What You Can Learn From a Salt Lake City Roof

Just a few weeks ago, I was standing in a garden beautifully landscaped with shrubs, flowers, grasses and a small forest of 20-foot trees. Part of it was formally ornamental and part was planted as a natural prairie of grasses and wildflowers.

A garden has to be pretty spectacular to dazzle me and this was, with its carefully designed feeling of privacy and its wide variety of plants. But my admiration was more than aesthetic.

This gorgeous garden was on a roof -- the roof of the conference center of the Church of Jesus Christ of Latter-day Saints in Salt Lake City. Colleagues at the landscape-design conference I was attending had been telling me I had to see this "green roof," but I was skeptical. Most green roofs are simply a collection of turf or sedum. This one was a complete landscape design on all planes, ground, vertical and overhead.

When I got home and started thinking about it, I realized that what's truly amazing about the whole roof-garden concept is that more people don't have them. The Salt Lake City roof garden is huge. Grasses, trees of all sizes and extensive water features grace the four-acre rooftop. However, a garden can be adapted to fit any roof or terrace that will allow it.

The benefits of gardening on the roof are so extensive that the Environmental Protection Agency is encouraging cities to start roof-garden programs. The EPA's target is the heat-island effect found in cities where nearly every flat surface is paved or built on and nearly every roof is made of dark materials. The result is that temperatures in urban and suburban areas are raised by several degrees.

The EPA estimates that increasing an urban area's acreage of planted space by just a few percentage points can lower temperatures several degrees, significantly reducing smog and saving millions of dollars in energy costs. It may also save lives, as excessive heat can be deadly, especially to people who are already frail because of youth, age or illness.

Roof gardens have great advantages for anyone with a suitable structure. They reduce heat loss in winter and heat gain in summer, cut water runoff by as much as 50 percent and put to good use an otherwise unused space, providing habitat for birds and butterflies. Using the rooftop expands living space for activities such as dining or recreation, takes advantage of city views and might increase property value.

Besides the practical value, roof gardens can be as varied and as stunning as in-ground gardens. In their 1999 book "Gardens in the City: New York in Bloom," author Mary Jane Pool and photographer Betsy Pinover Schiff capture some spectacular roof and terrace gardens. They found a Japanese garden with bamboo plants and screening; a turfed play yard with a swing set, slide and sandbox; and a penthouse terrace with trellised vines, a fountain, half a dozen types of trees and a screened lattice gazebo. In several cases, the plants not only provide beauty but also screen mechanical systems or ugly views.

Obviously, not everyone with a roof can have a roof garden. Not all roofs are flat enough or can stand the extra weight. They can't all be easily reached. If your roof or terrace belongs to a landlord or a condo-owners association, use may be restricted or forbidden. (In such a situation, check with the owner to see whether you would be allowed to build.)

But if you have the right slope, a sturdy enough structure, a good way to get up there and a little imagination, you can have the crowning glory of a roof garden.

You need to figure out whether the roof and the structure are strong enough to support extra weight. Get an opinion from a structural engineer or architect. You can also ask what, if anything, you should do to the roof or to the flashing to make sure you're not going to encourage leaks.

There are many ways to protect a roof -- there's membrane sheeting just for that purpose. If you're going to be using turf, you may need a system of under layers, including plastic foam or gravel, as a foundation. You might need to consult a landscape professional with some experience in green roofs.