Sourced from the Living Architecture Monitor
After a green roof design and installation training in Denver in 2017, my students and I had a special treat – we were able to visit the 10 year old modular green roof system that lies on the top of the Environmental Protection Agency’s (EPA) Region 8 headquarters. It’s the first time I’ve seen one of the first-generation modular systems, in this case a Green Grid system, after many years of wear and tear. It was holding up very nicely. The 19,840 square foot green roof is accessible to building occupants, features four inches of proprietary growing medium, and six species of drought tolerant sedum. It’s been the subject of plant research by Jennifer Bousselot of Colorado State University who focused on how solar panels on the roof impacted plant survival. There is a weather station that collects rainfall, temperature and other data, as well as a supplemental irrigation system that provides water during periods of drought. The plant coverage rises and falls depending on the season, and it was November when we arrived.
Back in 1969, Denver State Legislators created a quasi-governmental organization called the Urban Drainage and Flood Control District following some significant flooding events. This new body established water management goals regarding drainage and flood control over a 1,608 square mile area, which includes Denver and more than 2.8 million people. The stormwater retention goal is to retain the 85-percentile storm event, which in Denver averages out to a 0.6 of an inch precipitation event or less. Cities determine how the stormwater goals are to be met. In urban areas, buildings with more than one half an acre footprint, such as the EPA headquarters, are required to manage the 85th percentile storm event onsite. Typically, civil engineers have met this requirement by building large retention vaults for projects in urban areas, which take up considerable space in the basements of the buildings. The retention of stormwater onsite does not contradict Denver’s Water Law requirements for infiltration, as long as stormwater management technologies are allowed to drain within 72 hours of a rain event.