http://article.homebydesign.com/pages/article/HBD_APR_14_05/255186/index.html

Construction on this modern New York City apartment began by completely gutting a circa-1870, five-story building. Where do you start a design when all you have is an empty shell? Asifa Tirmizi, cofounder and principal of Tirmizi Campbell—a New York City-based architecture and design firm—was hired by the developers of the property to answer that question.
“The clients wanted the best value for the property,” says Tirmizi. “In this location, larger units are more desirable. We knew full-floor residences would be the best option.” Typical for the neighborhood, the first floor remained commercial space, but the other four floors, plus the rooftop addition, would each become residential units. “We came up with the idea of doing a penthouse duplex,” says Tirmizi. “The fifth floor and new sixth floor combine to create larger units.”

Before the project could begin in earnest, a few things required fixing. There was a lot of water in the soil underneath the building and it was compromising the structure. “The building leaned about eighteen inches and was sinking into the ground, which was one of the main reasons why we had to gut the structure.”
In New York City, the Landmarks Preservation Commission identifies city landmarks and regulates changes to designated buildings. Tirmizi Campbell worked with the commission on restoring the brownstone façade and determining what color it should be. The cast iron roofline was also kept. The front windows retained wooden frames, and the back, steel windows were refurbished and reinstalled. Other challenges included an elevator shaft that took up one row of the front windows. The shaft was moved toward the center of the building to free up the window and allow more light into the units. A new core stairwell was added, but because most people use the elevator, the stairwell was narrowed to conserve space. A mesh stainless-steel screen decorates the lobby stairwell and points the way to the new elevator. And porcelain floor tile shines with a metallic texture that mimics the look of the screen.
During the gut, all timber inside was removed and replaced with a steel structure. But the wood did not go to waste. Instead, the team shipped the beams to a Wisconsin mill where the timber was machined into planks that were then used as flooring in each of the residences. They were careful to maintain many of the original materials in one way or another, including brick. Tirmizi speculates that the building next door was likely an original sister building to the structure. “I think the two were connected inside when they were built,” she says. “There is an original archway on the party wall between the two buildings. As part of our design, we kept the brick in the units because you could see that hint of an outline.”

The fifth floor plus the new rooftop floor combine to make penthouse suites. Because the added story is set back, the design was able to incorporate outdoor terraces. New steel windows that match the existing windows elsewhere in the building were added to bring the outdoors in. The second level of the penthouse contains the master bedroom, bath, and bonus room, and an open stairwell comprised of steel and glass connects the two floors. “We added skylights to draw in natural light. The stair treads also use the machined original timber,” explains Tirmizi.
The main floor of the penthouse includes a living room and kitchen. The chef-quality kitchen features marble counters atop the walnut island. White cabinets pair with steel appliances, hardware, and countertop edge. The dark floor grounds the otherwise airy space, and the arch of the front windows adds delicate curves to balance the sleek, modern finishes. Similar finishes are found in the full-floor residences on the second, third, and fourth floors. Glass tiles add a sparkle to the kitchen backsplash, and every inch of space is used to its maximum potential.