On October 15, District of Columbia Mayor Muriel Bowser and the Office of Planning released a draft of their Comprehensive Plan. The plan focuses on affordable housing as a top priority – which, in case you didn’t know, is a major issue throughout the city. Rent costs in Washington, D.C. have risen dramatically since 2012; average rental rates currently sit between $2300 and $3100 per month depending on the data used (the dependability of rental data is for another day). This requires a household to earn at least $83,000 per year – or an hourly wage of $39.22. In fact, the number of rental units affordable to lower income residents has decreased, even though population and total units available have increased. Supply simply isn’t meeting demand and the new units being built are luxury units geared towards the upper end of the market. Affordable housing in safe, transit-accessible neighborhoods with access to important services and amenities is dwindling. Fortunately, Mayor Bowser’s administration has recognized this as a major impediment to creating an equitable city in the 21st Century.
The plan dictates an ambitious city-wide goal of 36,000 new housing units, 12,000 of them affordable, by 2025. The Housing Equity Report was released with the draft of the plan and contains housing goals for the city’s 10 planning areas – a refreshing approach to policy guidance. The plan cites several strategies and policies to help achieve these goals, including inclusionary zoning policies, an affordable housing acquisition fund, and affordable housing requirements for new developments. All of this indicates that the District of Columbia is taking its housing affordability issue seriously. But one of the most scalable housing solutions available is virtually omitted from these plans: accessory dwelling units, or ADUs. In layman’s terms, an ADU is any residential unit separate from the main structure, like a guesthouse or mother-in-law apartment over the garage. Providing incentives, like property tax credits or subsidized affordable units, for ADUs would jump-start their construction on some of the 63 million square feet of available land throughout the city.
63 million square feet is a lot of real estate. So where does that number come from? I conducted a spatial overlay analysis of single-family building footprints and residential property area and it revealed that ADUs could significantly help the District of Columbia meet its goal of 36,000 new units. In D.C., properties with single-family homes are eligible to build an ADU that uses 30% or less of the remaining lot area. GIS analysis of the entire city shows that there’s 63.4 million square feet eligible for ADU development on single-family residential properties. Assuming approximately an average unit of 300 square feet and 150 square feet per person, that’s potentially 211,000 units housing nearly 422,000 people. Of course, it’s not possible for every property to build an ADU. Assuming as little as one in ten properties construct an ADU, that’s still 21,000 units. And if the District decided to increase the maximum remaining lot coverage to 40% then we’re talking over 28,000 units.
Not all neighborhoods are created equal either. Just like the District of Columbia’s Housing Equity Report, ADU distribution targets were measured for each community planning area. The number of potential ADUs varies depending on the community. This is due to different zoning, land use and density characteristics for certain neighborhoods. Because of the large number of single-family properties, the Near Northeast, Far Southeast and Rock Creek West areas have the greatest potential for ADU expansion, whereas a denser, mixed-use area like Central Washington has virtually no space for ADUs. Understanding the geography of ADU expansion would be useful if the District were to consider locating pilot policies or programs in specific neighborhoods.
These numbers are impressive, albeit imperfect. There are plenty of lots probably too small for any ADU development; however, even the conservative projections show there’s plenty of room to grow. ADUs may not be ideal for families but they are an incredible housing option for a significant portion of the population, such as students, creatives, and seniors. If designed correctly, ADUs can be built efficiently and quickly. They also provide many of the same benefits of a home – accessibility, privacy, natural light – without the overwhelming square footage. Long story short, ADUs are marketable, affordable and, most importantly, scalable – there’s plenty of space for them. If the District of Columbia wants to add 36,000 housing units to the market in five years, incentivizing and subsidizing ADUs would be a good place to start.