Lang was a highly respected architect, active in the Denver area from 1885 to 1893. He was known for his love of Victorian lines and unusual finishes, which made him in demand with Denver's new upper class during the height of the Colorado Silver boom. His buildings employ a variety of styles and can be recognized by his use of the Richardsonian Romanesque style, with rusticated stone, turrets, arches, stained glass and gargoyles.
In his brief but prolific career he designed over 250 buildings individually and in partnership with the firm Lang & Pugh. Some of those buildings survive today and are now listed on the National Register of Historic Places, including his most well known project at 1340 Pennsylvania Street in Denver. This house was once owned by the Unsinkable Molly Brown of Titanic fame and is now home to the Molly Brown House Museum.