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Living Roofs - Concern for the environment spurs interest
by Jenan Jones Benson
Green roofs have been in vogue worldwide for centuries, long before “greening” came on the scene. Some early versions were created out of necessity or lack of alternate materials, while the benefits hit home with others more quickly than with Americans. In the U.S., the initial interest was focused on the aesthetic value of green roofs, which brought elaborate rooftop gardens. Today, energy efficiency and environmental advantages are the perks that are prompting installations of green roofs from coast to coast.
Photo courtesy of Green Roofs for Healthy Cities and Jeffrey L. Bruce & Company. |
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This garden tops an apartment building’s parking structure in Kansas City, Mo. |
Pros and cons
Green roofs clearly win out against traditional ones in the beauty department, but the benefits go much deeper. Green Roofs for Healthy Cities (www.greenroofs.org) identifies selling points in several categories.
From a financial standpoint, long-term cost savings are substantial, despite the fact that upfront expenses outstrip the dollars required for traditional roofs. Green roofs reduce the need for standard insulation and allow smaller heating-ventilation-air conditioning units to be used. Energy efficiency skyrockets. The reduced stormwater runoff may decrease fees associated with its management and/or allow for smaller ponds or cisterns. Roof drains can be decreased or eliminated. Grant funding and other incentives are sometimes available, and marketing potential is maximized.
The earth benefits from improved air quality and the wildlife habitat that the roof may provide. The urban heat island effect is reduced. Using a green roof may satisfy environmental regulatory requirements and green space requirements and earn points towards LEED certification. The energy savings may result in greenhouse gas emissions trading credits. Some are finding that green roofs, and related building practices, facilitate the construction approval process and public acceptance.
For occupants and visitors of a structure, the green roof lends beauty and possibly areas for recreation and food production. Sound insulation is enhanced within the building. In some cases, it brings density bonuses, expanding the floor area ratio.
On the downside, in addition to higher upfront costs, green roofs bring challenges for installers and make future renovations more difficult. Depending upon the design plans, increased structural support and/or plumbing may be required.
Photo courtesy of Green Roofs for Healthy Cities and the Government of the District of Columbia. |
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Reeves Center Green Roof, a city government building in Washington, D.C., was installed by the Office of Property Management in 2007. |
Types of roofs
Nicholas Labadie, senior planner with the Rose Law Group (www.roselawgroup.com ) in Scottsdale, Ariz., has focused on green building in his previous residential construction and landscaping work. He now assists clients with the associated issues that green builders and landscapers face.
Labadie says there are two general types of green roofs. The extensive form is often used when energy savings and maintenance/reduction are the primary goals. These typically are lighter weight with a more shallow growth media, which limits the plant selection. The roof membrane is better protected than traditional exposed membranes, resulting in long life and landscape maintenance needs are minimal.
Intensive roofs are the more complex form, using deeper growth media, diverse plant types, including trees and possibly even water features. They often include usable space for building occupants. Maintenance and installation costs are higher, but the benefits of turning an unused space into an energy-saving feast for the eyes are significant.
Photo courtesy of Green Roofs for Healthy Cities and Rana Creek Living Architecture. |
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The California Academy of Sciences’ 2.5 acres of plant material on its roof makes it the largest of any natural history museum. |
Projects around the country
The Europeans are far ahead of us in green roof technology and policies. Many of the current U.S. practices originated in Europe, and municipal support seems to be more common there. Their experience, along with research within our country, is helping to spread living roofs to more American cities.
The American Society of Landscape Architects installed a green roof on their Washington, D.C., headquarters building in 2006. The demonstration project focused on gathering data to quantify the effects. From July 2006 to May 2007, stormwater runoff was reduced by 27,500 gallons, about three-fourths of the precipitation. With the exception of repeated heavy rains, runoff was eliminated when precipitation was 1 inch or less. The roof successfully reduced the urban heat island effect, lowering the air temperature by as much as 32 degrees during the summer when compared to an adjacent tarred roof. Summer energy expenditures dropped by 2 to 3 percent, while winter bills were up to 10 percent lower. The 2007 book “Green Roof: A Case Study” by Christian Werthmann documents the entire project.
In the warmer, drier Phoenix environment, roofs and their plantings have different requirements and benefits. Optima Camel View Village (www.optimaweb.com/CamelViewVillage), an exclusive LEED certified condo project, offers owners relief from the sun in their living areas by placing green roofs on large overhangs, which do double duty as patios for the units above them.
Green roofs, step by step
One way to evaluate the business potential of green roofs for your firm is to examine the installation process step by step. Labadie says any project should begin with ensuring that the building has been, or can be, modified to offer adequate structural capacity.
A good design will minimize the use of supplemental irrigation; any system that will be used is the first element to be installed. Balance irrigation needs with the limitations of the drainage system. Some systems can distribute inputs, such as fertilizer. Next comes a moisture barrier separating the roof and the planting layer. As with any roof style, minimizing leak potential is crucial. If a top-quality barrier is used, future maintenance needs will be reduced. Common materials include mastic asphalt, PVC and copper sheeting.
Topping the barrier is drainage system and soil stabilizers, which work to ensure that the water is distributed properly when keeping the growth media in place. Labadie says a passive system employing a perforated, interlaced, stiff plastic ribbon is seeing wide use. The ribbon receives the plant material; its gaps between sections form cup-like spaces that are filled with growth media, yielding a stable planting bed. The ribbon’s holes filter water and air, while keeping the soil stationary.
Whatever system is used to house the growth media, its depth determines the viability of the plants and the roof itself. Generally, a 3-inch depth is necessary; the type of media selected may allow a smaller layer.
Plant selection can be trickier than in traditional landscaping. In addition to the usual concerns about climate and water needs, the unique challenges must be considered. A rooftop garden typically has less soil, more wind and little to no shade.
Ongoing maintenance needs vary by project. Other than leak repair, the common tasks of plant care and management of the irrigation and drainage devices translate to rooftop landscaping.
Photo by Kimberly Stockwell-Morrison. |
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Plant selection can be trickier than in traditional landscaping. In addition to the usual concerns about climate and water needs, the unique challenges must be considered. A rooftop garden typically has less soil, more wind and little to no shade. |
Getting started
“For landscape firms looking to get into the field, I would say team up with experienced designers and learn as much as you can before taking on your first project,” Labadie advises. “Being proactive about suggesting the technology, touting the many benefits and finding creative ways to overcome the challenges is the best way to get clients into it.” He adds that the biggest demand comes from large multifamily, commercial and institutional structures.
Manufacturers of green roof systems and related products often supply training. The Green Roofs for Healthy Cities organization has recently initiated an Accredited Green Roof Professional Designation program to help establish an occupational standard in the field. Presented periodically in a number of cities, courses in each aspect of green roofs are offered, including installation. The professional designation is awarded upon successful completion of an accreditation exam. Information is available on the group’s Web site. The first testing session is planned for next spring in conjunction with the annual Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show in Atlanta.
Other organizations, such as the United States Green Builders’ Council (www.usgbc.org) and Sustainable Sites Initiative (www.sustainablesites.org), offer a plethora of information and support. Green Roofs for Healthy Cities has recently published the “Award-Winning Green Roof Design Book,” compiling information on previous winners of its Green Roof Awards of Excellence. The book is available through a link on the group’s Web site.
Although the learning curve may be steep, the new equipment needs are minimal. Other than a system for getting workers, equipment and supplies off the ground, no additional items may be needed.
With consumers eager to save energy costs and protect Mother Earth, green roofs may gain popularity. Coupling that with the challenges of sluggish economic conditions, now may be the time to consider green roof installation as an additional service.
The author is a freelance writer based in Greensboro, N.C.
