data Breakouts Available
- Affordable Renter-Occupied Units, Aggregate Percentage
- Affordable Renter-Occupied Units by Income Level, Total
- Affordable Owner-Occupied Units, Aggregate Percentage
- Affordable Owner-Occupied Units by Income Level, Total