Mayor Michael Hancock opposed the Denver Green Roof Initiative but said Wednesday, as votes still were being counted, that his administration was taking its probable passage to heart.

“We have always made a good-faith effort to implement the initiatives — once the people have spoken, that’s our job,” he said.

Hancock was joined by City Council members in saying they would respect the will of voters as some officials rushed Wednesday to get their arms around a voter initiative that, if certified, would give Denver the most stringent, far-reaching green-roof mandate in the nation at the start of next year.

Denver officials’ race to grasp all implications of the initiative — which would apply to most larger new buildings and some existing ones when their roofs are replaced — could include its effect on the city’s big win Tuesday night: its $937 million bond package.

As of Wednesday afternoon, the green-roof mandate — on the ballot listed as Initiated Ordinance 300 — was polling at 52.5 percent support.

“Let me very clear: We’re not looking for legal challenges,” Hancock said, speaking to reporters at a news conference in the City and County Building that was staged to celebrate voters’ approval Tuesday of all seven components of the bond package. “We’re making sure that the path to implementation of Initiative 300 is clear — and that we understand all of the possible opportunities and challenges that might be inherent in implementing the initiative.

“So it’s about doing what the people have asked us to do on this initiative.”

2017 Results Green Roof Initiative

But leaders of the opposition campaign, called Citizens for a Responsible Denver, were keeping legal options open Wednesday.

Kathie Barstnar, the executive director of the state’s commercial real estate development association, expressed disappointment in what she considered the clear outcome of the vote. She said the opponents were considering possibilities such as sharing concerns with city officials or looking for ways to challenge the initiative in court.

After the Green Roof Initiative’s backers were successful at qualifying the measure for the ballot, Hancock joined building and real estate interests in opposing the measure — saying it “goes too far too fast” — despite lauding its goal of more rooftop gardens.

But most voters appeared to like the idea of the mandate.

The most recent results, released at 3 p.m., showed the initiative winning by a margin just shy of 5 percentage points, which has widened with every release of results. More than 105,000 votes have been counted, but potentially 25,000 or more remained to be processed, based on ballot-return data from the secretary of state’s office.

The Denver Elections Division plans to update the results next at noon Thursday and to finish counting later in the day, spokesman Alton Dillard said.

Organizer hopes to “start a dialogue”

Brandon Rietheimer, a 30-year-old environmentalist and Red Robin restaurant manager, served as the initiative’s campaign manager. He said he planned to reach out to the mayor’s advisers and council members in coming days “to try to start a dialogue and increase the educational aspect of things.”

“There were a whole bunch of falsehoods thrown around,” he added, referring to the initiative’s potential costs and effects on development.

At its most basic level, the new green-roof requirements will mandate that builders incorporate rooftop gardens, potentially in combination with solar panels, when new buildings have at least 25,000 square feet of gross floor area underneath.

The requirements also would be triggered for existing buildings of that size when their roofs are replaced or additions push the floor area above the threshold — a key way that the initiative goes further than even San Francisco, which began enforcing a green-roof mandate at the start of this year after three years of discussion.

Rietheimer conceded that some aspects of the new 16-page ordinance that would be enacted by the initiative’s passage could use clarification.

For instance: “The intention was for existing buildings to have some more wiggle room than new buildings,” he said.

Hancock: Initiative may add costs to bond projects

The slew of city-supported construction projects that Denver’s new bond package will set in motion was among Hancock’s concerns as he addressed the Green Roof Initiative.

“We are concerned that it may mean additional costs to some of these projects that we are laying out, in terms of the bond, that we didn’t have programmed in the dollars,” he said.

The mayor said it was too early to elaborate on other concerns expressed by the city attorney and other advisers at a closed briefing earlier Wednesday.

But he did raise the possibility that the City Council or the administration could consider “tweaks” as they work out implementation. Six months after passage, the city charter grants the council the power to make changes to a voter-passed initiative, or repeal it entirely, with a two-thirds majority.

Councilman Kevin Flynn, who opposed the initiative, said the council should avoid stepping in to thwart voters’ intentions. His concerns centered on the green-roof requirement applying to roof replacements for large buildings, which he said could make a standard replacement much costlier — especially for shopping center owners in his southwest Denver district.

“If there are unintended consequences down the road, they need to be worked out with the proponents,” Flynn said.

The results so far have shown that voters who waited to turn in ballots on Election Day — and are more likely to be younger — were more supportive of the Green Roof Initiative, explaining its steadily growing lead.

Initial results at 7 p.m. Tuesday, which reflected ballots turned in through Monday night, showed 51.2 percent of those voters in support. But support increased — to 56.1 percent — among the 27,000 voters whose ballots were counted later and reported in subsequent releases through 3 p.m. Wednesday.

Rietheimer’s group faced an opposition campaign, led by Barstnar and members of the Colorado Real Estate Alliance, that raised 12 times as much money. What the initiative backers could spend went mostly to Facebook ads, Rietheimer said.

“It feels good to beat a quarter-million-dollar opposition budget,” he said Wednesday.

How the Green Roof Initiative works

The green-roof coverage requirements would start at 20 percent of the roof area and ratchet up to 60 percent, depending on a building’s total square footage and type. It also sets out construction standards.

The initiative exempts residential buildings of four stories or less. It also allows the city to grant exemptions when green-roof components aren’t feasible — as long as the building owner or developer pays an opt-out fee that amounts to roughly the cost of putting one in.

The new ordinance would take effect Jan. 1, with an exemption for developers who submit complete building permit or site plan applications to the city’s planning department before that date. That probably would spark a December rush to the permit office.

Hancock recalled telling the Green Roof Initiative’s backers that “our values were aligned,” despite his opposition. “We’ve been working on the issue of (environmental) sustainability since we came into office,” Hancock said Wednesday.

But his administration’s desire for a “collaborative” approach prompted city officials last year to resist the idea of a green-roof mandate.

So Rietheimer and other organizers decided to go straight to voters.

The initiative’s backers say green roofs can reduce Denver’s urban “heat island” effect from heat-radiating roofs and pavement that, according to one study, is the third-largest among U.S. cities.

And they argue that cost concerns from the building industry are overblown, since rooftop gardens and solar panels pay for themselves in energy savings over time.

Denver developer Kyle Zeppelin, a supporter of the initiative, has been incorporating rooftop gardens and solar-energy generation into his developments’ roofs in recent years.

A green roof often spurs a more interesting building design without too much more expense, he said in an interview before Election Day.

“It’s more cost than the most basic form of a building,” Zeppelin said. “But when you’re comparing it to really expensive finishes or architectural systems, it’s not that much more cost.”