The Oaklyn branch of the Vanderburgh Public Library in Evansville, Ind., not only creates a prairie blending into the landscape, it is a prime example of environmental stewardship. The project has been widely honored: It was a winner of the Green Roofs for Healthy Cities North American Green Roofs of Excellence Award, and the American Institute of Architects Indiana Honor Award.
To emulate a mesic meadow prairie ecosystem, characterized by a deep soil profile and perched water table, Roof-scapes Inc. selected an irrigated two-layer Roofmeadow Type IV: Meadow 1 green roof system. Designed to last the life of the building, the 6-inch base layer of granular media and 8-inch upper layer of growth media are under-girded by hot-air welded waterproofing membranes. To support the weight of this intensive green roof system, the architects provided a strong but lightweight concrete/steel composite roof deck.
An Optigrun base trickle irrigation system introduces water at the base of the green roof profile. Water is retained in the vegetated cover through a roof riffle.
This is an extremely efficient method of irrigating the green roof and closely resembles natural conditions associated with the shallow soil over shale bedrock.
To promote drainage, the roof deck pitches uniformly at 3% toward one edge of the building
The building's energy efficiency is enhanced by the impressive lag effects of the super-insulated building envelope: the combined green roof, three subterranean walls, and high-performance glazing. Although the facility is three times larger than the one it replaced, utility costs are comparable.
The LightBridge clerestory that rises above the roof meadow has become a beacon to the community, a metaphor for the mission of the library, visible for miles across the Pigeon Creek Valley.
Vanderburgh Public Library, Evansville, Ind.
Green Roof Installer:
Enviroscapes Inc., Madison, Wis.
Sarnafil Inc., Canton, Mass.
Midland Engineering Co., South Bend, Ind.
Veazey Parrott Durkin & Shoulders, Evansville, Ind.