The American Hydtotech project profile (see below) states, “A major design goal for the library was to minimize the impact on the environment through the use of sustainable building materials and systems. Towards this goal, designers decided upon an extensive Garden Roof?, with a 4-inch soil mix and low-growing hardy plants to create a vegetated rooftop that can hold up to the harsh environment without using irrigation. Thanks to the relatively low weight of Hydrotech’s Garden Roof Assembly, no additional roof support was necessary. The Garden Roof Assembly incorporates Monolithic Membrane 6125?-EV waterproofing, a high performance hot-applied rubberized asphalt, together with drainage/water retention elements, root barrier, insulation, and an engineered lightweight growing medium. The assembly?s unique Floradrain? component, made of 100 percent recycled polyethylene, allows for moisture retention within the shallow soil profile while also providing for proper drainage of excess water.

“Keeping with the building’s sustainability goals, Oak Park Library’s Garden Roof requires minimal maintenance, generates energy efficiency benefits, will extend the longevity of the roof’s waterproofing membrane, and reduces annual stormwater runoff by an estimated 50 to 75 percent. The roof will also contribute to better air quality in this architecturally historic neighborhood.”