Green Roofs - The future is already here!

by Leslie Gillet

America’s rooftops could generate 964 TWh (24 percent of US sustainable electricity needs) if solar shingles were used to roof an average of 540 square feet of every dwelling. Many open air car parks could also be covered, providing welcome shade for the vehicles.

-Guy Dauncey,

Green roofs are a concept familiar to most people now as they’ve become very popular in recent years. Green roofs are an extension of the existing roof that allows plants, trees, and shrubs to grow in a lightweight growing medium. Generally green roofs are on top of a human-made structure and can be located below, at or above grade.

There are three types of green roof systems:

  • Complete systems where all different components including roof membrane are an integral part of the whole system
  • Modular systems that are positioned above the existing roofing system
  • Pre-cultivated vegetation blankets that consist of growing medium and plants that are rolled onto the existing roofing system with drainage mats and root barriers as required.

As with any environmental feature, there are costs associated with the installation and maintenance in order to enjoy the benefits of the green roof. As new products are perfected, associated costs and efficiency of installation and use will make going green easier and less expensive.

Toyota Roof Gardens, a subsidiary of the car company, has developed the TM9 self-watering turf mat, a system composed of 20 inch squares of grass on an irrigating base. The system is designed for building green roofs as easily as laying down carpet, and since the base layer connects directly to irrigation systems, the mats are self watering.

The unit is only 2 inches thick, which results in a reduced roof load compared to other types of green roof systems that contain a thicker soil layer. The grass itself is a special brand of Korean velvet grass that only needs to be cut once a year. The system has a price of US $43 per 20 inch square tile, which is still a bargain in terms of reduced installation and maintenance costs, as well as a cost savings if the building’s roof doesn’t need any structural upgrading to account for the increased weight of a conventional green roof.

This system, as with all green roofs, provides a natural cooling effect as well as excellent thermal insulation for a building. Green roofs can also remove carbon dioxide from the air and supply oxygen, and are an excellent addition to any flat-roofed building. The TM9 turf mat would be an easy way to add a green roof to almost any building. It might even be possible to install the system inside, to make living carpet.

Green roofs aren’t the future: They’re already here. In Chicago, 2.5 million square feet of downtown roof space is now covered with hardy plants such as sedum and prairie grass – the better to lower heating and air-conditioning costs (by 10 percent or more) and dramatically reduce rainwater runoff.

The Windy City’s rooftops aren’t alone: The total square footage of green roofs in the United States is growing at the healthy rate of 125 percent a year.

Solar Shingles

Solar shingles are another interesting roofing innovation. Why not put the sunlight your roof soaks up during the day to good use?

Photovoltaic (PV) shingles provide the same look, protection, and durability as asphalt shingles but have the added benefit of converting sunlight into electricity that can power your home (or specific appliances), reducing the need for electricity generated from fossil fuels and lowering your electricity costs.

PV shingles work best on south-facing roofs that are not shaded by trees for a significant portion of the day. To determine the best solar energy option for your home or find a professional installer, visit the Canadian Solar Industries Association, a joint industry-government information resource at

Green Walls

While you are renovating or starting a new building project, here’s another idea: green walls.

“They’re taking off faster than green roofs,” says Chad Sichello, president and CEO of G-Sky, a Vancouver, British Columbia, company that offers both.

Starting at $100 per square foot, G-Sky will install plant-filled wall panels that can go on any vertical surface – meaning G-Sky just quintupled its opportunity. After all, “for every roof out there, there are four walls,” says Steven Peck, founder of the Toronto-based industry association Green Roofs for Healthy Cities, who says he expects the vertical greenery market to be “huge.”

Green walls can provide as much money-saving insulation as green roofs, but put less load-bearing strain on the building. Whole Foods, Vancouver International Airport, and the W Hotels chain are early G-Sky clients.

Carbon Trading

And that’s just the start. G-Sky is looking long-term, to a world where carbon-trading is king and companies are eager to offset their greenhouse gas emissions. What better way to do that than to cover your building with greenery?

“Even in small plants, there’s a very easy calculation for how much carbon they offset,” Sichello says.

Green walls can also help offset the newly identified urban heat island effect: All the heat-absorbing surfaces in a city raise its temperature to as much as 8 degrees higher than that of the surrounding countryside. Peck says no North American city will have enough green roofs and walls to combat this effect before 2027 – not even Chicago.


Sources and links:;

[Watershed Sentinel, May-June, 2007]

Watershed Sentinel Original Content

5 Issues/yr — $25 print; $15 digital