Creating a Sexy, Sinuous Stair
Rehabs don’t always offer one the type of existing space that allows us to do something truly special, architecturally speaking, but a federal-style row house in Georgetown presented just the right opportunity.
This home already had a half-story elliptical stair in it—a classic design that we wanted to expand and improve upon. We dug down and enlarged the existing space below the stair’s enclosure to create a new stair that would span two stories, going down to a new, principal below-grade floor.
The existing stair was built of wood, and encased in wood-framed walls. Collaborating with Baltimore interior designer Patrick Sutton, we designed a self-supporting stair made of stone, which would surprise and delight the owner and his visitors and also reference the city’s great monuments. Among our direct inspirations were the dazzling twin elliptical staircases in the U.S. Supreme Court building, each climbing five stories on self-supporting marble risers.
We added skilled experts to the design team to accomplish a similar feat in the much tighter space of this Georgetown residence: Structural engineer Chris Cobb of 1200 A.E. Engineers worked closely with us on structuring the stairs. Pyramid Builders was the able general contractor on the fast-tracked job, and Marmi Natural Stone in Atlanta was the specialty contractor that fabricated and installed the actual stair. They were also intimately involved in the evolving design with our office, Patrick Sutton and the rest of the team.
For its construction, Patrick selected SUV-sized blocks of Imperial Danby marble from Danby, Vermont—the same quarry, fittingly, that provided the marble used to build the Jefferson Memorial and other DC monuments.
Unlike a circular stair design, the elliptical geometry posed complicated structural-load design, fabrication and construction challenges. Each of the 27 solid stair treads and risers has different dimensions, so each carries and transfers its unique loads in different ways. Furthermore, the run of the spiral stair is interrupted by a major landing two-thirds of the way up.
To provide the necessary rigid containment for the stair, we replaced the wood-frame enclosure with solid reinforced masonry walls. This wall also provides the outer support for the edges of the stairs—each of which weigh several hundred pounds.
Each marble tread locks into and leans on the one below it for support, and the inside of the stair’s raised, solid-marble stringer creates a self-supporting “spiral arch” braced at each end by rigid, steel landings. For the stair to be successful, almost no movement could be tolerated, so the design and execution had to be precise. It was constructed by Marmi and Pyramid with precision, to tolerances of no more than 1/32 of an inch at any joint.
The process was entirely collaborative; ideas and shop drawings went back and forth between our office, Patrick’s, Chris’, Pyramid’s and Marmi’s. This process included all the design details, including the continuous wrought-iron balustrade and solid-walnut wooden handrail.
The finished result is an ultra-chic space that leads from the home’s main floor to its plush lower level, which Patrick designed as an elegant club for the owner’s many gatherings, both big and small. This jaw-dropping stair no doubt sets the right mood as the owner’s guests descend.