Nestled in historic Sag Harbor on Long Island’s South Fork, this private residence blends coastal elegance with timeless craftsmanship. At its heart is a three-flight stair clad entirely in Danby Fantastico marble—an architectural centerpiece that transforms vertical circulation into a sculptural experience of light, form, and materiality.

Selected for its dramatic veining and soft luminosity, the honed and sealed marble elevates each of the stair’s 50 treads—spanning nearly 46 feet vertically—into an expression of floating elegance. Each 4′-9″-wide tread weighs 770 lbs and was precision-modeled to house complex features: four post-tensioning (PT) cable bores, a recessed LED soffit channel, and an alcove for a concealed aluminum shoe anchoring the glass guardrail. Smooth radiused transitions along the soffit and risers maintain structural integrity while showcasing the stone’s natural grace.

Flights 1 and 2 are reinforced with 12.9 mm PT cables, while Flight 3 employs higher-strength 15.7 mm cables. Top and bottom treads discreetly encase the custom steel anchorages that tie the stair into the as-built framing, allow access for cable jacking, and remain fully hidden within the marble envelope.

Installation followed a carefully sequenced process: anchorage hardware fixed to the structure, treads bedded in mortar, cables threaded and tensioned with hydraulic jacks, then grouted in place. Final trades added the integrated lighting and glass guards, completing the stair’s transformation from raw material to refined form.

This Danby Fantastico stair is a striking example of craftsmanship and innovation—where precise geometry, concealed engineering, and the beauty of natural stone come together to create a truly unique architectural feature.