To people who work with concrete, its environmental properties are nothing new. When Mark Woolbright, founder of St. Louis Retaining Wall Co. 17-years ago, visited Europe, he noticed most of the concrete retaining walls were plantable.
Woolbright, who invented the Hercules retaining wall block, saw the wisdom in this approach. “Unfortunately, in the U.S. there hasn't been much interest in plantable walls,” he said. Consequently, his company marketed the structural benefits and quality of its block.
“Since the sustainability movement really got going,” he stated, “there has been a noticeable change.” Now, St. Louis Retaining Wall customers are looking for sustainable solutions, and “green” walls have taken on a new meaning.
St. Louis' block has a shallow, tray-like design with a flat front. Its interchangeable sizes and shapes can create variable wall setbacks, between 40 deg and 70 deg of inclination. The block also allows for thin structural cross sections, providing many site layout options. The one-block system does not use corner or cap blocks. Its utilitarian design makes sense, considering this block is usually covered up soon after it is installed.
EcoWorks, the company's smaller block, is sold in a retail kit with bags of blended media for infill. The infill media makes the block greener than the average planter version.
Green wall research
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The company studied the results of customers that built plantable walls during those early years. They knew the walls were attractive, absorbed less heat than bare surfaces, and helped reduce water runoff, but had no formal research to prove it. That changed when Woolbright attended a green roof symposium at Southern Illinois University Edwardsville (SIUE).
“I realized that green walls have a lot of the same sustainable characteristics as green roofs,” he recalled, “but with even more potential.” While building owners may not have extra money for a green roof, they can grade their property with a green retaining wall at roughly the same cost as a non-planted wall. A green wall also qualifies for many Leadership in Energy and Environmental Design (LEED) credits, including Innovation in Design, Site Development, Stormwater Design, and Heat Island.
Woolbright was convinced they needed a new research program when he learned that SIUE's studies of the most effective plants for green roofs focused largely on the same ones that thrived in green walls. Dr. Bill Retzlaff of the Environmental Sciences Program and Dr. Susan Morgan in the Department of Civil Engineering agreed and established a green wall research project for graduate students.
The project, launched shortly after Labor Day 2007, focused on 18 test walls built with EcoWorks block. St. Louis Retaining Wall employees helped SIUE personnel and staff install the test walls, which students will monitor for plant growth, thermal benefit, and stormwater control over the next three years.
Green Wall Effect on Heat Island vs. Other Structures