The Phillips Eco-Enterprise Center (PEEC) in Minneapolis, Minnesota was constructed to serve as a model for comprehensive sustainable green building design. The PEEC’s 4,000 sq.ft. extensive green roof provides the opportunity to both demonstrate and research the benefits of green roofs including effects of the green roof on stormwater runoff, lifespan of roofing membrane, and temperature directly above the roof. The project also monitors establishment rate and survival of 18 native and 11 European green roof species in a Minnesota extensive green roof environment. The green roof’s deck and seating area, constructed from recycled plastic, provide open space accessible to employees and visitors to the building. The roof was also designed to draw public attention from the adjacent elevated light rail transit line as well as provide educational opportunities.

The design concept for the PEEC green roof blends 40 years of European green roof technology with more than 5,000 years of bedrock bluff prairie evolution to develop living, breathing buildings for Minnesota. Maximizing regional identity as well as plant and animal biodiversity while also minimizing maintenance requirements, a local native plant community with growing conditions similar to green roofs, the Minnesota Bedrock Bluff Prairie, was used as a template to inform planting design. Bedrock bluff prairies are similar to many extensive green roofs in that they have shallow soil profiles and are exposed to considerable heat, drought, and wind. Examples of characteristics that help bedrock bluff prairie plants survive such harsh conditions include: thickened cuticles, hirsute stems and leaves, highly reflective surfaces, fine or narrow leaves, sticky surfaces that can hold onto water, leathery rough leaf textures that reduce the speed of wind traveling over leaves, and water storage cells. These characteristics were also thought to help plants thrive on the PEEC green roof. As high places of prospect with considerable exposure to sun and wind, the bedrock bluff prairie also fits conceptually and experientially as a metaphor for green roofs.

The PEEC planting design called for traditional European green roof plants planted in swale- like depressions with 2” of growing medium oriented in the four cardinal directions. Bedrock bluff plants native to Minnesota, planted in 2”-6” of growing medium, are conceptually emerging out of the European green roof technology foundation developed and refined over the past 40 years. In this way, the design concept reflects use of nature’s template (biomimicry) to inform building design and adapt German technology to Minnesota. 

As the number of bedrock bluff prairies found on the Mississippi River Bluffs has greatly decreased, the PEEC green roof aims to provide an analog of this lost habitat within the Mississippi River watershed.

The roof design does not include an irrigation system. Sprinklers were used during the initial plant establishment period. Maintenance requirements include weeding and watering only during periods of extreme drought. Construction costs were $21.55 per sq.ft. with a project total of $86,200.

Accessible to the public and also visible from the adjacent elevated light rail transit line, the planting design targets both close-up viewing as well as quick glances from a distance. The orientation of the European species in the geometry of the 4 cardinal directions provides prompts for guides leading tours of the green roof to begin their presentations beginning with the relationship of the green roof to its context within its community. Wave-like groupings of one wildflower and one grass species in each group of native bedrock bluff prairie plants create concentrated masses of color and grasses waving in the wind, offering bold, dynamic and ever-changing views. 

This green roof provides an excellent opportunity to educate the public about the many benefits of green roofs through both its high visibility and well-conceived design.