This article appeared in The Arizona Republic on June 23, 2004

Planting a roof

Valley could cool if we topped off buildings in soft green instead of red tile

Trim, water and fertilize the roof.

Wacky as it sounds, that could be a strategy to cool off the Valley.

Maintenance is a lot different when the roof is actually alive: a layer of soil planted with groundcover, bushes and even trees.

Using "green roofs" in the Valley could offset some of the extra heat that builds up in the urban area.

Covered outdoor living space awaits, and in the trellised sky gardens.

And, at last, we're getting a real-world project to test out the idea. Optima Biltmore Towers, a Phoenix condominium project at 24th Street and Camelback Road, will use landscaping for roofing. There will be palo breas, pygmy date palms, agaves, vinca and lantana.

Here's hoping it's just the start.

The basic recipe for a green roof is straightforward. Put down a waterproof membrane to prevent leaks. Add a root barrier. Put in drainage and filtering layers. Top with soil from several inches to a few feet deep, depending on the type of plants. The landscaping could be a mix of low-growing plants, such as grasses, or a full-fledged garden setting that includes trees.

Green roofs have so many benefits that the list starts to sound like a late-night TV commercial. If they were cooking gadgets, they'd slice, dice, chop and then do the dishes.

The protection from ultraviolet light makes the underlying roof last much longer, while the extra insulation makes buildings more energy efficient. The plants filter pollutants out of the air.

In wetter climates, one of the biggest advantages is the way green roofs reduce the load on storm sewers by soaking up rain. The natural setting has aesthetic and psychic appeal, a selling point for building owners.

Most important, from our scorching vantage point, is the way green roofs can help offset the "urban heat island" effect. All of the concrete and asphalt in the Valley absorb heat during the day. They're slow to cool down after the sun goes down, radiating heat for hours and keeping the temperatures up. Our nights are getting hotter: The average nighttime low in the summer is almost 12 degrees higher than in 1948.

A green roof absorbs less heat during the day and loses it quickly at night. Plants also act as natural evaporative coolers, when they give off water through their pores.

Green roofing has been popular for years in Germany, where nearly 350 million square feet was installed from 1989 to 1999.

Now Americans are seizing on the idea. In Chicago, about 80 green roofs are already built or under construction. In the renovation of Ford's massive River Rouge assembly plant, about 454,000 square feet of roof will be covered with sedum, a succulent groundcover, and other plants.

Will it work under the searing desert sun?

We don't have the research to tell us. Unlike those in damper areas, where rainwater can be used and stored, green roofs in the Valley would require irrigation. We don't know how that would affect the costs and benefits. Or which plants and designs would do best here.

So cheers to David Hovey, architect and developer of Optima Towers, for simply forging ahead. He already has put green roofs on buildings in Chicago, and he's sure they'll work in the Valley. He's planning a green roof for an upcoming project in Scottsdale, as well.

While Hovey is showing the practical side of green roofs, we still need researchers to evaluate the most effective approach in the desert. It's a project ripe for Arizona State University, which has launched a multidisciplinary study of the urban heat island in the Phoenix metro area.

The Valley's nighttime temperatures are pushing higher and higher. The heat jacks up our air-conditioning bills and strains our energy resources, and makes it miserable to be outside. We're pushing the envelope of livability. If green roofs can help, we should be using them.