Unraveling the backstory of an architecturally mysterious holdout house on East 75th Street

Despite all the recent construction keeping the avenues of Lenox Hill clanking and clattering, this slice of the Upper East Side still has plenty of quiet side streets with unusual low-rise gems. The squat little charmer at 434A East 75th Street, dwarfed by its tidy tenement neighbors on an ordinary stretch between York and First Avenue, is one of them. It’s an architectural mishmash, with a cast-iron facade topped with brick and few ornamental motifs except the rosettes on the columns. An Instagram post from Nolita Architectural Review describes the facade as “an odd mix of Greek Revival (coming from the cast iron bulkhead and column) as well as Art Nouveau (from the wrought iron window bars), and with a bit of Art Deco (from the lintel).” Despite the many intersecting design styles, I still wanted get a sense of when this strange building made its debut and for what purpose. I started with a recent Corcoran listing, which describes 434A—or 434 1/2, as it’s also known—as a…