Most Like the Idea of Green Roofs — Including Critics of a Denver Initiative — But Should the City Force Builders to Include Them?

Ballot measure aims for rooftop garden or solar requirements to reduce urban “heat island” effect

A Denver initiative on the November ballot seeks to sprout more trees, shrubs and even vegetable gardens atop larger buildings across the city, a move that would accelerate a trend that has been embraced by some developers.

But by proposing a mandate on so-called “green roofs” that in some ways would stand as the nation’s most stringent — leapfrogging San Francisco — the local environmental activists behind the Denver Green Roof Initiative could be taking a gamble on Denver voters, observers say.

The tension between the clear environmental benefits of rooftop gardens and an aversion by some voters to wide-ranging government requirements was clear in a recent comment by Denver City Councilwoman Mary Beth Susman.

“You know, I think it would be great if we all had green roofs,” she said last week during a council review of the initiative with its backers and opponents. “They’re so lovely. But the mandate is what worries me. … If you have so much support for it, then why wouldn’t the market just take care of it?”

Initiative 300’s backers say they’re optimistic that voters will see the value in making rooftop gardens a standard feature of most new structures of at least 25,000 square feet in Denver.

“People love the idea. We have all these flat roofs with all this space, and we’re not doing anything with them,” said Denver resident Brandon Rietheimer, the initiative’s campaign manager. “Why aren’t we putting solar or green vegetation up there? … We hear all the time that Denver is an environmentally friendly city, yet we rank 11th for air quality and third for heat islands.”

Their goal, in part, is to address Denver’s status in a 2014 study by Climate Central, a scientific advocacy group, of having the third-greatest urban “heat island” effect produced by all the radiating rooftops and pavements. Only Las Vegas and Albuquerque ranked higher.

Builders could also incorporate solar panels to offset some of the initiative’s rooftop garden coverage requirements, which would start at 20 percent of the roof area and ratchet up to 60 percent, depending on the structure’s total square footage and type. Residential buildings of four stories or less would be exempt.

City officials would have discretion to grant exceptions — although a building’s owner would have to pay an opt-out fee based on what would be spent to build a green roof.

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