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Green Wall Effect on Heat Island vs. Other Structures
Green Wall Effect on Heat Island vs. Other Structures

People who work with concrete, especially those who have worked with it for many years, know the product's upstanding environmental properties. When Mark Woolbright visited Europe, he noticed that many locations had concrete retaining wall block that was plantable.

“European city planners have been dealing with high population density forever, so they've realized that even their walls need to maximize green space and stability,” says Woolbright.

Woolbright, who invented the Hercules retaining wall block and founded St. Louis Retaining Wall Co. 17 years ago, recognized the wisdom of this approach. “I've always been a green space guy,” he says, “But in the U.S., there hasn't been much interest in plantable walls.”

Instead, his company marketed the structural benefits and quality of its block. Some customers chose Hercules because it was plantable, but for most it was a secondary benefit. Woolbright dreamed of the day when he could make a green sale. In his mind, that was what truly set his block apart from the competition.

“Since the sustainability movement really got going, there has been a sea change. ‘Green' has become the buzzword,” he says. Now St. Louis Retaining Wall Co. has a new crop of customers looking for sustainable solutions, and green walls have taken on a new meaning.

Over the years that St. Louis Retaining Wall's customers were building plantable walls, the company studied and tracked their results. They knew the walls were attractive, absorbed less heat than bare walls, and helped reduce surface water runoff, but there was no formal research to prove it. That all 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, but with even more potential,” he says. While building owners may not have the extra money to create a green roof, they can choose to grade their property with a green retaining wall at about the same cost as a non-planted wall. Also, there are usually more sustainable landscaping opportunities on a property than the green space that's confined to the top of a building.

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LEED credits

Often, a green wall can actually contribute to more Leadership in Energy and Environmental Design (LEED) credits than a green roof, including Innovation in Design, Site Development, Stormwater Design, and Heat Island reduction.

When he learned that SIUE's research into the most effective plants on green roofs focused largely on the same ones that thrived in green walls, Woolbright was convinced he needed to start a new research project. Dr. Bill Retzlaff of the Environmental Sciences Program, and Dr. Susan Morgan, Department of Civil Engineering, also saw the benefit of creating a green wall research project for SIUE graduate students.

The project, launched in September, focuses on 18 test walls built with EcoWorks block. AmerenUE, a power company, donated bottom ash, a byproduct from its coal-burning facility, and Charah Inc., a bottom ash processor, pre-screened and bagged the material. Jost Greenhouses provided the plants.

St. Louis Retaining Wall employees helped SIUE students and staff install the test walls, which students will monitor for plant growth, thermal benefits, and stormwater control over the next three years. At the end of the study, Woolbright expects the facts will support his green wall crusade. Once the research is published, there may be a lot more demand for his green ideas.

St. Louis Retaining Wall's block has a shallow, tray-like design with a flat front. Units come in interchangeable sizes and shapes that can create variable wall setbacks, allowing from 40- to 70-degree inclines.

The block also allows for thin structural cross sections, giving designers many site layout options. The one-block system does not use corner or cap blocks. Its utilitarian design makes sense, considering this block is meant to be covered up as soon as it is installed.

Woolbright also has developed EcoWorks, the company's smaller retail block. The unit is sold in a kit with bags of blended media for infill and plant options. The infill media makes EcoWorks greener than the average planter block. It is a proprietary blend of post-consumer waste, compost, and fertilizer, blended and pH-balanced to nurture plants that work best in retaining walls.

Visit or e-mail Mark Woolbright at for more information.