The dirt on green roofs
By Michelle Warren • Bankrate.com

Forget curb appeal. Progressive homeowners are interested in green appeal and they're starting at the top, opting for green roofs designed to save energy and the environment.

While the first thing that springs to mind is a roof-top garden, green roofs are so much more and less. In essence, they're an extension of an existing roof, however they include waterproof and root-repellent materials, as well as drainage, filters and growing matter, all designed to sustain vegetation. While intensive green roofs have a garden-like feel and can host several different kinds of plants, extensive roofs are often inaccessible with simple, hardy greenery.

Alex Johnston, administration coordinator for Green Roofs for Healthy Cities, a Toronto-based non-profit association, says "the modern version of it grew up in Europe," but green roofs are gaining momentum in North America; reports show 72 percent growth in green roof square footage between 2004 and 2005. While the early adopters are large industrial companies, there's also a residential movement.

"It's something that people are definitely interested in," says Johnston. The group's comprehensive web site is an invaluable source for information and companies that offer green services.

Laura Barker, sales manager for Elevated Landscape Technologies of Brantford, Ont., says it's possible to green virtually any size and slope of roof. New technologies, along with record hot summers, rising energy costs, environmental concerns and a desire to differentiate one's home, are all giving rise to the green roof movement. "It's growing all the time," says Barker, adding that not only are there practical benefits, but "it's very decorative." She's seen green roofs applied to everything from garden sheds and gazebos to dog houses.

Green benefits
Earlier this year, Toronto City Council became the first in North American to adopt a comprehensive set of green roof policies. The move came after a city-commissioned study by Ryerson University that found if eight percent of the rooftops in the city were covered with extensive green roofs, it would generate more than $300 million in initial cost savings in the areas of storm water management, combined sewer overflow reduction, building energy expenses and urban heat island reductions. In addition, the city would save approximately $40 million a year on operational costs.  

Numerous studies outline the benefits of green roofs for:

• Collecting storm water that would otherwise go into the sewer system, affecting drinking and swimming water, as well as polluting lakes and streams. • Reducing the "urban heat island" effect by lowering a city's temperature (studies show widespread green roofs in Toronto would reduce the city's local ambient temperature between 0.5 and two degrees Celsius). • Acting as insulators, reducing cooling costs in the summer and heating costs in the winter (a study out of Germany shows green roofs can help a building retain up to 50 percent of the heat typically lost to convection). • Creating opportunity for food production in urban areas. • Beautifying cities. • Improving air quality by filtering air particles and reducing green house gases. • Providing sound insulation by absorbing, reflecting or deflecting noise from heavy machinery, planes or traffic.

For the average homeowner grappling with rising energy costs, the insulation factor alone holds appeal. A typical one-story building with a grassy roof and about 10 cm of growing medium, for example, would result in a 25 percent reduction in summer cooling needs, according to Environment Canada. "Many people no longer use air conditioning after they install a green roof," says Barker.

To green or not to green
Despite increased interest, there are many misconceptions about green roofs.

"A lot of people think they require a lot of maintenance, which they don't," says Barker. Most extensive systems need little more than occasional watering, which can be accomplished with a soaker hose. From there, the level of care depends on the complexity of plant species.

Also, roofs don't have to be flat. The ELT Easy Green system, for example, adheres to roofs sloping as much as 30 degrees, while the Easy Green Living Wall system works on steep slopes and even vertical walls.

As for the danger of your roof caving in under the weight, Barker points out green roofs weigh only about eight pounds per square foot when saturated. Load capacity isn't a problem in newer homes, but in older Victorians, for example, it can be an issue.

In addition, green roofs have a high-quality membrane to protect against leaks, and it's been proven that the roofs last about twice as long as regular roofs because the vegetation offers protection from harmful UV rays, as well as seasonal heating and cooling, which causes a normal roof to expand and contract. As a result, while green roofs are more expensive than shingles (about double the price), maintenance and replacement costs are lower.

How much will it cost?
There are a number of variables that influence green roof prices, including size of area, depth of growing medium, plants selected, irrigation and whether a roof is to be accessible or inaccessible.

Keep in mind that intensive systems tend to be the most expensive as they offer vast possibilities when it comes to plant life and design (they also offer greater benefits when it comes to insulation and energy savings). Extensive systems are less expensive as they're a simple covering of hardy sedum designed for the best drought tolerance and lowest maintenance. The ELT Easy Green system, for example, ranges from $12 to $20 a square foot, with $12 being about average.

Barker points out users "get (the investment) back in energy efficiency." 

There are generally three types of green roofs. A complete system means that all components, including the roof materials, are an integral part of the system, while a modular system is positioned above the existing roof; it essentially consists of trays or containers or plants spread on the roof. Another alternative is pre-cultivated vegetation blankets.

When getting a quote, make sure it includes not only the system, but delivery, installation, design and maintenance.

Getting started
Arm yourself with your roof's size, slope, load-bearing capacity, drainage systems and other features, such as skylights. Also take note of climate (you'll want vegetation that's native to the area and can withstand all types of weather), sun and wind exposure.

Some companies offer do-it-yourself kits for residential roofs, but when it comes to going green, it pays to first do your homework and seek expert advice.

Michelle Warren is a writer in Toronto.