- Denver Mayor Michael Hancock has come out in opposition to a city green-roof measure that, if passed, would require that new buildings of 25,000 square feet or more be outfitted with at least 20% green roof and/or sustainable features, according to Denver7 News.
- The type of green or sustainable features required — solar panels, living gardens or both — would depend on the building's size. Buildings 25,000 square feet or more undergoing a roof replacement could also be required to comply with the new rule.
- In a letter to some city council members, Hancock said the "mandate-only" green-roof legislation did not offer enough incentives or options to building owners, would increase costs of installation and maintenance, and was not developed in the spirit of collaboration — an assertion that the authors of the bill deny.
Green roofs typically fall into one of two broad categories — intensive and extensive. A system of low-lying, low-maintenance plants, which create a relatively light roof load, characterizes an extensive roof. The intensive roof has trees, shrubs and architectural features, like the 9-acre green roof included in Facebook's Menlo Park, CA, campus. Both types use a waterfront membrane as its base and are typically installed on flat roofs.
Green roofs absorb rain, so they can reduce the amount of stormwater runoff into city sewer systems. They also help insulate a building, helping to save money on energy bills. According to the U.S. Environmental Protection Agency, other benefits include the creation of new habitats for birds and other species, carbon sequestration and storage and mitigation of the urban heat island effect.
In 2009, Toronto was the first North American city to enact green-roof legislation. San Francisco was the first U.S. city to make green roofs mandatory for most new building projects with a requirement that 15% to 30% of the new roof space include solar, green roofs or a combination of the two.
Green Roofs for Healthy Cities released its 2016 Green Roof Industry Survey this past July and found that the green roof industry in North America had year-over-year growth of more than 10% from 2015. Survey respondents reported more than 4 million square feet of green roofs installed in 2016, which translates to almost 47 million gallons of retained stormwater and 6.03 million saved kilowatt hours, as well as the creation of more than 1,600 new construction and maintenance positions.