Construction of the Holcim Awards winning net-zero energy greenhouse at Wellesley College, USA was completed in 2019. Sustainable design is at the very core of the structure, form, and system – meeting sustainability metrics as a matter of course and then goes much further to achieve a virtuosity of integration. The Global Flora conservatory at the Margaret C Ferguson Greenhouses will open to the general public when renovation of the Science Center is completed, planned for early 2022. More than 1,000 varieties of plants are housed in the bio-friendly greenhouse – and are showing signs of handling the transition well.

The collection includes relocated plants from the old greenhouses including the iconic 150-year-old Durant camelia, as well as new specimens such as tree ferns that are taking advantage of the soaring 12-meter interior height that would be impossible using conventional construction methods. Global Flora opened for limited hours to members of the College community from September 2019.

Reimagining the Greenhouse

A typical greenhouse is an energy- and water-intensive building. But for this project, Boston-based Kennedy & Violich Architecture (KVA) led a project team that worked to reimagine the structure as a sustainable, net-zero energy building. Together with Wellesley College, they designed a greenhouse that is much more than simply a climate-controlled envelope. It houses a preeminent plant collection, supports an innovative public education curriculum that integrates sciences, humanities, and the arts, and enables studies of plant form adaptations.

“Global Flora will just floor people with diversity of form and texture and color. It’s a cathedral of sorts, a temple of biodiversity,” says Rob Nicholson, Botanical Collections Manager, Wellesley College Botanic Gardens.

“We are going for Living Building Challenge certification,” says Cathy Summa, Associate Provost and Director of the Science Center at Wellesley College. Global Flora must be open for a year to collect data to be eligible for the challenge, administered by the International Living Future Institute. It recognizes buildings that connect occupants to light, air, food, nature, and community; are self-sufficient and remain within the resource limits of their site; and create a positive impact on the human and natural systems that interact with them.

Beauty that’s more than skin deep

The secret is the structure’s ETFE cladding. A thick, translucent plastic, ethylene tetrafluoroethylene (ETFE) is lighter and more flexible than glass. Using it requires much less structural support, which allowed the architects to add more height and volume than the previous greenhouses had. “Nobody anywhere has built a greenhouse of this shape and material,” says Kristina Niovi Jones, Director of the Wellesley College Botanic Gardens. “There’s about half as much steel as there would have been if this were glass.”

The exterior consists of two-layer pillows of ETFE. Each pillow is connected to a compressed air system that blows air in or lets air out, constantly measuring the pressure in that pillow. As atmospheric pressure fluctuates, the pillows respond. The pillows also make a huge difference in insulating the building. Single-layer ETFE doesn’t insulate much, but the envelope of air between the layers is a great buffer for temperature differences. Last winter, the inner layer of ETFE barely felt cold. The strength of the material has also been proven, with the structure easily handling the New England snow load.

Consideration of the plants’ basic needs – water and light – was central to planning the design. The south-facing conservatory is replete with light. A computer-controlled interior shade system mitigates summer glare. Recycled rainwater from the roof of the structure and from the Science Center roof is captured in two massive underground cisterns. The water is then drawn up, filtered, and used for hand-watering the plants as needed. Data from sensors, as well as manual observation by staff, determine which plants need what, and when.

A biological research space of EPIC proportions

Global Flora is intrinsically a research facility. The Exploring Plants in Context (EPIC) platform uses sensors in the soil to continuously gather data about water content, pH, salinity, and more. The data will be available for analysis in interdisciplinary science courses. “We’re monitoring the water and how we water. We’re monitoring the air temperature, humidity, and so forth. We’re monitoring the nutrients in the soil. We’re monitoring everything we possibly can,” says Cathy Summa.

“The new structure provides a place where growing season lasts year-round, Kristina Niovi Jones says, making it ideal for teaching. “The opportunity to study plants, microbes, fish, predator-prey interactions, and things like that in a ‘bubble’ in New England is really cool. We’ll have a lot more ecology going on in here, studying the relationships between things. Because the plants are out of their pots and in the ground, they will be interacting underground, and we’re trying to visualize more about what’s happening underground with the sensors. We’re interested in things like how nutrients are moving through the system, how the water is moving. It’s still a museum of plants, a really amazing collection, but they’re also part of a community that we hope will interact with each other.”

Global Holcim Awards recognition

Global Flora was a finalist in the Global Holcim Awards competition in 2018. In recognition of this achievement, the project’s main authors Sheila Kennedy and Frano Violich of KVA were presented with a finalist’s certificate at the LafargeHolcim Forum 2019 held in Cairo. The project was praised by the Awards jury: Greenhouses stand for challenges posed to the profession of architecture to reduce the means needed for enclosure. The jury greatly valued this project for addressing this history with a reduction not just in material for enclosure; but also in the resources needed for ongoing use.

The project was named US Building of the Week in September 2020 by World Architects.

Credit: This project update was originally published in December 2019 but updated in September 2020 to include new images of the project and further details generously supplied by KVA Architects. Selected text in this article sourced from “The new global flora collection celebrates plant diversity” by Catherine O’Neill Grace, photography by Webb Chappell in Wellesley Magazine, Fall 2019.