2020 Pinnacle Award - The Floating Stair
No greater compliment of a material is possible than when stone is selected for a historic property renovation within a home rich in tradition and with a celebrated past. This new feature stair addition to a private residence in Toronto, Canada, has an equally compelling story to tell.
Originally envisioned as a wall-supported, cantilevered stone stair, the owner boldly accepted a unique solution for their showpiece element. The 19-tread stair would be designed with 550 lb. solid stone treads, and fully
liberated from traditional supports and the adjacent rubble wall. To say, “it would float” is not an exaggeration. The stair would be designed as a monolithic beam spanning 16.5 feet, 10 feet high and 41 inches wide. Aesthetically bold, with a reduced tone from
pure black, the basalt stone was the perfect contrast for the white modern interior of the home. The 3-1/2" tension cables played the most important role by resisting the large bending moment generated by the stone load and stair geometry. Fabrication required precise coordination and care to ensure perfect alignment of the interlocking key, and the corresponding cable holes.
The fabrication challenge was achieving the highest level of accuracy in notching, coring, and replicating each tread identically. Expert precision and skill were key to nesting each tread in sequence and simultaneously with the strands. Meticulous alignment and exacting tolerance assured the true performance and aesthetics were delivered. Hydraulic post-tensioning pulled each cable to 120 kiloNewtons or 27,000 lbs, infusing strength and structural integrity. Removing the temporary support and testing was the last critical step—it was the first time the stone stair would be self-supporting.
The “floating” stair is an ultimate achievement and example of innovation, material strength, fabrication quality, installation precision, and expert coordination. A perfect final chapter to a historical journey and modern ode to stone as structure.