A Portland-Brand Building Boom: Accessory Dwelling Units

"Portland's new housing stock is getting miniaturized, with builders planning nearly as many accessory dwelling units as regular single-family houses," reports Steve Law.

Law is sharing data from the city's Bureau of Planning and Sustainability and Bureau of Development Services, which shows "the city issued 615 building permits for new accessory dwelling units or ADUs in 2016, approaching the 867 permits issued for regular houses."

The news is partly enabled by the tough conditions for single-family housing construction in the city. "One reason single-family construction seems to have plateaued is the lack of undeveloped large parcels of land, forcing homebuilders to focus on infill homes on vacant lots or replacing demolished homes, rather than traditional subdivisions," explains Law.

Still, the city of Portland's ADU laws are considered lenient, and the cost of constructing an ADU at the maximum size of 800 square feet is about $160,000. Planetizen last checked in with the effects of Portland's ADU regulations in 2014, after a study found that the units create relatively low impacts from increased automobile traffic. Since then, however, more cities are following Portland's example.