Jefferson Community and Technical College in Louisville, KY recently hosted a symposium on green roofs and walls. Not only was the information interesting and exciting, but the speakers and presenters were passionate and engaging. These people really seem to know their stuff! After a full day of hearing from subject matter experts, for me the bottom line seemed to be that a green roof or wall system is best utilized when it is integrated with the rest of the building’s systems, and when the design considers each project’s unique location and environment. In other words, a green roof in Arizona should be different than a green roof in Kentucky.
So what is a green roof or wall? The more often utilized of the two is the green roof, which is basically a garden or planting system, with soil and organic matter, installed on a roof. A green wall basically flips the garden roof vertically. The benefits of these systems are numerous. Green roofs regulate the interior temperature of the building, therefore decreasing HVAC use and energy bills. With the addition of plants essentially creating a garden space, the rooftop becomes an additional level to the building, which can be used for company meetings, as a break area, social gathering place, or as one presenter displayed, a playground and garden for an urban school in Cincinnati. Additionally, green roofs help mitigate what is known as the “heat island effect” by creating a water-permeable, non-reflective surface (see here for more information about urban heat islands). A green roof’s permeable surface also helps mitigate and control stormwater, and acts as a bio-filter. According to many experts at the symposium, green roofs extend the life of the roof to 40 or more years. Additionally, green roofs create a natural sound insulation, and create a habitat for indigenous wildlife. Green walls provide landscaping opportunities in urban or densely populated areas with limited horizontal land surface. Additionally, green walls purify the air and also provide sound insulation.
So, how are the functions of a green roof desirable? Currently, the trending “drivers” of green roofs are the positive effects of the integrated design, in other words, the reduced utility bills and the additional floor space provided. There are other benefits as well. In the Ohio River Valley, heat and pollution contribute to the population’s increased asthma and allergy symptoms. Louisville Mayor Greg Fischer has launched a program to track 600 asthma inhalers equipped with GPS in order to pinpoint areas in the city where people are experiencing increased asthma attacks. This information can then be cross-referenced with areas of high heat to determine if there is a correlation, and to provide support. In a place like Louisville, where the sewer and stormwater systems are often filled to capacity, slowing the flow of water with a green roof system which also filters the water is very beneficial to the entire city.
Most green roofs are located on the top of commercial buildings, which typically provide a more level surface as opposed to the angled roofs on typical residential homes. However, industry experts at the symposium made it clear that even steeply angled roofs can be made to accommodate a green system; one speaker announced that his company had installed a green roof on an 80 degree surface (which is, arguably, more like a green wall), indicating that it is simply a matter of design and engineering. Though green roofs strive to be relatively low maintenance by utilizing hardy, indigenous plants, a steeper surface also creates some challenges when it comes to upkeep.
Which leads to another important aspect to green roofs – the longterm cost of maintenance and upkeep. Again, these systems are meant to be largely self-sustaining, so plant species selection is important. However, even low-maintenance plants require some care. If your area experiences a harsh winter, some plants may die off and will need to be replaced. Developers (or home owners) looking to install a green roof should weigh the pros and cons, and consider the long-term payoffs and short-term costs.
The cost of a green roof varies, depending on the size and the level of care needed. For instance, a rooftop garden will probably cost more than a rooftop field of grass. Universities can help connect developers to research funds. Many presenters at the symposium encouraged developers to integrate research into their green roof design, thus enabling each green roof to contribute to a growing body of knowledge. Local governments may also provide incentives for green roofs, and local utility companies may help fund the effort as well.
The success of a green roof or wall is contingent upon its integration into the entire building’s systems, and the systems (both man-made and natural) of the surrounding environment. Developers should think of each building and its components as pieces of a whole system. Green building efforts are best approached with regional and local considerations – not all plants are successful in all regions, and not all regions experience the same weather and stormwater patterns. It wasn’t that long ago that green roofs and walls were considered radical and somewhat “on the fringe,” but as the reputation and knowledge improves, more and more developers are seeing the benefits.
Have you ever seen or experienced a green roof? What was your impression?
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