Green Roof Technologies

Without question, 2007 gave green roofs and green roof technology an accepted place and a permanent and prominent role in the greening of American cities and architecture. As to actual sales, the year was so significant that one manufacturer of green roofing systems installed more vegetative roofs in one month in 2007 than in all of 2006.

A big turning point in green roof acceptance occurred in 2001 when, with great fanfare, Chicago installed one of the largest green roofs in North America atop its City Hall. Spurred on by the city’s enthusiastic mayor, who was eager to make Chicago the greenest city in the United States, the rooftop garden was designed to test different types of green roof systems and to determine their heating and cooling benefits, success rates of native and nonnative vegetation, and reductions in rainwater runoff.

Monitoring of the roof began in 2002, and the roof still serves as a living laboratory to study green roof technology and its benefits. Results have been encouraging. For instance, studies indicate that the temperature of the existing roof below the green roof has been as much as 78 degrees cooler than the temperature on the traditional black tar roof membrane that still exists on half of the building. This has translated into lower energy costs, especially in the heat of summer, to cool the half of the building with the green roof.

The Chicago City Hall green roof was a turning point for another reason as well. The green roof installed on the building was a conventional built-in-place system, with workers placing soil and planting vegetation directly on top of the building, similar to building a garden. Several challenges were encountered with the installation atop the nearly 100-year-old structure, resulting in the development of a new technology, modular systems, that helped streamline the installation process and make it more cost-effective. With this system, the soil and vegetation are pre-planted in recycled plastic modules off-site, and then the modules are installed directly atop the roof. The system allows for more flexibility and for faster installation, helping to reduce labor costs.

Another advancement in green roof technology that has driven its acceptance addresses the problem of the brutal rooftop environment. In the past 10 years, we have seen the development of engineered soil — soil that is specially prepared with the proper macro- and micronutrients, air spacing, and irrigation capabilities — to help the vegetation on a green roof not only survive but also thrive. Additionally, green roof engineers have been better able to pinpoint specific vegetation native to individual climates — such as sedums, delosperma, sempervivum, and grasses — that can also thrive in these brutal environments.

With positive early environmental and energy results, new technologies in place to help lower installation costs as well as speed up the process, and engineered soil and proper plant selection, it is estimated that nearly 90 percent of the total green roof square footage installed in the United States has occurred from 2004 to 2006. Today, the cities with the most green roofs in North America are Chicago; Washington, DC; and Toronto, Canada.

Another turning point leading to further acceptance of and interest in green roofs has been the result of more and more studies from a variety of independent organizations promoting green roofs’ virtues. For instance:

  • Research from around the world indicates that green roofs reduce annual storm-water runoff from roofs by at least 50 percent, and often by 60 to 70 percent. Moreover, the rate of release following heavy rainfall is slowed, reducing the problems associated with storm surges on local water-treatment facilities.
  • Green roofs have helped reduce the need for air conditioning in many facilities in the summer and therefore reduced CO2 emissions.
  • Green roofs can contribute to biodiversity and address local biodiversity action plans.
  • Green roofs help mitigate urban heat island effect, keeping these areas cooler during the heat of summer.
  • The life of an existing roof is at least doubled with the addition of a green roof, thereby reducing costs for roof replacement and repair.

There are many more reasons why green roofs have finally grown in popularity. What we see happening now and expect to see in the future is even greater acceptance of this technology. With some architects, developers, and campus planners, installing a green roof atop a new facility is already considered mandatory. Green roofs are seen as one way of minimizing a facility’s footprint and impact on the environment as well as a way to give back to the environment.

Jim Lindell is national marketing manager for GreenGrid Green Roofs, a leading manufacturer of Green Roof systems. GreenGrid is a business of Weston Solutions, Inc. Lindell can be reached at [email protected].