Ancient Babylon was graced with a garden estimated to be 400'x 400'. What made this garden so spectacular that it is considered one of the Seven Wonders of the ancient world? It was the first documented green roof in human history – the Hanging Gardens of Babylon.

   The story recounts that King Nebuchadnezzar II built the gardens to cheer up his wife who was homesick and found the landscape of Babylon depressing. Reeds and tar are thought to have been used to waterproof the huge stone terraces on which the gardens sat. Today green roofs are much more than gardens, and technology makes them a viable solution for many commercial buildings.

   Green roofs provide many benefits to both the building owner and the greater community. Their prominence as an important feature in a cityscape is already well established in Europe, and in America these roofs are quickly on the rise.

   One of the largest green roofs in the world is in Deerborn, MI at Ford's Rouge River Truck Plant. The construction of this $3.6 million, ten-point, four-acre roof cost twice that of a conventional roof. Obviously, such a huge investment is economically worthwhile only if there are major benefits.

   One of the major benefits of a green roof is the reduction of storm-water runoff. Many communities in Northeast Ohio face the reality of this issue regularly. As more and more previously open areas are built on or paved, less water is able to soak into the ground. The result is an overloading of storm water systems and flooding in low areas. Ford's River Rouge Plant absorbs four million gallons of storm water per year. With a conventional roof, most of this water would end up in the Rouge River perhaps after wreaking havoc on its way there.

      In urban environments, another sizable benefit of a green roof is the reduced heat-island effect – the six to eight degrees of increase in temperature in urban areas over nearby suburban areas. The dark surfaces of conventional roofs absorb heat. (Think of walking on asphalt in bare feet on a hot summer day. The hot surface makes this an uncomfortable exercise.) It is not unusual for an asphalt roof, an extremely common roof type, to reach 180 degrees – 90 degrees warmer than the air temperature. A green roof can actually be cooler then the surrounding air.

   By making a roof cooler, two important benefits are accomplished. First, the roof membrane will likely last longer. Secondly, the heating and air conditioning costs of the building are reduced. In the summer, the roof is cooler, which results in a lower temperature inside the building. In the winter, the top soil adds the equivalent of supplemental insulation, which reduces heating costs.

   There are two major types of green roofs. In intensive roofs, eight inches to four feet of growing media is applied over the concrete deck and roof membrane. These roofs are often very garden-like and can generally support significant plantings such as shrubbery.

   More common today are extensive roofs in which only three to seven inches of media are used, often arranged in a modular system. These roofs typically use highly drought-tolerant and hardy, low-growing plants. As such, much less labor is required for their upkeep.

   Green roofs are becoming much more common. While they have a higher initial cost, they are estimated to offer double the lifespan of a traditional roof. This, in combination with the energy savings of the roof, makes them a wise choice for many modern buildings.

The green roof has come a long way from the days of ancient Babylon.

Heather Kuhne is with Doty and Miller Architects, a Bedford firm with a special interest in sustainable design and green building (www.dotyandmiller.com). During the spring and summer, Heather spends her evenings and weekends growing natural heirloom produce for a CSA (community supported agriculture) and farmers' markets (www.basketoflifefarm.com).

Photos courtesy of The Garland Company, Inc. a Cleveland-based manufacturer of high performance roofing materials for commercial, industrial, and educational facilities, established in 1895. More information is available at www.garlandco.com.