The Denver Green Roof mandate will put more green atop city buildings, but might end up leaving less green in schools.
The mandate, which becomes effective January 1, 2018, requires a roof garden or a combination of a green roof and a solar energy collection system on every new building with a gross floor area of 25,000 square feet or more. By comparison, a large supermarket is around 40,000 square feet while a super-center is approximately 250,000.
Unique in its range, the mandate also includes building additions or roof replacement of existing buildings.
“It is supposed to be a lot, because we are doing something different here. We are trying to incorporate existing buildings. We know that there is a challenge with that, but nobody else does existing buildings so that would really increase the amount of acreage that we see [of roof gardens],” said Brandon Rietheimer, head of the Denver Green Roof Initiative.
Over 3,000 existing buildings would be affected by the mandate, according to Rietheimer. Together with the new buildings, the green roof area in Denver will add up to “something crazy” like 550 million acres, he said.
But not everyone sees Denver roofs coming up roses.
“We are estimating that that cost will be something about three times as much as a traditional roof,” said Katie Kruger. She is CEO of the Denver Metro Commercial Association of Realtors and member of Citizens for a Responsible Denver, a coalition of Colorado businesses that campaigned against the mandate.
A green roof is indeed more expensive, admits Rietheimer. In general, „it’s two and a half times more expensive than a traditional roof,” he said. But supporters hope that the costs will decrease when the higher demand brings more industry and more competition that drives the costs down.
Cleaner air, a less hot city, less pollution, better storm water management, increased biodiversity and a better overall life quality are the proposed benefits of green roofs.
„I think esthetics is first and foremost the obvious benefit. The other stuff just gonna takes some time,” Rietheimer said.
The other stuff includes less energy consumption – less air conditioning in the summer and less heating in the winter – and thus lower energy bill. The decrease in air-conditioning due to a lower average city temperature is a huge benefit, according to Rietheimer.
Green roofs don’t absorb the sun like black roofs do, so they pass on less heat into the buildings below them.
“Right now, our traditional black roofs, they just absorb sun and heat all day, every day. And then that retains that heat into the night. So, you have a warmer evening period, now you have to cool your building down even more, when it is dark out,” explained Rietheimer.
Plants instead release humidity by evapotranspiration, a photosynthesis process, and therefore act like swamp coolers, which creates more even temperatures. The difference is huge. “The EPA roof was 80 degrees ambient temperature in the middle of July. And across the street, at the Alliance Center, their roof was 170 degrees,” said Rietheimer.
On the other hand, Kruger said that according to her experience, even green companies recommend against green roofs. “Most of them would say ‚Don’t do the green roof‘. That’s what they told us. The green roof is expensive. In Colorado its really, really hard to keep the plants alive.”
She refers to the EPA building, which indeed struggled with dead plants and other expensive disadvantages, according to the EPA’s 2010 Fusco Justification Report. Richard Mylott, Public Affairs at the EPA in Denver, added that „the system requires regular maintenance and calibration of the irrigation system, as well as resoiling and replanting of the trays.“
Therefore, green roof owners have to keep the costs for watering and constant maintenance in mind. Not only substituting plants and soil on a regular basis but also the deteriorating tiny lines for the irrigation system.
The mandate does not dictate a certain plant species. But a maintenance plan is required that proves the well-being of the plants over a time period.
„Typically buildings do succulents, mainly, because it is cheaper,“ Rietheimer explained. „Honestly, you can do whatever you want. It’s really how much do you wanna water them?“ he added. Trees for example would be impractical, because they need more water and a soil depth of around 6 feet, said Rietheimer. Plus the structural foundation has to be stronger in order to hold the heavier load.
Speaking about maintenance, Rietheimer also mentioned the financial benefit of green roofs. Heating and cooling leads to constant contracting and expanding of the roof’s waterproof membrane. This makes the roofs susceptible to puncturing damages, for example, by workers dropping tools – or hail. According to Rietheimer, this is the number one cause for leaks.
“With a green roof that membrane is now protected through a couple of layers and then plants on the top. You are not getting that heating and contracting, you are not getting hail damage, you are not getting workers puncturing it. And that’s why they last two to three times as long,” he explained.
The higher maintenance costs for green roofs that Kruger predicted could therefore eventually be compensated by a longer lasting roof.
But there are more concerns.
„The issue in where it impacts schools is that it was really designed as a one-size fits all mandate. It is a requirement and no one is exempt,“ said Kruger, „And so, a hospital, a school, the Convention Center. Every single building, every single education facility will need to come up with the funding for a green roof.“
And there are not also the costs for the roof itself, she explained: “Some of our older buildings, they structurally have to be bolstered to be able to hold the roof-top.”
She fears that in some cases, the costs could be as high as a million dollars.
Of course, the mandate allows exemptions, Kruger said. “But those exemptions come with fines.” She assumes that most of the school buildings are either structurally not strong enough to hold a green roof or they are not appropriately oriented to the sun to draw enough solar energy. “We can guess that – most of our buildings are too old for that, they won’t be able to do that – all of our school buildings are going to be paying an exemption fine essentially to the Office of Sustainability.”
Which in the end would mean that taxpayers’ money intended for the school system would pour into the city’s pocket.
Exemptions could also discourage investors: “The problem with not exempting everyone is, if you leave something like new structures to have to bear the brunt of all these regulations, they might say, we not gonna built here anymore, we are not gonna bring our cool new schools here.”
Speaking about schools, Rietheimer said, it is more a scare tactic. “We don’t really think that is an issue. Typically funds for education are separate from funds for building improvements and construction. They typically don’t intertwine.” Rietheimer said, he has not heard any complaints from schools about that.
Also, the schools’ curricula could benefit from green roofs as the Calhoun School in New York City demonstrates. Opened in 2005, the roof is designed as a functional outdoor space and has been inspired a lot of studies and research among the students, said Beth Krieger, Director of Communication at the Calhoun School. Plus, the school’s lunch program benefits from the food that is grown on the roof.
Krieger explained that it was a learning process to discover what grow and what doesn’t. The school saw unexpected costs for planting and replanting, but they also saw savings in heating and cooling costs. In the end, she said the school didn’t regret installing the green roof.
“I think people ultimately see it as a good thing,” said Rietheimer about the Green Roof mandate. “There is gonna be some challenges. It’s new to people, so they don’t fully understand, but I think, once people realize and see all the benefits, they’ll come around.”
They hope to improve the mandate together in the future, said Kruger. “We are working as hard as we can to look at all our options and do what we can to make sure people don’t get hurt here.”
It’s still uncertain how the mandate will work out for Denver’s schools.
Brandon Rietheimer: I am sure, you have driven around and seen signs that are like „Ozone warning, don’t drive today“ and things like that. We are 11th worst in the nations for our ozone.“
VO: Air pollution was one of the main reasons for Brandon Rietheimer, head of the Denver Green Roof Initiative, and others to vote for the Green Roof Mandate in Denver last Tuesday. But what does it mean to have a green roof on your building? I spoke with Kevin Seiler, facilities director at the Community College in Denver about their green roof. The college’s main building, the Confluence Center, was designed with a green roof in 2011.
Kevin Seiler: There is a membrane that covers the entire building to protect … to keep the water from going past that. Then there is a tray system, you know, when there is too much water it moves that water off the roof. And then there is different medium depth built up for the plants to be. So it is about a foot thick, overall, from the roof membrane to what you see here, the gravel.
VO: According to Seiler, a green roof definitely needs more maintenance. I asked him what difficulties their roof met.
Kevin Seiler: In about year three, we’ve had … we developed some leaks and there was … there were some patches … There was damage done, during the construction to the roof membrane. We’ve had the irrigation system freeze a couple of years ago. This year we had problems with the irrigation either not working properly or overwatering, so it actually flooded the roof.
VO: A good water management especially in Denver’s dry climate is essential for the plants. The Denver Community College mainly planted grass. A special type of grass.
Kevin Seiler: But these type of grasses can go dorment, when it is a drought type condition. So most of them have sprung back, once we got the irrigation working. It is an area that staff and students do like to utilize and come out here and study, relax, eat some lunch. You have some great views up here above the city and the Front Range. So it is a nice space for people to hang out.
VO: The mandate will bring more than 3,000 green roofs to Denver. Which hopefully will create better living conditions, including better air. Both, proponents and opponents have to sit together and talk about the details of the mandate. But Katie Kruger, member of Citizens for a Responsible Denver, a group opposing the mandate, is hopeful.
Katie Kruger: It was an unfortunate start to such a wrapped up initiative in our state, but I think we could maybe get back to that yet, a collaborative way of doing it right. That’s our hope.