Assembling a 197,000-square-foot rooftop to accommodate a living tapestry of native plant species is challenging enough. Add to that the technical problems posed by the roof's extreme dips and slopes. How to keep the plants and soil from sliding off? Rana Creek, who worked with Piano to design the roof, developed and patented a solution called the BioTray®. They used 50,000 porous, biodegradable trays made from tree sap and coconut husks as containers for the vegetation. These trays line the rooftop like tile, yet enable the roots to grow and interlock, binding the trays together like patchwork.

The Living Roof´s 1.7 million native plants were specially chosen to flourish in Golden Gate Park´s climate. After experimenting with thirty native species, the finalists were all able to self-propagate. They will thrive with little water, resist the salt spray from ocean air, and tolerate wind. The roof will provide habitat for a wide variety of wildlife. A future project will seek to introduce the endangered San Bruno elfin butterfly and the Bay checkerspot butterfly to this new habitat.