PROJECT The Leaf, Assiniboine Park, Winnipeg, Manitoba
ARCHITECTS KPMB Architects in association with Architecture49 with HTFC Planning & Design and Blackwell
TEXT Lawrence Bird
PHOTOS Ema Peter, unless otherwise noted
One of Winnipeg’s most popular parks has become home to an innovative new conservatory. The Leaf, by Toronto’s KPMB Architects in partnership with Winnipeg firms Architecture49 and HTFC Planning & Design, is a building and set of landscapes that are oriented, in every respect, toward the sun. Minimizing structural and mechanical systems, and eschewing glass in favour of an innovative material assembly, the designers have created a complex as light and intricate as the flora and fauna living within it.
Assiniboine Park has been one of Winnipeg’s most prominent green spaces since its creation in 1904. Designed by Frederick Todd, Canada’s first registered landscape architect, the park spoke the language of the Victorian City Beautiful movement: it was expansive, picturesque, and domesticated. One of the gems within this symbol of Empire was the grand Palm House, where exotic plants from around the world were displayed. But times and styles change, and in 1970, Pratt Lindgren Snider Tomcej and Associates’ conservatory entombed and then replaced the Palm House, deploying concrete and brick in service of a sober, sensitive modernism. The Leaf, which replaces the conservatory, speaks a completely different tongue—of biomimetic, biophilic and culturally informed design.
As it is for any plant, sunlight is a driving force for The Leaf. The designers’ intention was to open the roof—and raise the visitor’s eyes—to the sky. To this end, in place of glass the designers selected the more transparent, lighter, and flexible Ethylene Tetrafluoroethylene (ETFE). They worked with Blackwell Structural Engineers to dematerialize the overhead structure. Instead of beams or trusses, a cable net support hangs from a central diagrid mast. Based on a rotational hyperboloid, the net’s anticlastic curvature allows it to be prestressed for rigidity. An array of ETFE pillows—the longest 87 metres in length—flows down the net. In section, these ETFE cushions are triple-ply lenses, with the middle ply perforated to equalize air pressure along the length of each cushion.
To see ETFE deployed at this scale, in a climate similar to Winnipeg’s, design architect Mitchell Hall of KPMB took the team on a field trip to Kazakhstan to study Foster + Partner’s Khan Shatyr Entertainment Center. But a number of design gestures make the Winnipeg design more interesting—and more technically challenging—than the Kazakhstan building. Foster’s roof is radial, elliptical, and symmetrical. In contrast, the Leaf’s cushions flow down in an asymmetrical array. They follow a Fibonacci spiral—a pattern that recurs in many natural forms, from sunflowers to galaxies. As Lee McCormick, architect of record, explains, this beautiful gesture is also site-specific. The highest floor level in the Leaf, housing a butterfly enclosure (one of four interior biomes), corresponds to the top floor of an iconic existing tower near the centre of Assiniboine Park. To accommodate this raised space and provide views to the tower, one edge of the roof was split and lifted; the opposite edge is scalloped. Where the cushions encounter the ground, they fan into two lobes. Architect Mitchell Hall grows bonsais, and likens the nipping and clipping that achieved The Leaf’s form to the trimming a gardener does to perfect their plants.
The twisting design, combined with the 150-millimetre depth of the tensile net that supports it, created an overturning effect at each of the 666 nodes. That challenge was resolved by engineer David Bowick’s asymmetrical node design—a rather intriguing, insectoid form that seems to suit the long, wing-like expanse of the ETFE tubes. Left to itself, the building would, in fact, fly away. Uplift is counteracted by a perimeter ring beam, an immense raft slab, and a hollow-core concrete service block that houses the restaurant, kitchen, office and support spaces.
The diagrid supporting the tent-like roof and walls cleverly integrates structure with electrical and mechanical needs, along with vertical circulation. Luminaires and reflectors are concentrated at the top of the diagrid to avoid blocking sunlight; they bounce light down into the biomes. The light changes to echo the phases of the moon, thunderstorms, and even northern lights. Seven storeys up, a floating catwalk arcs around the diagrid to reach the butterfly enclosure. As they walk this route, visitors pass a laminar waterfall designed by Dan Euser, creator of the September 11 Memorial Fountain in New York City. The journey is reminiscent of canopy walks in rainforests, with the waterfall misting the air. The waterfall also serves a functional purpose: in combination with a fog misting system tucked into the lush landscape at ground level, it helps maintain the relative humidity of the subtropical biome. Another feature of the diagrid is an array of exhaust dampers near the top. Paired with a band of BAS-controlled relief dampers around the skirt of the building, this generates a stack effect that allows for mainly passive ventilation. The system is aided by high-velocity nozzles on the sides of the raised walkway, which actively mix the air as needed.
Mechanical ingenuity continues in the fire suppression system. To avoid overhead obstructions, the designers proposed an alternative solution to the code-mandated sprinklers and smoke baffles. Rather than burning or melting in case of fire, ETFE crinkles and retracts. The designers determined that holes opening in the material, in combination with the stack effect, would ventilate smoke rapidly from the building.
The designers thought of the building as a living organism, its internal environment regulated by mostly natural means. Passive solar heating and an open-loop geothermal system are supplemented by a condensing boiler for peak loads. The geothermal system also heats the root systems of the plants, and the pathways winding between them. LEED certification is currently underway.
Of course, landscape is at the heart of any garden. Landscape architect Monica Giesbrecht and her team at HTFC Planning & Design modelled the interior biomes in clay, feeling there was no substitute for a tactile understanding of space, heights of different levels, and the subtle undulations of the plant beds. The subtropical biome is essentially a single 2,000-square-metre space, but the crafty design winds long paths through it and screens perimeter service corridors behind plantings, transporting visitors to a different clime. The plants that fill the rich, immersive landscapes have exceeded expectations for growth.
A set of new exterior gardens surrounding The Leaf is organized along a strong axis from the park’s southeast corner. Nine distinct outdoor gardens border or intersect the main promenade, while a series of mounds arrayed at irregular intervals to either side of the axis frame strong views to the partially earth-bermed Leaf building. The layout recalls similar axes and mounds created by Indigenous cultures that spanned areas from Manitoba to Central America. While Giesbrecht says that this was not the intention, she does underline that the design and process were intentionally decolonizing.
To develop the Indigenous People’s Garden, in particular, HTFC worked with the father-daughter team of David and Cheyenne Thomas (Anishinaabe), and Mamie Griffith (Dene). The Thomases and Griffith consulted with more than thirty Indigenous groups from Treaty One First Nations (the nations who signed Canada’s first treaty in 1871), Shoal Lake First Nation (from which Winnipeg’s water supply comes), and communities in northern Manitoba. The overwhelming feeling of the Indigenous people consulted was that they didn’t have a place in Assiniboine Park.
Indeed, the park is in Winnipeg’s privileged southwest. But there is soon to be a significant shift in the centre of Indigenous influence in the city. The new gardens’ main axis points directly southeast toward Naawi Oodena, a future 64-acre urban reserve less than a kilometre away. What David Thomas (who is also Planning and Design Manager for Naawi Oodena) says is most satisfying about the new gardens is that they “have created a bridge for use of the park for First Nations communities.”
To create that bridge, Elders encouraged the team to pursue collaborative processes as they designed the gardens. The Indigenous People’s Garden is woven with motifs referring to constellations of stars, seasons, elements, and spirits. These spaces, along with David Thomas’s haunting Corten steel “whispering lodges,” are conceived as living storytelling spaces.
All of the gardens, inside and outside of The Leaf, might be seen as such. They are programmed by the Assiniboine Park Conservancy’s education and engagement team for intergenerational teaching across Winnipeg’s distinct seasons. Visiting groups can appreciate, for example, the technique of espalier—which trains pear and apple trees along a sun-facing masonry wall—and then enjoy the literal fruits of these methods in The Leaf’s restaurant. They can see how the Kitchen Garden is watered entirely from runoff from the 6,500-square-metre roof. Both interior and exterior gardens feature plants that Winnipeggers will recognize as those they saw (and used, and ate) in their home communities, whether boreal or tropical. The gardens are designed to speak to everyone.
Construction was not without challenges. Components were sourced from around the world. Pandemic-related supply chain delays were compounded by the narrow scheduling window imposed by Winnipeg’s climate. The butterflies themselves proved demanding clients; they require specific accommodations in wind speed in order to fly, and specific wavelengths of light to navigate—other wavelengths would render their brilliant colours dull. But such is architecture. As McCormick puts it, designing a building for plants, animals, and humans means three different user groups, often with conflicting needs. He describes the sun as a fourth user: it is the driving factor in this building, as it is for the planet. As he points out, its movement across the sky through the hours and the seasons, and architecture’s adaptation to that movement, create a building whose experience changes profoundly with time. Coming here at night is a completely different experience from coming here during the day, and winter from summer. David Thomas made a similar observation about the exterior gardens: that they transform at night. For him, that is when he can step into the world of dreams called for by the Elders. Gardens always engage time: the organic and magical environment of The Leaf celebrates it.
Lawrence Bird is an architect, city planner and visual artist based in Winnipeg.
CLIENT Assiniboine Park Conservancy, with Corbett Architecture | ARCHITECT TEAM KPMB Architects: Mitchell Hall (FRAIC), Glenn MacMullin, Angela Lim, Robert McKaye, Victor Garzon, Lukas Bergmark, Elizabeth Paden, Richard Mui, Victoria Ngai. Architecture49: Lee McCormick, Sarah Chernis, Michael Conway, Vizmark Evangelista, Philip Harms, Curtis Rehberg, Wayne Brewer, Darren Wigley, Ron Martin | STRUCTURAL Blackwell | MECHANICAL Integral Group | ELECTRICAL SMS Engineering | CIVIL | LANDSCAPE HTFC Planning & Design | INTERIORS KPMB Architects and Architecture49| ENERGY & CLIMATE Transsolar Inc. | ETFE SYSTEMS Vector Foiltec | CIVIL KGS Group | VERTICAL TRANSPORTATION Soberman Engineering | CODE LRI Engineering | LIGHTING Mulvey & Banani International Inc. | INTERPRETATION AND VISITOR EXPERIENCE Lord Cultural Resources | WATER FEATURE DESIGN DEW Inc. | ACOUSTICS Aercoustics Engineering Ltd. | QUANTITY SURVEYOR Altus | CONTRACTOR Bird Construction | AREA 7,840 m2 | BUDGET $130 M | COMPLETION November 2022
ENERGY USE INTENSITY (PROJECTED) 369 kWh/m2/year