Tom Woodfin, ASLA Ph.D., Director, Division of Landscape Architecture, University of Oklahoma

Abstract

This presentation updates the evolution of a vegetated roof installed on the National Weather Center in Norman that began as a toy, has become an experiment and is evolving into a replicable example of sustainable design.

The green roof is an experimental system of 1280 square feet of extensive (4” depth) and intensive (8” depth) trays planted with southern Great Plains native grasses and forbs (perennials).  The first three years of experiments were for imported species typical of vegetated roofs elsewhere with minimal watering. The current, second phase of experimentation will validate the viability of Oklahoma native plants in green roof installations. Each tray contains an engineered soil of lightweight expanded clay and organic material mixed according to FLL Guidelines.  The trays are 24” by 48” with small drainage holes across the bottom and lined with filter fabric to prevent the loss of growth media.

The entire experiment is irrigated by drip lines controlled in 8 different valves by an automated controller. Four zones (20 SF each) of extensive and four zones (20 SF each) of intensive trays receive differential watering based upon weather conditions and experimental intent.  The first phase of the experiment was installed by an interdisciplinary team from Architecture, Meteorology and Landscape Architecture from the University of Oklahoma and Biological and Agricultural Engineering at Oklahoma State.  Experimental results were collected for 2 ½ years.  The second phase began in fall, 2012 and is on-going following the complete replacement of the original growth media and planting of native species by both seeding and plugs. Eight species of native grasses and eight forbs are planted in forty single-species and mixed-species trays.  Each species is planted in two extensive and two intensive trays for a total of 32 square feet per species. This spring another 320 SF of extensive and intensive trays are being planted in nectar and pollinator plant species for determining whether apiary habitat is possible in the sixth-floor rooftop situation.  We are also becoming participants in a comprehensive green roof plant trial organized by R. Sutton, University of Nebraska, Lincoln.

The potential for southern Great Plains grasses and forbs to provide avian and insect habitat as well an aesthetically-attractive vegetated roof will be described and assessed in the presentation.  The intersection of experimentation and native context is revealed on the rooftop of the national center for analysis and prediction of severe weather.