The days of sprawling black roofs in Denver may be ending — but they won’t go quietly.

The Denver City Council will decide Monday whether to create a “cool roof” law for the city. The big hope is that requiring reflective, light-colored roofs on large buildings would lower ambient temperatures, fighting back against the city’s heat-island effect.

“It’s not groundbreaking in Denver, but it’s one of the biggest” of the new cool roof laws, said Kurt Shickman, executive director of the Global Cool Cities Alliance. “They’ll join a small number of big cities.”

The change would affect new construction and reroofing projects for buildings over 25,000 square feet — not your typical home renovations. The new law also would force affected property owners to choose between creating green space, installing solar panels and saving energy.

And, for once, many developers are looking forward to a new rule: It would replace the “green roof” law that voters approved last year, which would have required more costly rooftop gardens. The proposal has the support of green-roof organizer Brandon Rietheimer.

Roofers vs. reformers

But even this smaller change has put the city in the middle of an ongoing debate between roofers and reformers. The council on Monday is likely to hear from industry representatives who say that the cool-roof mandate is an oversimplified approach for a complicated problem.

“Mandating a single component of a roofing assembly is just not what is good design practice,” said Ellen Thorp, associate executive director of the EPDM Roofing Association, which represents manufacturers of EPDM, a rubber membrane for roofs.

The trade association argued in a letter that cool roofs can cause two major problems in colder climates like Denver’s. First, they can purportedly accumulate moisture. Second, they are meant to retain less heat, which means heating bills can be higher.

“Some of the best roofs on the market really were not going to be allowed, period,” said Jeff Johnston, president of the Colorado Roofing Association, who says that much of his Steamboat Springs business is still focused on dark roofs. “Why eliminate it?”

Attempting to adapt

The reason is simple, according to Katrina Managan, the city staffer who coordinated the roof revision.

“The reason to do them is to adapt to climate change,” she said. Denver could see a full month of 100-degree days in typical years at the end of the century, according to projections from the Rocky Mountain Climate Organization for a “high” warming scenario.

And the impact will be worse in urban areas, where dry, unshaded rooftops and pavement are baked by the sun and heat the air around them. Urban environments can average up to 5 degrees hotter than the surrounding rural areas, and the difference can be much greater at times, according to the Environmental Protection Agency.

Cool roofs address part of that problem: They reflect the sun’s energy away and stay up to 60 degrees cooler than traditional roofs, the EPA reported.

“It will save Denver a tremendous amount of money. It will create a huge amount of benefit through cooling. And it will set the example,” Shickman said. “It really does add to the argument that says we really should be considering this for almost all of our big American cities.”

City research found that the cool roof mandate would be more effective than the green roof initiative in combating heat, since the green roof requirement only covered parts of rooftops.

The bottom line?

Major cities began adopting cool-roof requirements nearly 20 years ago, with northerly Chicago among the first. It’s been joined by Philadelphia, Baltimore, New York City and Los Angeles, among others, according to GCCA. Much of the southern United States is now covered by the requirements, and San Francisco in 2017 adopted the first “green roofs” requirement.

“We’ve been in an epic fight between the industry and those of us on my side who are trying to push this forward,” Shickman said.

Thorp, the EPDM Roofing Association representative, pointed to research to argue that Denver should proceed cautiously. Because cool roofs don’t get as hot, they can accumulate more condensation, which requires specialized designs to combat. And she said that a cooler roof could mean higher heating costs and thus more carbon emissions in colder Denver.

She acknowledged that the law would hurt sales of EPDM: Competing materials are cheaper and more popular for cool roofs. But she said that her clients also make those other materials.

“They’re going to make the sale one way or another,” she said.

Shickman countered that the companies are more heavily invested in EPDM, and therefore have a financial motivation to lobby against cool roofs. Other materials “have been eating the lunch of EPDM,” he said. Thorp declined to disclose sales figures for the companies, but said the organization’s “primary driver” was to give roofers options.

Cool roofs are already popular

A city poll of roofers found that about 70 percent of new roofs in Denver are “cool.”

“What we’re tending to find is most companies now are wanting to go to a light roof,” said Scott Nakayama, director of operations for Denver-based North-West Roofing. “The amount that they’re going to save, as far as heating and cooling bills, tends to stand out.”

His company has been installing about 20 light-colored roofs per year, and hasn’t encountered any of the issues raised by the EPDM Roofing Association, he said. Shickman points to this apparent lack of complaints as evidence that a well-designed cool roof can avoid moisture and other issues.

They do come at a cost premium: Cool roofs can cost about 1.5 percent more than a traditional roof, according to city-commissioned research by Stantec, the engineering company. Thorp said that estimate is too low.

If the law is approved, it could take several years before it starts to have a regional effect, since roofs generally only need replacement every 20 years.

The rest of the details

Under the change, developers of new builders can choose among the following options.

Install green space on the building or on the ground.

Pay for green space somewhere else.

Install renewable energy or a mix of renewable energy and green space.

Design the building for 12 percent energy savings compared to city standards, or achieve 5 percent savings plus green space.

Achieve either LEED Gold or Enterprise Green Communities certification for green design.

Existing buildings will have similar types of options, with different details.