A green roof initiative passed by ballot in the City of Denver that will require developers of buildings larger than 25,000 square feet to include rooftop gardens or solar panels. Existing buildings will have the same requirement when they undergo roof replacement. The percentage of roof covered by a green roof scales by building size starting at 20 percent for 25,000SF buildings to 60 percent for greater than 200,000SF buildings. The green roof may include a combination of green roof and solar as long as the combination is at least 30 percent green roof and retains a specified rainfall volume.
The purpose of the measure is to reduce urban heat island effect thereby reducing the temperature in the city and some of the cooling load. Green roofs provide additional benefits of longer roof life, stormwater management, new microhabitats for nature and green space for tenants. Initiated Ordinance 300 will go into effect January 1, 2018. San Francisco, Toronto, Paris and London have mandatory green roof programs while Chicago, Philadelphia, New York City and DC offer incentives for green roofs. More information at Greenbuildingadvisor