Joining the Los Angeles architectural firm Webber, Staunton and Spaulding, Duell contributed to designs for notable building projects in metropolitan Los Angeles during the 1920s and 1930s, among them the Avalon Casino on Catalina Island, Frary Dining Hall and adjacent residence halls at Pomona College, and Greenacres, the estate of silent movie actor Harold Lloyd in Beverly Hills.

As construction declined during the Great Depression, Metro-Goldwyn-Mayer hired Duell in 1936 to design the set of the Capulet home in Irving Thalberg's production of Romeo and Juliet.

Notable among his designs during this period is Casa de Cadillac, a car dealership in Sherman Oaks built in 1948 which is now considered a prime example of Googie architecture.

[4]: 55  One notable exception was at Magic Mountain, where the developers ran short of money before a planned tunnel could be dug to connect the loop at the rear of the park.

[5] The Duell office employed the talents of a number of former motion picture art directors and theme park designers, among them Robert H Branham, Leroy Coleman, John DeCuir, John DeCuir, Jr., Roger Duell, Paul Saunders, Ira West, Harry Webster, Art Pieper, and Paul Groesse.