Denver voters passed one of the strictest green roof mandates of any city in the world earlier this month.
Initiative 300, passed with about 54% of votes cast, creates a new building code that requires vegetative roof systems or solar panels for most buildings 25,000 sf or larger constructed after Jan. 1, 2018. The measure is more stringent than other green roof codes because it also requires many existing buildings to be retrofitted with green roofs when a roof needs replacement.
Older buildings that cannot support the load of a vegetative roof can get an exemption. The measure is intended to help keep the outdoor air cooler, reduce stormwater runoff, reduce the amount of energy consumed by air conditioners, and, in the case of PVs, generate clean energy.
Opponents of the referendum were concerned that it would be costly and hurt nonprofits and affordable housing programs. Advocates conceded that green roofs cost more, but argued that they would pay for themselves in about six years.