It was state-of-the-art green architecture before the term was coined: a 325-unit luxury apartment building across from Manhattan’s Central Park occupying less than half of its site and punched with planters meant to extend the foliage of the park into the high-density development. Completed in 1940 by Albert Mayer and Julian Whittlesey—known for Modern, middle-class apartments that self-consciously vied with the emergence of suburban housing—240 Central Park South featured two towers (the larger one arranged in a horseshoe plan to maximize airflow and views), cantilevered balconies, and generous steel casement windows to reinforce a connection to the landscaped pathways, fields, and ponds across the street.

Over the years, everyone from Lewis Mumford to Robert Stern had praised the building as one of the period’s best examples of high-density housing [record, January 1941, page 68]. In 2002—a year before the competition to renovate Edward Durell Stone’s 2 Columbus Circle made the area a preservationist battleground—it was designated a New York City landmark. Today, 240 Central Park South is the only fully restored landmark on Columbus Circle, and with the help of an artfully landscaped green roof by Balmori Associates and some loving updates by architect Douglas J. Lister, its ideas remain as current as when it was built.

When Lister was hired in 2001, the yellowish-orange brick facade had been badly discolored by previous waterproofing efforts, and he quietly began working with the original manufacturer, Belden Brick, to match the former bright hues of the brick. They spent a year calibrating current gas-fired technologies to allow for the color variations that coal-fired factories once produced, eventually reskinning much of the towers’ main facades. Lister also had to upgrade electrical service to the apartments to accommodate today’s IT needs, running new lines through hallways and decorating them with historic Art Deco carpet patterns. On the street level, Bronx-based Diversified Glass replaced the custom-fabricated curving storefronts projecting onto Broadway with a thicker, more resilient black spandrel glass and substituted white LEDs above the bronze sign-bands for the original neon tubes.

But the biggest chance for a contemporary upgrade was on the ground-floor rooftops, where gigantic planters above the storefronts expressed the original marketing motto of the building, “Where the Park is Part of the Plan.” The roof was engineered to support an ample load of 150 pounds per square foot—four to six times the strength required for most green-roof installations—but over the years, ginkgo trees in the planters had grown to a height of 30 feet and overwhelmed the structure. The repair became an opportunity to introduce a true green-roof system that would absorb rainwater, reduce heat, and provide an aesthetic boost to residents.

Balmori composed a three-dimensional rolling landscape of barbary, spirea, and slate quarried upstate, using polystyrene foam underneath the drainage mat and soil layer to vary its slope. The rooftop is not accessible to residents, but from the towers it appears as gently curling bands of green, purple, and gray that form continuous swaths across several levels of the building and extend into the courtyard. In place of the hardy ginkgoes, cherry trees in the curved bastions above the storefronts connect the rooftop landscape to the street, supplemented by a garden at the entrance featuring red and Japanese maples.

Preserving the building while reconciling it with contemporary standards is an ongoing project: Lister is currently studying how to improve its mechanical systems to reduce energy consumption. The owners also plan to eventually replace the steel casement windows with better-insulated replicas, which would vastly improve the building’s efficiency—a process delayed by the need to do in-frame rather than the more ideal brick-to-brick installation, difficult when a building is occupied. For now, its restoration is a great reference point for condo designers and advocates of sustainability alike, currently squaring off over what architecture should look like in a period of economic retrenchment.