Chicago now has more buildings with green roofs than perhaps any other place in the country. The roofs have even begun to appear on residential projects like Washington Park, a 63-unit affordable housing project being developed by East Lake Management & Development Corp., based in the city.
A green roof – also known as a prairie roof, an eco-roof or a vegetated roof – is a waterproofed rooftop that has been insulated, covered with a layer of soil and then planted.
Flowers and hardy grasses sprout from the tops of many Chicago rowhouses and high-rises, including City Hall. Builders in Chicago have already finished or are now building green roofs totaling more than two million square feet.
More are on the way. Green roofs are required on any building that receives financial assistance from the city in its construction. In addition, the city offers projects that include a green roof the chance to build greater density and receive a $5,000 grant to help with the planning and installation of the roof.
Green roofs are expensive, but they help solve an even more expensive problem with storm water. Like many cities, Chicago has a combined sewer system that tends to overflow during heavy rains. But the Environmental Protection Agency is pressuring municipalities like Chicago to solve that problem. Just last May, Chicago announced a new $16 million tunnel designed to move rain water into Lake Michigan.
Many densely developed cities have problems like Chicago’s and may soon follow Chicago’s lead with incentives and regulations. For example, Washington, D.C., may have to pay $1.9 billion to dig three massive underground tunnels to store rain water to keep the city’s combined sewers from overflowing. Seattle and Portland have struggled for years with their heavy rains and require extensive storm water management at new developments.
Green roofs can drastically reduce these problems. A typical green roof can soak up more than half of the rain that falls on it in a year, so that the water never makes it into city sewers, according to the Chicago Department of Planning & Development (DPD). Even better, the rain that does flow off the roof flows more slowly, so that sewers are less likely to flood.
Green roofs are costly
Without subsidy, green roofs rarely financially benefit the developers who put them on their buildings. Instead, the benefits of green roofs help the whole community. Because of this, developers rarely install green roofs unless they are required to or are subsidized by local officials.
For example, in New York City the Battery Park City Authority has mandated that 75% of the roofs in its small neighborhood be planted and open to the residents.
With that requirement in mind, builders have grown green roofs on three apartment buildings in Battery Park: Tribeca Green, developed by The Related Cos., and the Solaire and the Verdesian, both developed by the Albanese Organization, Inc. A fourth green roof is planned for the Millennium Tower Residences, a sustainably developed condominium project developed by Millennium Partners, which will open this year.
A typical green roof costs about twice as much to purchase and install as a conventional tar roof, ranging from $8 all the way up to $24 a square foot with an average cost quoted at about $10 to $12, according to DPD. For comparison, a conventional tar roof costs just $4 to $6 per square foot.
In exchange for the expense, green roofs can last two to three times as long as a regular tar roof. “The life expectancy of waterproofing is increased to more than 40 years,” according to Chicago officials.
The price of a green roof doesn’t include the cost of any structural improvement to the rooftop. However, a cheaper green roof can weigh as little as 13 pounds per square foot when wet, so it’s quite possible that a basic green roof will need no extra reinforcement. On the other end of the spectrum, the most expensive green roofs pile as much as eight inches of soil and insulation on a rooftop, weighing up to 45 pounds per square foot when wet.
The most expensive green roofs can also require watering or even extensive gardening, though the least expensive need very little maintenance. “Some of them you mow, some of them you don’t touch,” said Matthew Carr, eastern regional manager for American Hydrotech, Inc., a green roof manufacturer.
Also if your project is close to the airport or noisy industries, a green roof can decrease the amount of outside noise that can be heard inside your project by as much as 40 decibels, according to DPD.
When McGough Development finishes its Reflections condominium project at Bloomington Central Station in Bloomington, Minn., in 2006, the green roofs on top of the buildings will help to keep out the noise of the Minneapolis-St. Paul International Airport nearby.
Green roofs can even help a project fight for the moral high ground in its struggle to win the approval of the surrounding community. Forest City Ratner Cos., based in Brooklyn, N.Y., is now considering placing green roofs on buildings at its controversial Atlantic Yards project, according to sources at American Hydrotech, Inc.
The massive mixed-use project would include 7,300 apartments. Forest City has reached out to the community in several ways, but still faces pockets of fierce local resistance.
Green roofs can also help keep buildings cool. The green roof on Chicago’s City Hall registered approximately 90 degrees on the hottest summer days last year while the roof on top of the Cook County Building next door registered 160 degrees Fahrenheit.
That lowered roof temperature can reduce the cost of cooling a single-story building by as much as 20% to 30%, according to DPD. However, these savings shrink rapidly in multistory buildings.