Why Have ADUs Proliferated in Portland, Lagged in D.C.?

A new report by the Urban Institute examines the consequences of small differences in land use regulations.

November 11, 2020, 5:00 AM PST

By James Brasuell @CasualBrasuell


Accessory Dwelling Unit

radcliffe dacanay / Flickr

"Why did accessory apartments catch on in Portland but not DC? A new study from the Urban Institute compares the land-use reform process in each city, as well as the end result."

Libby Solomon shares news of a newly published comparative analysis of the efforts of two cities to allow accessory dwelling units (ADUs): Portland and Washington, D.C.

The premise of the analysis: that Portland has been far more successful in achieving the desired development of ADUs, despite the similar intentions of land use reforms passed in the past decade in each city, both with similar development histories and populations.

"But that’s where the similarities end," writes Solomon to summarize the findings of the report. "[W]hile Portland’s accessory units skyrocketed, with hundreds built each year, DC’s accessory apartments saw a much smaller bump. From 2017 through 2019, Portland issued more than 1,500 ADU building permits; DC issued only 68."

According to the Urban Institute's analysis, property owners in D.C. face structural and historical issue that make ADUs significantly more difficult and expensive to build.

"In the end, DC’s new zoning regulations passed allowing accessory units by right in residential zones. But those regulations are more restrictive than advocates wanted," writes Solomon. "The Urban Institute researchers write that ADU regulations are too complex for many to navigate without hiring lawyers and architects; the space requirements cut out many potential builders; and the rules require the owner to live on the property."

A lot more analysis and insight into the findings of the report are available in the source article.

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