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In Portland Oregon many ADUs are converted unattached garages, finished attics, finished basements and more rarely converted garden sheds. Particularly, in the areas where much of the closer to city center housing stock is pre-World War 2 and near good public transit.

ADUs have to meet current building and fire codes. Though there is a loophole where an on-site resident owner may do their own construction without permits.

ADU construction along with rental housing starts is also slowing due to recent city legislation and the threat of rent control which has been illegal in the entire state of Oregon since the 1980s. And the city of Portland via new regulation has already added friction and increased costs in their rental market exacerbating their "rental housing crisis" except for those renters already in existing rentals.

ADUs were popular additions on family occupied and/or owned Portland properties until the recent regulatory changes and rent control threat. Now there is added known risk and uncertainty.