Portland, Oregon is one of the cities leading the national trend toward expanding housing options in what have been exclusively single-family zone districts, enabling small-scale “missing middle” multifamily housing in residential neighborhoods.
Portland's Residential Infill Project website includes background material, the approved zoning ordinance and other design guidance for those interested in building duplexes, triplexes and fourplexes in Portland’s neighborhoods.
This website can serve as guidance for California jurisdictions that may also be considering zoning changes in single-family neighborhoods.