Commonwealth Building, International Style commercial high-rise in Portland, United States

Commonwealth Building is a 14-story commercial structure with a distinctive sea-green glass exterior and aluminum frame located at 421 SW 6th Avenue. The slim profile and smooth facade showcase the clean lines characteristic of International Style design.

Pietro Belluschi designed the Equitable Building, constructed from 1944 and opened in 1948 as the Portland headquarters of Equitable Savings and Loan Association. Originally planned for 12 stories, it rose to 14 and was the first tower sheathed in aluminum, the first with double-glazed window panels, and the first fully sealed and air-conditioned. Renamed Commonwealth Building in 1965, it joined the National Register of Historic Places in 1976.

The building marked a turning point in how cities could look, showing that glass and metal could define a modern commercial tower. Its design approach spread to office buildings across the country and changed what people expected from urban architecture.

The building sits in downtown Portland and is straightforward to find and access. A fitness center with shower facilities and basement bicycle storage offer practical conveniences for those visiting or working on-site.

In 1980 the American Society of Mechanical Engineers named it a National Historic Mechanical Engineering Landmark, citing one specific feature: it was the first large commercial building in the United States to use heat pumps for heating and cooling. The system ran on well water, not geothermal heat from the earth, so the honour rests on the pumps themselves.