Hornig's art considers the built environment and incorporates everyday architectural elements like doors, walls, and windows, as well as industrial materials such as concrete. These appear in both sculpture and site-specific installations. One 2002 sculptural work, Balcony, installed a full stucco balcony – complete with a drying towel – floating above the floor in a gallery. In a 2005 Lisbon exhibition, Hornig created a “stone” wall out of newspaper and glue, extending along and reflecting in a glass gallery wall of windows. One major site-specific work is the Glass Façade Project, or Das Glasfassaden-Projekt, which in 2005 provided a large installation for an elementary school building at Pfeuferstraße 1, in Munich's Sendling district. 

In certain works that incorporate architectural elements, she simplifies and omits details like door handles and adjusts an item's scale in order to transform a recognizable object into a sculpture