Defining the Green Roof

by Renee Rutledge
(Bay Area, California)

There are many ways to be "green"; apparently, on the roof as well. When someone mentions a green roof, a range of different images can go through your mind. Most applications of the green roof entail environmental friendliness, but this isn't always the case. Here's a selection of different roofs, all considered "green," but for different reasons.

Roof Gardens

Designed to be viewed and enjoyed, roof gardens can include lawns, flower beds, shrubs, trees, and other plants that make a roof look and feel alive. Roof gardens commonly sit atop the indoor shopping mall or office building. They look pretty and exist for recreation, complete with foot paths for limited access to someone in need of a well-deserved break. But are these roof gardens green for other than aesthetic reasons?

As a matter of fact, they can be. Roof gardens can be extensive and designed to limit or prevent access by pedestrians. These roofs are meant to improve building insulation. Also, because the plants usually consist of hardy, water absorbing sedums, the roofs help manage run-off after heavy rains. They even provide a wild and self-sustaining habitat for displaced local wildlife that find shelter there. These extensive roof gardens are pretty much synonymous with the eco-roof, or living roof, described below.

Eco-Roof/Living Roofs

Popular in Europe, living roofs are now catching on in the U.S. They are typically covered with 4 to 6 inches of soil and vegetation. The soil filters pollutants out of rainwater while the greenery filters pollutants out of the air. Because cities are filled with hard surfaces that heat up in the sun, the air in cities is warmer, creating higher pollution levels and increased cooling and energy costs. Living roofs reduce this "heat island" effect, provide extra insulation for the building, and protect the roofing material itself from weather damage. The native plants located on living roofs help sustain local wildlife. Not only that, but living roofs are recognized for their aesthetic appeal, too. If you are considering a roof garden or living roof, evaluate how much weight your roof can hold, the necessary materials, including soil and plant types, and construction procedure, including the need for a waterproof membrane.

Conventional Materials with Green Properties

If the roofing material you select is energy efficient, it can go a long way in keeping your heating and cooling costs down. Cool roofs such as metal and clay varieties are recommended in hotter climates because they can deflect up to 50% of the sun's solar energy. In addition, metal and clay have higher insulative value than others.

The way your roofing material is made and disposed of will help pinpoint how green it is. Most options are available recycled, such as metal, slate, clay, and now, even rubber and plastic. These products help deflect the large amounts of roofing materials contributing to solid waste generation in the U.S.

When considering your roofing type's life cycle, you want something that is durable and long-lasting to help offset the money and resources that will be needed to replace it. Asphalt, for instance, is not green because it normally can't be recycled, is made from petroleum products, and can release chemical pollutants when it's applied. Wood will crack and decay over time. Metal and slate roofs cost more but can last twice as long. On the other hand, some varieties of metal are prone to rusting, and slate takes a lot of energy to produce if you don't purchase it recycled.

There are obviously lots of angles to look at, and choosing one thing may mean sacrificing another. The key is to look out for energy efficiency, durability, and a sustainable life cycle. Finding balance can only be done on an individual basis, depending on your location, energy use, budget, and priorities. The good news is that the choices to go green on the roof- are definitely out there.

Renee Rutledge is the editor of CalFinder's Green Remodeling Blog
, where she writes on topics of sustainability in remodeling ideas and home improvement.

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