Green Institute’s new rooftop is a vision of progress
by Evan Reminick
2004—On the roof of the Phillips Eco-Enterprise Center,
home of The Green Institute,
most of the surface that is not covered with solar panels is planted
with greenery. It’s an extraordinary sight not only for
visitors to the building but also for commuters by the thousands
who are whisked by daily on the elevated tracks of the Hiawatha
rooftop features not only the largest photovoltaic array in the
five-state area of Minnesota, Iowa, the Dakotas and Wisconsin, but also
the Twin Cities’ first green rooftop built specifically
to increase a building’s energy efficiency and manage stormwater
Krause, director of The Green Institute, said it was planned to
be a high-visibility demonstration project that could generate
useful data for designers, planners and academics.
riders get a close look at the green roof atop the Phillips
|Where the green part of the rooftop
ends, the 5-state area's largest photovoltaic array begins
are living proof that these progressive technologies can be built
around here,” said Krause. “We represent the next
generation of environmental thinking that it's not only the right
thing to do, it’s the smart thing economically. We’ve
taken the barren, unproductive space of an industrial rooftop
and put it to work to generate electricity and improve the drainage
of our entire property.”
Krause said that over the past several months he has given tours
to numerous local developers interested in green roofs and solar
energy. Most, he said, represent smaller-scale, high-density urban
as an advocate or consultant, The Green Institute has also
influenced decisions to install green rooftops on several
prominent buildings in the area.
These include Abbott Northwestern Hospital (installing a green
roof atop an old helipad), the new downtown central library now
under construction (committed to building a green rooftop), and
Minneapolis City Hall (studying a green rooftop for its inner
of green roofs
An ”intensive” green roof is created through the use
of planters, beds or pots. Intensive roofs are mainly decorative,
as with a typical “roof garden.” Intensive green roofs
may use plants with foliage from one to 15 feet tall and may require
several feet of soil depth, according to Emory
Knoll Farms, a grower of green roof plants in Street, Maryland.
“extensive” green roof is a working system planned
to manage stormwater, reduce heating and cooling costs, and extend
the roof’s lifespan. Extensive green roofs usually use plants
with foliage from 2 to 6 inches and from 2 to 4 inches of soil,
according to Emory Knoll Farms. Plantings for extensive roofs
are made directly atop the roof surface, with intermediary layers
of engineered soil and extra waterproofing.
|The Phillips Eco-Enterprise
Center's green rooftop features both "extensive"
and "intensive" plantings.
|Michael Krause, executive director of
TheGreen Institute (right) with board member Jeff Karr at
a recent open house celebrating the green rooftop.
The Green Institute’s green rooftop distinctively features
both extensive and intensive plantings. It was designed and funded
in part by The Kestrel
Design Group, Inc., of Edina.
Krause says that as a rule of thumb, green rooftops cost twice
as much as typical flat roofs to install (ranging from $14 to
$25 per square foot for an “extensive” roof) but last
twice as long (35-50 years for a green roof vs. 15-20 for conventional
Zoll, who directs The Green Institute’s GreenSpace Partners
program, said the 4,000 square-foot green roof of the Phillips
Eco-Enterprise Center cost about $75,000 to install. He said the
cost of installing both the green roof and the solar panels was
lowered significantly by an abundance of volunteer labor, a benefit
few developers can count on.
Zoll noted that living roofs require more maintenance, mostly
weeding, during the first years after installation, but that the
cost comparison evens out as time goes on.
Yet for green roofs—like other new building technologies
vying for market share—cost comparisons can be the weakest
selling point. Though their use is common in Europe, extensive
green rooftops are just taking hold the United States.
a result, demonstration projects like the Chicago City Hall and
the Phillips Eco-Enterprise Center here in Minneapolis remain
too few in number and too new in lifespan to generate the kind
of meticulous benchmarks most large developers require when costing
A case in point is the Midtown
Exchange, the ongoing redevelopment of the former Sears complex
in south Minneapolis. After being approached by The Green Institute,
the project’s developer, Ryan Companies US, Inc., conducted
two separate feasibility studies of green roofing systems, said
Mike Ernst, the project manager.
Ernst said vendors’ estimates for the installation costs
of green roofs were incomplete. Because of the size of the Midtown
Exchange project and the attendant financial risks, Ryan Companies
decided not to take the chance on green roofs. Ernst said that
Ryan Companies remains interested in working green roofs into
future projects that prove more suitable.
Zoll said the 10,000 square foot green rooftop on Chicago’s
city hall has yielded a $10,000 annual savings in air conditioning
Widespread application of green rooftops, he added, would greatly
reduce the “urban heat island” effect. Urban heat
islands occur when concentrated development produces significantly
higher (up to 10 degrees Fahrenheit in the summertime) temperatures
than occur in surrounding countryside, leading to increased energy
consumption, health risks and building maintenance.
|Visitors to the rooftop deck take in
|Green rooftops can help the region,
especially the downtown areas, reduce its trend toward becoming
an "urban heat island".
Heat islands are subject to regulation by the U.S. Environmental
Protection Agency. Krause said the Twin Cities are trending slowly
but predictably toward non-attainment of the applicable Clean
Air Act standards. He said government and businesses have estimated
the cost of meeting additional federal regulations at as much
as $250 million per year should the region reach non-attainment.
Under the building codes of most cities, each property must be
able to manage runoff from stormwater so that it does not spill
onto adjoining properties. Krause, who sits on the Minneapolis
Planning Commission, said most property developments must contain
15-20 percent of “pervious”, or water-permeable, surface
to offset the runoff created by impervious surfaces like driveways,
parking lots and normal rooftops.
Green roofs are so effective at containing runoff from buildings
that the Minneapolis planning staff has begun to offer a one-to-one
surface area credit against impermeable surfaces on the ground.
Thus, the installation of green roofs could grow to have great
applicability in commercial construction, particularly big-box
retail development, said Krause.
Working in concert with swales, ponds and other natural drainage
measures in high-density development, green rooftops could lower
the high cost of installing extensive sewer grids, Krause added.
Again, he pointed to an example close to home: the green roof
on the Phillips Eco-Enterprise Center is helping The Green Institute
to realize its goal of managing 100 percent of its stormwater
Zoll said green roofs will soon demonstrably lower utility bills
in Minneapolis. The city will soon begin to bill property owners
for stormwater utility fees according to the amount of impervious
surface on a property. Zoll said the city has an opportunity to
use this restructured fee to create incentives for property owners
to install green rooftops, rain gardens, parking lot green islands,
permeable paving and other on-site stormwater management features.