By Bill Ward
Published in The Boerne Star in December 2006
While Kathy and I were visiting in Austin last week, our friend Les White thought we would like to take a tour of Escarpment Village, a shopping center near his house. Now, I definitely am not into shopping centers, but Les was correct. This one we did want to see.
All the landscaping in Escarpment Village is done with native plants and “native-compatible” plants, reportedly under the guidance of consultants from the nearby Lady Bird Johnson Wildflower Center. All the grasses, flowers, shrubs, and trees planted there can tolerate the hot Austin summers with a minimum of irrigation.
The nicest surprise in the shopping center was a view of the roof from Starbuck’s. As we sipped our mocha at an upstairs table, we looked out on a native prairie! It was a nice sight. A gentle breeze sent ripples through the Mexican feathergrass, little bluestem, and a few other grasses I could not identify from the window.
There also are non-prairie plants, such as the agarita bushes taking hold in a few spots. Although we couldn’t identify several other forbs in their winter condition, we recognized Virginia creeper and crossvine clinging to the low walls around the rooftop prairie.
We were looking out on Austin’s first “green roof” on a commercial building. This roof prairie occupies several thousand square feet (reports range from 7,000 to 9,700 square feet) and replaces the usual asphalt and gravel or shingles. Heather Venhaus, an environmental designer at the Wildflower Center, directed the planting.
The plants on this roof grow in shallow two-by-four-foot plastic trays filled a few inches deep with special “soil” mix. Under the trays is a porous medium that aids drainage, and under this a waterproof membrane. Roofs of this sort are called “extensive” green roofs, as opposed to “intensive” green roofs, which cover a small area and contain deeper soil.
Extensive green roofs are a challenge, especially during Texas summers, because the plants must subsist in only a few inches of the growing medium. The Wildflower Center is conducting green-roof experiments to see which native plants will grow well in the rooftop habitat. On the Wildflower Center grounds, they constructed five-by-six-foot test roofs, on which they planted a variety of drought-tolerant wildflowers, grasses, sedges, and vines.
The extensive green roof at Escarpment Village is the first in Texas to use exclusively native plants. It has become part of the Wildflower Center experiments. The research on green-roof technology at the Wildflower Center is sponsored by the City of Austin and by the roofing industry.
One advantage claimed for green roofs is that they retain, and thereby reduce, storm water. Any excess storm water from the Escarpment Village green roof is directed into two large water-catchment tanks near the entrance to Starbuck’s. According to a Starbuck’s employee, all the water used to irrigate the roof plants comes from those tanks.
Other advantages attributed to green roofs are 1) reduction of the heat-island effect in urbanized areas, 2) filtration of pollutants from storm water, 3) increasing energy efficiency of the building under the green roof, and 4) lengthening of roof life span because of the protection from hail, extreme temperatures, and direct sunlight.
Another advantage that would play well in the Hill Country is that the green roofs are way out of reach of browsing deer.
