The Gordon Persons Building’s roof is classified as an extensive green roof, meaning it supports 10 to 25 pounds of vegetation per square foot and was designed to be virtually self-sustaining.
Greenery and gardens aren’t just found on the ground. Green roofs, which partially or completely cover a building with vegetation planted over a waterproofing membrane, exist all over the world, from the tops of small houses on remote islands to congested city skyscrapers. These roofs offer many benefits, especially for urban buildings such as the Gordon Persons Building in Montgomery, Ala.
As part of a renovation in early 2014, a green roof was installed on the Gordon Persons Building, which houses Alabama’s Department of Revenue. The underlying structure of most green roofs is often built with steel parts. But contractor J.J. Morley Enterprises Inc. opted to use composite beams and grating from Strongwell to complete the project.
Green roofs help to mitigate warm temperatures in cities because they absorb carbon dioxide and decrease the amount of dark rooftop space that would absorb heat. The roofs also reduce heating and cooling loads on a building by 50 to 90 percent by adding mass and thermal resistance and through evaporative cooling, respectively. In addition, green roofs absorb rainwater, reducing stormwater runoff by up to 75 percent.
The Gordon Persons Building’s roof features 26 separate planters, each in varying geometric shapes spread across six rooftop courtyards. A mix of perennial plants suited to Alabama’s climate were pre-grown in vegetation trays with a drainage layer made from 100 percent recycled high-density polyethylene and bio-degradable walls made of recycled paper products with 20 percent wax content. The vegetation trays were then placed on FRP beams and grating, which were inserted inside reinforced concrete planters on the courtyard floor.