Beginning in the nineteenth century, and continuing into the first decades of the twentieth century, an extensive system of streetcars helped link outlying districts to the city center. The streets on which these streetcars were located developed with mixed residential and commercial uses, with commercial uses appearing either in new buildings or as extensions to residential buildings. A study done by graduate students Dan Childs and Dan Nowell looked at residential buildings with commercial extensions that appear mostly on these streets. They found that these building extensions are of several different types, house a variety of kinds of businesses, and are still being built in some neighborhoods. The model represents a typology that allows home businesses to expand "in place," and is allowed as of right in many places with appropriate zoning.
A second project, also carried out by graduate students, involved the East Side Industrial District (ESID) located just across the Willamette River from the city's downtown core. The ESID is regarded as an "industrial sanctuary," and has been able to resist many of the forces of gentrification and re-zoning for market-rate housing that are typical in similar districts in Portland and other cities. By investigating the trajectories of several businesses in the district—as well as the histories of the buildings in which those businesses are now located—our study suggested why the ESID is able continue to harbor small, start-up businesses. This ability is due to a number of factors, including the small size of the Portland block, the district's proximity both to the downtown and to residential districts, and the city's willingness to maintain industrial zoning in the district—even in the face of other development pressures.