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The defining feature at The Leaf, an innovative horticultural attraction nestled within Assiniboine Park in Winnipeg, is its sprawling curved roof, made of ethylene tetrafluoroethylene (ETFE) for improved thermal performance and sustainability.

As part of Assiniboine Park Conservancy’s extensive redevelopment plan, The Leaf covers 14.2 ha (35 acres) and houses four distinct plant biomes, a butterfly garden, a classroom, a restaurant, and a coffee bar.

Created by KPMB Architects, in collaboration with Architecture49, Blackwell Structural Engineers, and HTFC Planning & Design, The Leaf’s roof draws inspiration from the Fibonacci sequence, seen in nature’s gentle spiral patterns (e.g. sunflowers and nautilus shells). The roof’s intricate cablenet structure cancels out the need for columnar support and provides visitors uninterrupted views inside. It unfurls, resembling a blossoming flower. The cablenet system projects out of a 30-m (100-ft) tall steel tower placed in a diagrad at the centre of the roof’s spiral.

Strategically placed lights and aluminum reflectors at the cablenet system simulate natural phenomena such as moonlight, thunderstorms, and the Northern Lights. The building’s organic, curvilinear form mirrors the complexity of the plant species within The Leaf and the surrounding parkland.

The roof is designed to allow for different levels of solar radiation corresponding to the four distinct plant biomes and the visitor areas within the structure. A frit covers the centrally placed visitor area to minimize solar penetration and heat gain, while the plant biomes are covered with non-fritted roof to allow for maximum solar penetration.

Winnipeg’s extreme climate necessitated these innovative design solutions. The Leaf is one of Canada’s largest ETFE buildings, offering improved thermal performance compared to traditional greenhouse materials. ETFE’s transparency allows ample sunlight while natural ventilation and an open-loop geothermal system to maintain ideal temperatures for the diverse biomes. Mist fans further ensure optimal moisture levels for plants and visitors.

Visitors commence their journey in the Hartley and Heather Richardson Tropical Biome, featuring a meandering pathway and Canada’s tallest indoor waterfall—rising to 18 m (60 ft). The Mediterranean Biome is filled with vibrant colours, textures, and fragrances of plants from around the world. The Babs Asper Display House hosts dynamic floral displays that change seasonally, and the Shirley Richardson Butterfly Garden offers a canopy walkway with panoramic views.

The outdoor gardens, designed by HTFC Planning & Design, extend across 12 ha (30 acres), offering opportunities for community interaction and connection to nature. Six unique areas, including the Indigenous Peoples Garden, Kitchen Garden, Sensory Garden, Performance Garden, Seasonal Garden, and The Grove, enhance the outdoor experience.

“For The Leaf, we wanted to create a transcendent experience that centres nature and sustainability. We wanted to do something innovative, something extraordinary, that could be enjoyed year-round in a city with extreme climates,” says Mitchell Hall, KPMB partner. “The building itself is designed as an ode to the beauty of nature so visitors can feel the respect for the earth and environment from the very first look.”