Surely it sounds peculiar, but one of the hottest trends in landscaping is taking place in urban centers. Cities are looking to control stormwater runoff, increase air quality and reduce the urban heat island effect. Companies and property managers are looking to save on energy costs, increase the value of their property and provide green space for workers and residents.
Through green roofs, landscapers can capitalize on those needs in big ways.
“There is no other type of building technology that provides the same scale and scope of benefits as does a green roof system,” says Steven Peck, founder and president of the organization Green Roofs for Healthy Cities (GRHC).
A growing number of consumers are buying into that theory. The North American green roof industry grew 28.5 percent in 2010, after seeing 16 percent growth in 2009, according to GRHC’s annual survey. More than 700 projects that represented 4.3 million square feet of installed green roof space were listed in 2010.
And the growth isn’t expected to stop anytime soon.
“I think the industry is poised for some significant growth without a doubt, because we have a tremendous need to use roof space, to have our roof space help clean the air, and manage stormwater, and provide green space and grow food in our cities,” Peck says. “These roofs can do a lot for us and there is just a ton of roof space available. But it has to be done by professionals.”
Designing landscapes for a roof. The idea of working with a blank slate might sound intriguing. But remember, everything changes 10 stories in the air.
There are two factors that need to be considered before the design process begins. “No. 1, we have to know what the structural load capacity is for the rooftop. That is going to tell us how much additional weight we can put on that roof, if any,” says George Irwin, president of manufacturer Green Living Technologies International, which is headquartered in Rochester, N.Y. A structural engineer will need to be consulted and should provide a signed letter with the precise weight limit allowed.
“No. 2, there’s no reason to go into a lengthy, costly design process with the client until we know what we’re designing for,” says Irwin, who taught a green roof course at the GIE+EXPO in 2010.
Green roofs are popular because they provide extra amenity space and an aesthetic to buildings. They also offer economic savings, as well as environmental benefits.
Economically speaking, green roofs protect the roof membrane, which results in an estimated lifespan of two times longer, and depending on the type of green roof they can significantly reduce heating and cooling costs. GRHC cites a field experiment in Canada that found a 6-inch-deep extensive green roof reduced heat gains by 95 percent and heat losses by 26 percent.
Environmentally speaking, buildings are the worst emitters of carbon dioxide, says Irwin, who started as a landscaper and grew his green roof company into a one-stop shop as a designer, installer, maintainer and manufacturer. Green roofs can reduce the amount of carbon dioxide and can be used as a retainer for stormwater runoff.
One of the first conversations with the client should entail what they hope to get out of the space.
Depending on how the client wants to use the space, how they want it to perform and how much weight the roof can hold, the green roof can take on different forms. There are two main types of green roofs – intensive and extensive – the difference being the soil profile, plants and how the systems are installed. In 2010, 3.1 million square feet of extensive green roof space was installed compared to 172,000 square feet of intensive and 312,000 of semi-intensive/mixed, according to the GRHC’s annual survey.
“Anywhere from 3-6 inches (of soil) is a typical extensive system,” says Alex Fransen, landscape development manager of Steele Blades Lawn & Landscaping Services in Louisville, Ky. “Then anything from about 6 inches up is going to be an intensive system. Typically on your intensive systems you’re going to see your normal landscaping plants like shrubs and trees.”
As the vision for the green roof takes shape, it’s important to understand the codes and regulations that need to be included in the design. “There are a lot of rules and regulations and there are more coming out every day it seems like,” Fransen says. “There is a lot of fire safety stuff now that you have to be aware of – a lot of roofs they want irrigation systems on per code for fire suppression also.”
Steele Blades entered the green roof market about three and a half years ago, and Fransen’s experience has taught him to constantly look for regulation updates on GRHC’s website and for information on local and national codes. The big concern last year, he says, was cutting back on plant material that could easily dry or die and would be susceptible to burning, whether because of cigarette ash or solar activity.
Picking the right plant material is essential for the green roof’s success and it’s one of the biggest mistakes designers make.
The plants growing on the roof will face wind, temperature and growing conditions unseen on the ground.
Recommended vegetation will vary based on location, but native, drought tolerant, hardy plants that can withstand thin soil work best.
“The traditional European sedum varieties – that’s where green roofs started – there’s no reason to abandon them, they’re made for green roofs,” says Roger Grothe, president of Aloha Landscaping, headquartered near Minneapolis. “They’re drought tolerant, very hardy, colorful, and there’s probably 40 varieties.”
Grothe, who has been working with green roofs for eight years and is getting his Ph.D. in environmental science and green roofs at the Finnish University of Helsinki, is researching green roof plant varieties. “Each area, whether it’s Guam, whether it’s Minnesota, Georgia, there’s just a little trial and error and each roof is a little different.”
As the design process takes place, that’s the best time to create a maintenance plan.
A perk for landscapers installing green roofs is the additional revenue of then maintaining the system. “The best practice for maintenance is to have a five-year maintenance plan, not a one-year-maintenance plan or a two-year,” Peck says.
Installing A green roof. The most important aspect of a green roof isn’t installed by a landscaper – at least, it shouldn’t be. A reliable waterproofing membrane will make or break a green roof. And most say laying that layer is a job better left to those who specialize in that area, roof or waterproofing contractors.
“Unless you have someone who has several years in that industry and knows what they’re doing, I would suggest not trying to do that,” Fransen says. “It’s another beast, and it’s nothing we want to get involved with, we have our hands full as it is.”
Once the roof is properly waterproofed and tested for leaks, the remaining components of the green roof can be installed. Still, it’s not as easy as creating a landscape on the ground.
When it comes to putting people and products on the roof, safety is a huge issue – not only for the people on the roof but those on the ground. “Working on the roof is much different because No. 1, you’re elevated and there are elements on the roof top that don’t particularly apply to ground-level landscaping,” Irwin says. “One is wind and environmental conditions. It’s much different when you’re four stories in the air because even a single piece of plastic that flies off the roof can be detrimental.”
Also, if an error is made during the installation process, it could puncture the waterproofing membrane, essentially killing the project before it’s completed.
Proper training and planning goes a long way. The project should outline variables such as the materials that are going to be installed on the roof and their weight, how they’re going to get on the roof, who is going to be involved in the process and what specifically will each person be doing.
“Most roofs now are under very close scrutiny by OSHA because there have been so many problems,” Grothe says. “A lot of roofs you have to have what they call a pick plan, where you specifically outline all of the weights and all of the angles and the certification of whoever is operating that crane. It’s not something you can just call up and say, ‘Yeah, put this up on the roof and haul up this soil.’ You really need to understand how all of that is changing.”
The green roof is going to involve a drainage system, a filter layer, an irrigation system and some form of growing media along with the vegetation – and all of it is built, not dug. This is where understanding the products on the market and how green roofs work comes into play.
Green roofs aren’t a rubber stamp situation, Grothe says. Different products might be better and easier to install on different roofs. “You have to evaluate each situation, understand what’s going on, and then try to design a system that is going to work,” he says.
Green roofs can be built traditionally by bringing in each component and building a system. Or there is also a modular or tray system, which can best be described as putting together a puzzle. The layers of the green roof are compacted into the modular system and then placed side by side on the roof. An ideal situation for a modular system would be installing a green roof on a 20-story building that has elevators, but no access for cranes.
Grothe estimates 70 percent of the green roofs installed in the U.S. are traditional and 30 percent are trays.
“Understand what the different systems are and how they go on,” Peck says. “The green roof industry is complicated, there is a lot of complexity there and it’s really important that people take the time and make an investment – it’s a relatively modest investment – in getting the proper training, otherwise they can cost themselves a lot of hardship and potentially damage the industry.”
The author is an associate editor at Lawn & Landscape. She can be reached at firstname.lastname@example.org.
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