During a design team meeting for VanDusen Botanical Garden’s Visitor Centre in Vancouver, British Columbia, Canada, serendipity struck when the landscape architect and project designer both arrived with the same image from an early 1900s book of local plants: a native orchid.

According to Jim Huffman, associate principal at Perkins+Will’s Vancouver office and design principal on the project, the moment represented a turning point in the design. “We had the idea of a petal in mind but we were letting the design evolve naturally,” he recalls. “When we saw the perfectly overlapping leaves in the orchid’s image, we knew it was the right form.”

The flower’s profile also gave physical expression to an ambitious goal: to meet the Living Building Challenge (LBC). The LBC uses flower petals to define seven performance areas of site, water, energy, health, materials, equity, and beauty. Designed to be net-zero energy and net-zero water, as well as carbon neutral, the 19,000-square-foot facility is pursuing LEED Platinum certification as well.

“Botanical gardens have been about plant conservation and the promotion of biodiversity,” says Harry Jongerden, garden director at VanDusen. “Now we need to advocate for a more sustainable lifestyle. If we aren’t promoting the greenest technologies, we are failing at our mission.”

The center both looks and functions like a plant. Simple, natural materials give strong form to the structure. The east side is made of rammed earth and concrete walls, and the floors are polished concrete. The majority of the garden’s beauty, as well as its lakes, lie to the west, so the architects oriented the building to take advantage of the views with a window wall and added an overhang—extending up to 12 feet in some areas—to mitigate heat gain. The roof is a series of six petals composed of prefabricated wood panels made with FSC-certified glulam beams, joists, and plywood decking, and all services, such as insulation, ceiling materials, electrical fixtures, and sprinklers, were built into the components to ease construction of the roof, which was assembled in winter.

Adhering to the LBC’s mandate of avoiding a prohibited “red list” of materials required diligence and innovation. Rather than use red-listed perforated vinyl tubing for footing drainage, Perkins+Will had the contractor drill thousands of holes in acrylonitrile, butadiene, and styrene plastic tubing instead.

A 45-foot-tall glass atrium includes a solar chimney composed of windows with automatic sensors and a sculptural aluminum heat sink. The unique shape and colors take advantage of the sun’s orientation. The sun shines through the atrium, heats the aluminum heat sink, and draws air up, cooling the lower section of the building through convection. The designers perforated the aluminum with 1/8-inch holes to create more surface area and transfer the energy back to the air as it runs past. When the windows open, the perforations allow for cross ventilation.

The team strategically positioned 400 solar-hot-water tubes on the north end of the building’s roof and on an adjacent existing building to avoid tree shade. The tubes collect the sun’s heat and store it in water that serves the building’s heating system. The system, in turn, relies on a radiant heating system in the concrete slab floors and forced hot air at the perimeter. Some of the solar hot water heats the radiant heating system’s hydronic fluid. The surplus is directed into 52 boreholes, 200 feet deep, which are placed in a random pattern around the building. Stored at approximately 20 C (68 F), this water helps preheat the needed perimeter hot air in winter and prechill it in the summer.

To achieve net-zero energy, the visitor center swaps excess hot water from the solar tubes for electricity generated in a newly upgraded HVAC system that is housed in a connecting building. The system’s largest electric load is a café for the new building. Since the center has more solar-hot-water tubes than it needs, the center trades heat with an existing restaurant in return for electricity. This allows the project to create all of its energy on site.

Visible photovoltaic panels in the parking lot near the entry provide 11 kilowatts of electricity, which is approximately 20 to 25 percent of the center’s electrical energy needs. Thanks to daylight streaming in from the atrium and window wall, combined with LED lighting, the lighting system’s electric load remains low.

Atop the structure, four of the roof’s petals are vegetated. The two remaining petals are covered with standard roofing membrane; one holds the solar-hot-water tubes, and the other is inverted so that it can collect water and divert it into a 79,250-gallon cistern beneath the building. This graywater is filtered and used in toilets and urinals. Blackwater from toilets and urinals is reclaimed and sent to a bioreactor for treatment, then directed to a percolation field and returned to the surrounding gardens. Excess water from all of the roof petals is collected in a second cistern and conveyed into a drywell. One petal delicately descends to the ground, providing an easy pathway up for small creatures.

“The slope gives animals access to the top so they can deposit seeds there. In this way, the roof will grow and evolve on its own,” Huffman explains.

Educating those inside the center on the correct material selections and resource use to maintain sustainable operations is an ongoing process. “We have room for lectures and symposia, wedding receptions, and a café,” Jongerden says. “We need to generate revenue, but it’s a huge learning curve for our booking staff and renters to ensure responsible use of the building.”

ECO-STRUCTUREcontributing editor KJ Fields writes about sustainability and design from Portland, Ore.