Born in Glencoe, Illinois, Flanders began his training in architecture in 1866 as an 18-year-old apprentice to Augustus Bauer. After a year or two, he joined the firm of Theodore Watskier, and shortly after that, William W. Boyington (designer of Chicago’s iconic Water Tower). Flanders finished his training in the office of Adler and Burling. In 1874, he formed a partnership with Charles Furst. The partnership lasted until 1878, at which time Flanders went into practice alone. In 1886, he and William Carbys Zimmerman formed Flanders and Zimmerman. After 1896, Flanders practiced alone, or with his son, K.F. Flanders.
Flanders served as Architect to the Chicago Board of Education from January 1884 through December 1888, and again from December 1890 through January 1893. In all, Flanders designed more than 50 new schools, including an addition to the old West Division High School, which no longer exists. Among his extant schools are: Thomas Jefferson Elementary (1884), Edward Everett Elementary (1891), Ravenswood Elementary (1892) Louis Nettelhorst Elementary (1892) and William H. Ray Elementary (originally Hyde Park High School, 1893), as well as numerous additions to older schoolhouses.
Flanders became a Fellow of the American Institute of Architects in 1889. During his partnership with Zimmerman, Flanders was especially known for producing elegant mansions in Chicago. Existing examples include the Romanesque style Clarence A. Knight House on South Calumet Avenue, the William O’Brien House on West Arlington Place, and the Gustavas F. Swift House on South Ellis Avenue.