Staff Seargeant, U.S. Army Corps of Engineers, 1943-1945; Draftsman, Wolff, Portland, OR, 1946-1954; Partner, Wolff and Zimmer, Architects, Portland, OR, 1954-1966; Partner, Wolff, Zimmer, Gunsul, Frasca, Ritter, Architects, Portland, OR, 1966-; Partner, Zimmer Gunsul Frasca Partnership, Architects, Portland, OR, ; offices were opened later in Seattle, WA, and Los Angeles, CA.

Visiting Professor, University of Oregon, School of Architects, 1964-1966;

Zimmer joined the American Institute of Architects in 1952; Board Member, American Institute of Architects, Portland Chapter, 1962-1963, 1966; Vice-President, American Institute of Architects, Portland Chapter, 1964; President, American Institute of Architects, Portland Chapter, 1965; Member, American Institute of Architects, (national organization) Architecture for Community and Industry Committee, 1969-1970; in 1970, Zimmer was a Registered Architect in the states of CA, OR and WA; Zimmer also had NCARB Certification in 1970; Zimmer actively participated on design stages of the Seattle Central Library Project;

Fellow, American Institute of Architects, 1968;