About The Green Roof

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Did you know that SIU Carbondale has its own green roof?  Since many SIU students are from urban areas where green roof technology is flourishing, the College of Agriculture and Green Fund decided it was time to have one on campus.

During re-roofing of the Agriculture Building in 2008, a section was designed to support a green roof largely dedicated to research. This roof was installed with the assistance of professional volunteers. Materials were purchased through the SIU green fee fund, College of Agricultural Science and Plant Service Operations support, as part of the landscape horticulture program. Over 150 students, professional volunteers, plant services laborers and faculty installed the green roof system over the week of September 25, 2010, with Professor Karen Midden from Plant, Soil & Agriculture Systems organizing the project.

Green roofs are similar to rooftop gardens and are becoming increasingly popular in urban settings because they help control storm water runoff and resulting water pollution. The roof reduces heating and cooling costs for the Agriculture building while acting as a research tool for graduate and undergraduate students.

This semi-intensive green roof has four sections; a sedum dominated classical European section, a second sedum dominated section with a modern drainage membrane, a research and wildflower meadow section, and a second research and wildflower meadow section.  The sedum dominated classical green roof system has two layers of media, the bottommost is light weight aggregate to function as the drainage layer. 

The two native sections were planted with trialed plants from Intrinsic Perennials of Hebron, IL, and Pizzo Natives of St. Charles, IL. The roof also includes a smaller section filled with native grasses. There is an additional native plant section on the southeast area of the building, with research areas for vegetable research, including lettuce, radishes, and tomatoes.

The green roof consists of these plants, Midwest trading green roof substrate (kiln-expanded aggregate containing perlite), filtration layer, drainage layer, root barrier, waterproof membrane, insulation, and finally the roof deck. The fully saturated roof was designed to weigh twenty-five pounds per square foot. 

A moisture retention fabric was unrolled and cut to size in sheets onto the roof, and is made of a non-biodegradable plastic fabric that can hold more than its weight in water. It serves the purpose of preventing root penetration, and retaining water for the green roof, while dispersing weight on the waterproof membrane.  The drainage layer, sometimes called a water retention membrane, is made of injection molded plastic. This layer is above the root barrier.

The drainage layer is visually similar to egg cartons, with cups that can overlap into each other which coupled with the weight of the above layers, hold the drainage layer in place. After these cups fill with water, the excess drains laterally over a small slope on the roof surface, and then off the roof via drain. The drainage layer prevents saturation beyond an engineered weight.

The plant list for the meadow or wildflower section of the SIU green roof includes 17 plants with the growth forms of grasses, a sedge, flowering plants, and sedum. Grasses include Blue Grama (Bouteloua gracilis), and June Grass (Koeleria cristata).  Flowering plants include Nodding Wild Onion (Allium cernuum), Wild Columbine (Aquilegia canadensis), Heath Aster (Aster ericoides), Harebell (Campanula rotundifolia), Lanceleaf Tickseed (Coreopsis lanceolata), Purple Prairie Clover (Dalea purpurea), Prairie Smoke (Geum triflorum), Cylindrical Blazing Star (Liatris cylindrical), Foxglove Beardtongue (Penstemon digitalis), Pale Beardtongue (Penstemon pallidus), Prairie Cinquefoil (Potentilla arguta), Hairy Wild Petunia (Ruella humilis), and Fame Flower (Talinum calycinum). The sedums on the  roof include; Goldmoss stonecrop (Sedum acre), S. rupestre, S. rupestre ‘Angelina’, Widowscross (S. pulcellum), Helix Sedum (S. sexangulare), Golden Carpet Sedum (S. kamtschaticum), S. album ‘Coral Carpet’, and S. spurium ‘Dragon’s Blood’.  This plant community will respond to its environment to develop its own ecology.