Green Roofs: Preserving the Future
In the center of Columbus, American Electric Power is taking steps to help protect the environment, reduce waste of natural resources, and put Columbus on the map with other forward thinking places around the world: Stuttgart, Chicago, Pittsburgh, Northern Kentucky, and Chardon, Ohio.
Why a Green Roof?
An extensive green roof stores 75% of rainwater in plants and the soil layer. Twenty-five percent percolates through the vegetation after several hours and releases into storm drains. A green roof reduces peak flow of water during intense downpours; concrete and hard surfaces sluice the water into the drainage systems. The 15,988 square foot AEP Green Roof captures the first inch of rainfall for the building's grey water system (used to flush toilets). Additionally, only recycled water is used for irrigation on the roof; the water is stored in a tank on top of the building.
What are the other benefits?
Thermal insulation. According to Roofscapes Inc., a green roof allows new construction to be designed with smaller HVAC systems, requiring less maintenance. By shielding the surface from harmful UV rays, a green roof reduces the daily expansion/contraction of the roof materials caused by temperature fluctuation. A green roof has the potential to reduce the urban "heat island" effect by adding moisture to the atmosphere, and a roof with 6 inches of sod reduces noise by 50 decibels. Last, but certainly not least, a roof garden provides habitat for birds and insects, as well as native grasses, wildflowers, and endangered indigenous plants.
How is a roof garden different?
Being on top of a building, these landscaping projects require special planning and materials. You don't just dump 6 to 12 inches of heavy topsoil on a roof. An example of growing medium used is a mixture of coarse sand, forest humus, red lava, and other light materials. Depths on the AEP garden are 6, 8, and 12 inches, so the plant materials chosen are those with shallow root systems, such as sedums, small grasses, Dianthus, Saxifraga, Potentilla, and others. The first planting consisted of 24,000 plugs of more than 60 varieties. The deeper soil areas are located over support columns and I-beams, and are planted with grasses and some herbs.
The AEP Rooftop Garden is a valuable project for learning about new ways to conserve energy and natural resources. The garden isn't yet open to the public and, in its first year, is not lush with growth. But strolling over the terracotta red and tan walkway of paver tiles made from recycled automobile tires, the view of the city is magnificent, and will only get better!
All photographs ©2007 Toni Leland
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