In KieranTimberlake's extensive survey of roof gardens, it identified species that were planned, had thrived, or were rogue (l to r, respectively): prairie dropseed (Sporobulis heterolepsis); two-row stonecrop (Sedum spurium fuldaglut); moss pink, pink phlox (Phlox subulata) Credit: Bruce Peterson
The jury highlighted two innovative aspects of the study: its comparative method and its ecological thesis. In 2011 and 2012, Kieran Timberlake surveyed six of its completed green roofs, ranging in area from 1,744 to 10,000 square feet, and designed between 2003 and 2011. Using the Relevé vegetation survey method and the Braun-Blanquet abundance scale to quantify its findings, Kieran Timberlake assessed the roofs’ vegetative cover, species richness, and species diversity in 2-meter-square sections. The researchers also interviewed facilities and grounds maintenance personnel at each site. Juror Bill Zahner praised the study’s “way of collecting the data needed rather than saying, ‘Well, let’s just put seeds down and keep our fingers crossed.’ ” Juror Jing Liu agreed: “What they’re doing is different. The research is to study the long-term dynamics of green roofs.”
The resulting report confirms that roof ecologies are indeed dynamic and that changes will occur spatially and over time from the original planting design. More importantly, it details the nature of those changes, and raises questions about what the changes might indicate for long-term resiliency. In many of the case studies, the prevalent species observed on the roofs in 2012 that were part of the initial planting design were accompanied by dozens of new or “emergent” species. Artemisia (commonly known as mugwort) at the Yale Sculpture Building and Melilotus (or sweet clover) at Cornell University’s Alice H. Cook House independently found their way to roof tops, took root, and eventually made themselves at home in the roofscape design. Roof biodiversity often increased, although the report cautions that the results of any single survey could be deceptive: “What appears to be major shifts in species composition may in fact be short-term fluctuations or cycles caused by unpredictable changes in experienced climate and environmental conditions.”
While the report rigorously maps the distance between design intent and material outcomes, it also sets the stage for even more radical research to be conducted on the interplay between landscape and architecture. Kieran Timberlake envisions deploying sensors on the roof to measure thermal and moisture conditions in relation to the building’s internal climate and energy consumption. The report also suggests that architecture “is responsible for the … vegetative dynamics and ultimate performance of the roof.” On the roof of a dining hall at Middlebury College, for example, the otherwise feeble grasses and forbs become lush and verdant around the skylight cones, whose shade presumably helps the soil retain moisture. “Architectural design creates microclimates across a roof, determining availability of sunlight, water, and nutrients,” the report states.
Kieran Timberlake is already putting its newfound knowledge to use on the forthcoming Penn State Center for Building Energy Education and Innovation at the Philadelphia Navy Yard, which itself will serve as an ongoing laboratory and teaching center for scientists, students, and professionals interested in eco-effective architecture. The firm has developed a proposal to create a green roof test bed on this building; currently, it is in the process of raising funds.
But documenting the consequences of a designed green roof subjected to unforeseeable or uncontrollable environmental forces has wider implications for architecture in general, juror Jing Liu said. “If you think of the green roof as an ecological system, you can have architecture as an ecological system,” she said.
In the messiness of the real world, architecture depends on dynamic variables. Buildings are never really complete. Rather, they are subject to the vicissitudes of client maintenance regimes, the inconsistencies of occupant behavior, and the unpredictability of weather. That is why post-occupancy studies—of both indoor and outdoor environments—must be as meticulous as they are fearless.
Project Credits
Project Green Roof Vegetation Study
Design Firm KieranTimberlake, Philadelphia
Project Team Roderick Bates, Stephanie Carlisle, Billie Faircloth, AIA, Stephen Kieran, FAIA, Taylor Medlin, Assoc. AIA, Max Piana, James Timberlake, FAIA, Ryan Welch
In 2005, when Kieran Timberlake planned the green roof of Cornell University’s Carl L. Becker House, in Ithaca, N.Y., the rigorous planting plan comprised three types of succulents (two-row stonecrop, tasteless stonecrop, and houseleeks), combined with strips of prairie dropseed. When Kieran Timberlake surveyed the roof in 2012, the vegetation was healthy and full, but there were a few surprises—54 of them, in fact. That is the number of new plant species that had taken root over the years.
An aerial view of Cornell campus dormitories shows Kieran Timberlake's green roofs outlined in white; the Carl L. Becker House is at the right side of this image. Credit: Kieran Timberlake
According to KieranTimberlake's study, the most biodiversity was found in the Becker House's southernmost bay, where shading along the adjacent building edge minimized the effects of record droughts.
Various poplar species were found on the Becker House roof, despite not appearing in the original roof planting plan.
Credit: Kieran Timberlake
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