Green roofs sprouting up in Colorado
The Rocky Mountain Independent is running a three-part series of environmental snapshots from the Front Range. Part three examines the growing trend of green roofs.
The green roof movement in Denver is starting small, and it’s not just green — it’s red, orange, yellow and purple, too.
Rainy cities such as Portland and Chicago have embraced green roofs with gusto. Building owners there have learned that a layer of soil and plants can keep heating and cooling costs low. Plus, every downtown resident benefits from cleaner air and cooler summer temperatures.
But, as Colorado gardeners know, it’s not as easy to grow plants in the semi-desert of the Front Range. A few buildings have installed green roofs, but Denver’s only publicly accessible one is above the café at the Denver Botanic Gardens.
“Green roofs are a really exciting technology that’s been around 40 years, but no one has built them in an environment like ours,” said Andy Creath, owner of Green Roofs of Colorado.
The trend is starting to take off, though. Creath said he has been busy with installations for private homes in Denver, Boulder, Vail, Steamboat Springs and Aspen, plus buildings at Colorado State University and Fort Lewis College.
But architects have to learn a lot about rooftop gardens in this dry climate. Mark Fusco of the Denver Botanic Gardens said he hopes the roof he manages will help Coloradans figure out how to do it right.
The Botanic Gardens’ roof stays true to the xeriscape ethic pioneered in Colorado, with drought-tolerant native plants such as succulents, cactuses and a rainbow of flowers. The roof has rocks instead of turf between the plants, and there’s a method to the design, Fusco said.
“We haven’t just slopped a bunch of soil up on top of the roof and planted some plants and hoped it worked out,” he said.
A green roof requires a waterproof membrane on the bottom, then layers of rock and soil to shed water from downpours while retaining enough to nurture the plants. A good green roof should reduce storm-water runoff dramatically, and the Botanic Gardens’ roof proved itself during Denver’s heavy rains this spring.
“Absolutely fantastic. We haven’t had a single issue,” Fusco said of the runoff.
The roof has 50 different species of plants that gardeners are testing to pave the way for other green roofs along the Front Range.
“It has really broad implications for how green roofs can be built here in Colorado,” Fusco said.
Others are starting to notice. Last month, the Botanic Gardens held a green-roof symposium, and 170 people attended.
Green roofs tend to cost twice as much as a regular blacktop roof, Creath said. They can be as cheap as $10 a square foot or as much as $40 a foot for deep soil with a variety of plant types. But they will pay for themselves in lower energy bills and also last almost three times longer than regular roofs.
That’s because heat, not moisture, damages roofs the most, Creath said. A blacktop roof can reach 170 degrees in Colorado’s summers, flexing and expanding the roof membrane, he said. A green roof, meanwhile, will stay close to the ambient air temperature.
If enough buildings installed green roofs, it could reduce the urban heat-island effect, Fusco said.
Fusco is working with Mayor John Hickenlooper’s office on policies to encourage green roofs in Denver. Other cities have started programs with pilot projects, then followed with incentives. New York, for example, offers tax breaks based on the square footage of green roofs, Fusco said.
Some local landscape architects are so enthusiastic about the idea that they volunteer at Creath’s business in exchange for training. Creath knows he might be training his future competition, but he said he welcomes the company in the fledgling industry. He’s eager to see how architects adapt green roofs to Colorado.
“They have beautiful visions of what you can do on a roof,” he said.
Part one: Summer’s wet start a mixed blessing
Part two: Uranium poised for another boom