Green Roofs and Water in the Western US

Written by Jennifer Bousselot, Assistant Professor; Colorado State University

Jennifer Bousselot is an assistant professor at Colorado State University in the Department of Horticulture and Landscape Architecture. Bousselot has studied green roof species selection, water use and substrates in Colorado for over 10 years. She is also coauthor of the Colorado Native Plant Society published third edition of Common Southwestern Native Plants.

Water in the western US is a matter of life or death, especially in the case of living architecture. Green roofs have been brought to the forefront in our region ever since the enactment of the Green Building Ordinance in Denver, Colorado. With green roof acreage on the rise in our region, questions about installation and maintenance are now quite common.

One of the major concerns is how to handle water. In most of the world, green roofs are designed without permanent irrigation, so they depend solely on natural rainfall. Here in the arid and semi-arid western US, we can go months at a time without precipitation. Therefore, permanent irrigation is an ‘insurance’ for the vegetation against extreme drought conditions.

If it is designed and applied correctly, irrigation application rates on green roofs can be very minimal – just enough to keep drought-tolerant and hardy plants alive during the hottest, driest times of the year. In fact, research at the EPA Regional Headquarters in Denver showed that we were able to maintain a healthy green roof by investing only 5 inches of irrigation a year, which is 5 to 10 times less than what it takes to irrigate a lawn in our region.

Energy savings, a reduction in the heat island, stormwater management, protection from hail damage, and the many other environmental, social, and economic benefits of green roofs far outweigh the small investment of water that they require.

Learn more about Green Roof and Wall implementation in Colorado at the Colorado Living Architecture Seminar on August 9 at University of Colorado Denver - register today!