In the days of Laura Ingalls Wilder, folks traded in a sod roof for shingles as soon as they could afford to. The reverse seems to be happening now, as homeowners trade shingles for sedum, even though they can’t necessarily explain why they did it.
Joe Wild Crea built his new garage to accommodate a green roof because “it made sense to me.” Mary Mergenthal put a green roof on the newer, flatter additions to her home after her grandson suggested it. Diane Norris thought it sounded “fascinating,” so she attended some meetings sponsored by the Capital Region Watershed District and persuaded her husband, John, to build their new garage to support vegetation.
The Watershed District recently announced a fresh round of grants to homeowners and organizations for installing green roofs, rain gardens and other water-protection projects. Information can be found at the St. Anthony Park Community Council Web site: www.sapcc.org.
What’s so great about putting plants on your roof?
According to Roofbloom, an organization encouraging Minnesotans to green their roofs, the benefits of green roofs include reducing wear and prolonging the life of roofing materials; reducing heating and cooling costs (not only by insulating but also by cooling through evaporation in summer); reducing stormwater runoff (a roof can absorb as much as an inch of rain) and cooling the water that does run off into sewers and creeks; improving air quality; mitigating climate change, specifically the “urban heat island” phenomenon; adding to urban green space; and providing habitat for birds and insects.
And, of course, the roofs can be beautiful. Ivan Swenson, of Swenson’s Workshop, designed and installed Mergenthal’s roof. In addition to all the environmental benefits, “We wanted it to look cool from the street,” he said.
On all three St. Anthony Park roofs — Mergenthal’s, the Wild Crea family’s and the Norrises’ — sedum prevails, sometimes mixed with grasses or a few other prairie natives. Already the young transplants show off a rainbow of shades in stems and leaves, and as they fill in, the roofs will become carpets of blended color.
Unlike the sod roofs featured in pioneer tales, roots don’t dangle from the ceiling under today’s green roofs, which are installed atop a watertight membrane, a root barrier and insulation. Over that goes a drainage layer, a filtration system and a pumice-based growing medium that’s lighter than dirt and carefully balanced with just enough organic matter to keep desirable plants alive without encouraging weeds.
It’s not a job to be done in a weekend, at least not until more contractors get comfortable with the systems. All three projects took one summer of construction and the next spring to finish and plant, and that was after a year or two of research.
One possible surprise awaits in the city’s permitting process. Swenson said that while the city treats a green roof as a heavier load, requiring beefed-up structure, “it weighs less than shingles do.”
Wild Crea said when he applied for a permit to build a new garage, the city took one look at the green roof idea and sent him back to the drawing board, this time insisting on a structural engineer’s imprimatur.
Jim Bloom, building official and senior plan examiner for the city of St. Paul, said the city treats a green roof on a garage the way it might treat a second story or any other deviation from the typical two-car garage.
“If you go to an alternate design,” he said, “we’re going to ask for a second drawing,” unless the original demonstrates a clear understanding of the adjustments that need to be made for load, stability and other concerns.
So Wild Crea hired an engineer, who took the green roof’s recommended pitch and the expected load of the materials, ran it through the usual formulas and sent Wild Crea back to the city with a successful proposal.
“They’ll learn a little bit too,” Wild Crea said of the city’s permitting process.
Wild Crea also contracted out the structural work, up to and including the roof membrane. “That’s just a black rubber roof that you’d see anywhere,” he said, but it’s not a job for an amateur. He hired an experienced roofer to put it on.
He added the layers that would make the roof “green” and ordered plants from Gertens: 1,600 of them to cover 840 square feet of roof.
Then came the fun part. He decided to make a neighborhood project out of it, so he typed up an invitation to anyone wanting to help finish the roof and posted it on several e-mail lists.
“It was so much fun,” he said a couple of days later. “I’m still pinching myself.” He guessed about 50 people came to help, and when there were problems getting a rented conveyor belt started, folks loaded planting medium in buckets and started passing them up the ladder.
“They bucketed up more than we got with the machine,” Wild Crea said.
The crowd included lots of kids, he said. “That was the best part — the kids that were here. They got to climb ladders and play in the dirt.”
John and Diane Norris did a lot of improvising on their project. John works in industrial salvage, and Diane sometimes goes along with him to job sites and gathers discarded plants. A steel beam down the center of the garage formerly supported the air conditioning at a large hotel, and there’s insulation from a 3M building in Shakopee.
“Eighty percent came from what I already had in the yard,” Diane said of the sedum, day lilies, herbs and prairie plants collected over the years and recently relocated to the garage roof. Because she didn’t have to buy many plants, their $1,200 grant from the Watershed District covered the majority of the roofing project.
The Norrises will also install a patio area on the garage roof, which looks out on the commercial area of Como Avenue between Carter and Doswell. A few containers hold more plants. “It’s a nice green area that you can sit up on the deck and look at and just enjoy,” she said.
Mergenthal’s project is the most ambitious, both in terms of space (about 1600 square feet over three areas) and because part of her project is over the addition to her kitchen. She doesn’t just park her car under those layers of soil; she sits under them for breakfast, lunch and dinner.
Hers is also the only project that draws the full green-roof benefit of energy conservation, because she has central air conditioning that gets a big boost from the extra insulation and evaporation.
She said her grandson Jennings, then six years old, called her four years ago to propose the project. “He said, ‘My dad and I have been looking online at green roofs, and we think you should do it,’” Mergenthal recalled.
The more she thought about it, the more it seemed a fitting tribute to her husband, recently deceased, for whom the grandson had been named. “He was a great gardener,” she said of her husband.
Like Wild Crea, Mergenthal started her research by visiting the environmental building at the State Fair.
She approached Swenson because even though he’d never done a green roof, she trusted him. “I’ve nothing but gratitude for all the subcontractors I’ve gotten through the Swenson brothers,” she said.
Mergenthal is active in rural land protection and thought first of native prairie plants, but the prairie nurseries she knew and loved turned her down, reminding her that one reason those plants survive in a harsh climate is their deep root systems, which would be inappropriate on a shallow rooftop.
So she turned to Bachman’s, where Doug Danielson at the Lakeville site recommended sedum. She said she’d always thought of that as a pesky invasive, “but creeping things are good in the right place.”
Swenson said his business connections helped him get good deals on materials for Mergenthal. Still, he estimated the project would be about three times as expensive as a traditional roof.
“It’s a system, not a roof,” he said.
“It was a great experience,” Swenson added. “I hope to do hundreds more. But people have to understand what the purpose is, what they want from it.”
And once the project is “finished,” there may be more expenses coming, he pointed out, as plants will probably die and need replacement. The roof will have to be weeded, and varying sun exposure may affect how well the plants do. And it may need watering, although all three homeowners expressed surprise at how well their plants had tolerated the unusually dry month of May.
Mergenthal and Wild Crea both have rain barrels and plan to pump water from those back up onto their roofs. Wild Crea also has rain gardens to solve some drainage problems around the house and garage.
Wild Crea said green roofs are common in parts of Europe, and he hopes the idea catches on here. “In 15 years, maybe it won’t be so new,” he said.
Asked by a visiting five-year-old why she had plants growing on her roof, Mergenthal boiled it down to the simplest terms.
“They’re going to make my house real cool,” she said, “and they’re going to look pretty and they’ll put good things back into the air.”
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