The primary features of each plant were the design drivers, Alvord observes. For example, a grass’ height or plume and sedums’ color changes during the growing season helped determine where plants were placed.“ We didn’t spend a lot of time trying to design the plant palette so certain areas were blooming at one time or another,” Alvord says. “Instead, we looked for the right mix of plant material that could be sustained on a roof and would provide some visual interest in terms of height and color.”
The trays of the third green roof only contained soil so students could plant those trays themselves.
The reflective roof membrane and modular green-roof trays are independent of each other in installation and warranty. However, the green-roof manufacturer suggested a slip sheet be installed before the trays go down. The slip sheet essentially provides another layer of protection over the primary roof. The pre-vegetated modules were shipped to the building site and installed in the lay-out Alvord and his team specified. Roof drains are accounted for in the layout and placement of the roof trays.
Although the bulk of the plant material had to be regrown after a hard freeze that occurred before the trays could be installed on the biomedical center’s roof, Alvord says there were no delays with the installation. In fact, the overall construction of the building remained on schedule from the time it began design in 2007 and construction in late 2010.
In Alvord’s opinion, installing the first green roofs at the University of Iowa wasn’t the most unique aspect of the project. Instead, he notes capturing rainwater from higher parts of the bio-medical center, storing it in a cistern and then gravity feeding it to the two primary green-roof areas (the areas not cultivated by students) was the most distinctive project aspect. “In our climate, it is generally recommended that you irrigate the green roofs because it helps with the long-term health of the plant material,” Alvord says. “We had always planned on an irrigation system, but the fact that we were able to use recaptured rainwater as opposed to using potable water from the building makes this project pretty special.”
Green Roof Materials
LiveRoof Hybrid Deep System with 6 inches of soil. The pre-vegetated modules were grown by Roof Top Sedums LLC in Davenport, Iowa, and then shipped to the building site and installed by LiveRoof-certified installer Vis Ltd.
Despite the building’s considerable roof area, the design team opted to install the green roofs on lower roof areas upon which building occupants would be looking.
Landscape Architect: Confluence, Cedar Rapids, Iowa
Architect of Record: Rohrbach Associates PC Architects, Iowa City, Iowa
Design Architect: Gwathmey Siegel Kaufman Architects LLC, New York
Modular Green-roof System: LiveRoof Global LLC
Grower: Roof Top Sedums LLC, Davenport, Iowa
LiveRoof-certified Installer: Vis Ltd., Marshalltown, Iowa
General Contractor: Walsh Construction, Chicago
Reflective Membrane Manufacturer: Johns Manville
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