Upon his return from military duty, Zehnder attended graduate school at the Rhode Island School of Design (RISD), earning a degree in industrial design in 1956. The following year, Zehnder visited Truro to help a friend build a house there and he subsequently relocated to the Outer Cape, settling in Wellfleet (Bailey and McMahon 2006; Bragg 2010). In 1959, Zehnder established a design/build practice with fellow RISD graduate Alan P. Dodge who had moved to Provincetown to paint in the dunes. The same year, Zehnder and Dodge volunteered with a group of about 12 local carpenters in a project to provide the dune poet Harry Kemp with his own living quarters (Provincetown Advocate 1959). Zehnder subsequently designed and built at least 40 houses, additions, and renovations between 1958 and his death in 1985. Dodge opened his own firm in Wellfleet in 1970 to pursue ideas for modular housing.
Zehnder completed more design commissions for Modem style residences on Outer Cape Cod than any other architect. He completed around 40 known residential commissions including the Zehnder/Rose ("Shoebox House" 1957), Zehnder/Richter (1957), Rault (ca. 1958), Franklin (1960), McMahon (1966), Glass (ca. 1970), Kugel (1970), Spitz (1974), Levin/Flaxman (ca. 1975), Goldman (1975-1977), and Baltzell (date unknown) houses; Frambolutti House and Studio (ca. 1965); and Simon House Addition (date unknown) in Wellfleet; the Katz House (ca. 1957), Elliot/Cornelia (1959), Francis (1960), Sprague (1962-1963), Dukess (1963), Becker (1963), Hopkins 1/Nenner (ca. 1965), Thron/Epstien (1965), Mack (1965), Cohen (1966), Bulowa (1967-1970), Topkis/Critchley (1968), Corey (1968-1969), Simon (1969-1970), Paul (1975-1976), Hopkins 2 (1976), Broedur (1977), Pasenen (1981), Wenders (1984), and Yeaston (date unknown) houses; Peretz (1958) and Sass houses and studios (1963/1976); Rothschild Studio (ca. 1983); and Edward Hopper House remodel (ca. 1978) in Truro; and the Wurtman House (1984-1985) in Provincetown. All of the houses display Zehnder's experimentation with architectural geometries and incorporation of elements intended to highlight or complement the surrounding landscape. http://www.nps.gov/nr/feature/places/pdfs/14000019.pdf (pages 8-9)