Combining innovative architectural, structural and mechanical solutions in one design, the striking glass envelope of the Grand Théâtre de Québec ensures the long-term sustainability of a central piece in Quebec City’s modern heritage with a building encapsulation that represents a first in North America. By adding a transparent, immaterial and structural layer to the original theatre built in 1971, the building’s two distinguishing components were protected and preserved: its brutalist architecture by Victor Prus and sculptural mural by artist Jordi Bonet. Defined by its prefabricated concrete indoor and outdoor walls, with nearly 60% of its interior covered by the mural, this cherished cultural icon embodies Quebec’s Quiet Revolution with its modernist design and monumental, intertwined sculpted work. The glass casing is a delicate response to a complex problem. Before work began, moisture had caused the concrete panels’ steel anchors to disintegrate, and its crumbling exterior required meticulous interventions. Alterations were then severely limited, as architectural and technical solutions could not hinder building access, and the theatre had to stay open throughout the process; this meant that the construction’s complex interventions could only take place during specific windows of time and noise could not escape during shows or rehearsals. Weather conditions posed another major challenge as the new envelope’s installation was only possible under specific climatic conditions, with the glass needing to be attached to a steel structure that could not be exposed to any significant temperature variation from the moment of its adjustment to the glass’ installation. Using custom-designed construction systems, the delicate steel structure on which the glass rests is the result of intense and sustained teamwork among architects, engineers, construction specialists and manufacturers who designed a revolutionary structure. Shielding the theatre from the elements by creating a secondary, tempered envelope, this combination of steel and glass houses a low-flow heat recovery and thermal mass system, acting as an extension of the original building it protects, using the same finely tuned structural logic and composition. While leaving the building intact and perfectly visible, it amplifies the original building’s morphology, where it revolves at the corners, lifts at the base and fades like a jewel. Conversing delicately with the city, it can appear solid or immaterial depending on the light, blurring the boundaries of the building. Writing a new act for the great theatre and the community, its suspended glass forms its own scenography for a story of renewed life. An envelope closely linked to a work of art, the Grand Théâtre lives on as a cultural hub in the heart of Quebec City, thanks to a preservation which combines sustainability and long-term durability.