Rooftop gardens are becoming more and more popular in big cities where space for ground-level gardens is not available.
The basic elements for a green roof are hard-to-kill plants, (as it is usually hot and dry and windy), and a layer of soil. However, it is becoming popular to add insulation and systems that absorb storm-water run-off and deflect some of the solar heat.
The creation of a viable garden hundreds of feet above ground demands experts who understand engineering, water proofing, irrigation systems and soil principles.
Frequently a crane is also an essential part of the installation. Additionally, a building's structure must be strong enough to support the considerable weight of a roof garden.
Despite the expense, residential demand for roof gardens has grown about 15% to 20% each year over the past decade, according to Ed Jarger who works for American Hydrotech. He says that the cost of installing his company's watertight rubberized asphalt membrane, overlaid with a root barrier, as well as insulation, a drainage and water retention layer and a carefully mixed growing medium, is between $30-60 per square foot or more. But for many who can afford it in places like New York City, the green space is well worth the price!
For more information, read Amy Gamerman's article "Raising the Rooftop Garden," (Wall Street Journal, June 13, 2014).