Sweltering temperatures and lush tropical rainforests are not characteristics that commonly come to mind when thinking of Winnipeg, Manitoba, one of Canada’s coldest cities. But they are exactly what can be found when meandering through The Leaf, a new landmark in Winnipeg’s sprawling 450-hectare Assiniboine Park. An integral part of an overall redevelopment plan for the park that has been underway for close to 15 years, this addition comprises four separate yet interconnected botanical biomes home to hundreds of diverse plant species, all under one spectacular spiralling roof.

Built to replace the site’s original conservatory, which dated back to 1914 and hadn’t been upgraded in decades, The Leaf biodiversity gardens were designed by KPMB (in close partnership with Architecture49, Blackwell Structural Engineers and HTFC Planning & Design). The firm was intent on delivering something extraordinary. “It could not be a ‘normal’ greenhouse,” says architect and partner Mitchell Hall. “We wanted to create a transcendent experience, one that centres nature and sustainability and is welcoming to everyone.”

To make good on this promise, the designers looked to the natural world for inspiration, specifically the Fibonacci sequence. This led to the formation of a glass-wrapped organic structure with a fantastical roof that mimics the spiral net of a nautilus shell or sunflower. While glass was an obvious consideration for the greenhouse roof as well, it had its limitations. “It’s incredibly heavy and would have resulted in big beams that would cast structural shadows,” says Hall. “We wanted to minimize shadows and maximize sunlight.” After also factoring in the extreme 80-degree temperature fluctuations that the region undergoes throughout the year — and through consultation with climate engineers from German firm Transsolar — it was decided that ethylene tetrafluoroethylene (ETFE) was the most efficient and resilient material to work with.

Supported by a cable net system, the building’s ethylene tetrafluoroethylene roof delivers the transparency of glass but with far better insulation.

To that end, a 33-metre-tall steel diagrid was erected to support three layers of ETFE; this created a quilt-like expanse where the individual “cushions” are continuously filled with air to optimize solar gain and maintain consistent thermal performance for the two climate extremes inside: subtropical and Mediterranean. Integrated mist fans provide both humidification for the plants and comfortable cooling for the people, while a watering system carefully calibrates soil moisture.

All visual noise in the form of mechanical and electrical components was relegated to the apex of the structure, keeping sightlines completely unobstructed and putting the focus entirely on the gardens; natural ventilation and an open-loop geothermal system contribute to the building’s sustainability, while strategically placed light reflectors overhead bounce illumination off the transparent material and can be programmed to mimic moonlight, the northern lights and other natural phenomena.

An 18-metre-tall waterfall designed by landscape architect Dan Euser anchors the greenhouse’s Tropical Biome.

In all, upward of 12,000 flowers, trees and shrubs are spread throughout the Hartley and Heather Richardson Tropical Biome and the Mediterranean Biome (which has already played host to everything from yoga and meditation groups to symphony performances). The other two biomes are the Shirley Richardson Butterfly Garden, which is accessed by an upper-level canopy walk that offers a bird’s-eye view of the verdant gardens below, and the Babs Asper Display House, a gallery for seasonally rotating displays of artistic floral arrangements.

Along with its central greenhouse, The Leaf includes a vegetable garden that grows crops served in an on-site restaurant, plus another 12 hectares of public gardens landscaped by HTFC Planning & Design.

Ultimately a building for the community, The Leaf provides an opportunity for Winnipeg locals and visitors to connect with and experience the natural world in an immersive way and has quickly become the new crown jewel of the parkland.