Chicago is already home to the highest number of green rooftops of any city in the world, including Chicago’s City Hall’s Rooftop Garden. The next initiative being undertaken by the city is the Green Alley Program. This project is an expanded approach to Chicago Department of Transportation’s existing alley program and is designed to improve those alleyways in a sustainable way. The city contains one of the most extensive networks of alleyways in the world, covering 1,900 miles with over 3,500 acres of paved, impermeable surfaces. A number of improvements have been suggested for the Green Alley Program including the use of permeable surfaces, high albedo pavements, and recycled material.

1) Permeable Pavement- Permeable pavement has pores or openings that allow water to pass through the surface and percolate through the existing subsoil. Permeable pavement comes in the form of permeable asphalt, permeable concrete, and permeable pavers. In areas where soils do not drain freely, permeable pavement can be used in combination with subsurface drainage systems, like pipe underdrains or stormwater infiltration trenches to slow runoff and reduce stress on the combined sewer system.

Potential Benefits

• Reduces the rate and quantity of stormwater runoff

• Reduces stress on the sewer system

• Recharges ground water

• Filters silt, pollutants and debris

2) High Albedo Pavement- High albedo pavement material is light in color and reflects sunlight away from the surface. With less sunlight absorbed by pavement, less heat is radiated by the pavement. High albedo pavement therefore reduces the urban heat island effect. This reduces cooling costs, helps the survival of urban vegetation, and improves air quality, which can help reduce the symptoms of some respiratory diseases.

Potential Benefits

• Reduces the urban heat island effect

• Can be used under a wide variety of site conditions

• Conserves energy by reducing cooling costs

• Improves air quality

3) Recycled Construction Materials- Recycled construction materials can be incorporated in a variety of ways in green alleys. Recycled concrete aggregate can be used in the concrete mix and as a base beneath surface paving. Also, slag, a by-product of steel production, can be used as a component of the concrete mix, reducing industrial waste. Ground tire rubber can be used in porous asphalt and reclaimed asphalt pavement in non-porous asphalt.

Potential Benefits

• Reduces waste hauled to landfills

• Reduces the need to extract virgin natural resources

Brief History of Millennium Park:

You might never guess that Millennium Park, recipient of the 2009 Rudy Bruner Award for Urban Excellence, was once an industrial wasteland transformed into a world-class public park. In fact, from the 1850s until 1997, the land that is now occupied by Millennium Park was controlled by the Illinois CentralRailroad. Visionary Chicago leader Daniel Burnham considered the railroad’s control of this area, covered with unsightly railroad tracks and parking lots, to be so untouchable that it remained blight on Chicago’s lakefront throughout the 20th century.

What is now Millennium Park was first conceived in late 1997 with Mayor Richard M. Daley’s vision of turning the area into a new public space for residents of Chicago. Over time, with the commitment of the private sector and the involvement of world-renowned architect Frank Gehry, the project evolved into an ambitious undertaking featuring a collection of world-renowned artists, architects, planners, landscape architects and designers. Today, the 24.5-acre Millennium Park represents an unprecedented public-private partnership, and has become a thoroughly modern achievement for Chicago in the tradition of its original founders.

The Lurie Garden:

Designed by Gustafson Guthrie Nichols Ltd., Piet Oudolf and Robert Israel, this 5 acre garden pays homage to the City's motto, "Urbs in Horto" (City in a Garden), which refers to Chicago's transformation from its flat and marshy origins to a bold and powerful city. Highlights of The Lurie Garden include the dramatically lit, 15-foot-high "shoulder" hedge. This physical representation of Sandburg's famous description of the "City of Big Shoulders" encloses the garden on two sides and protects the delicate perennial garden from the throngs of concert-goers to and from the bandshell. This structure exemplifies the unusual strength and structure of this Chicago garden, where plants rise taller than people.

Garden Components:

The Extrusion Plaza- The Extrusion Plaza is an extension of the existing north-south circulation spine through Millennium Park. It links Monroe Street and the southwest Exelon Pavilion with The Lurie Garden and continues north toward the Pritzker Pavilion and the rest of Millennium Park.

The Shoulder Hedge- A giant, muscular hedge encloses the interior Garden from the north and west. From the Art Institute, the "big shoulders" of the Shoulder Hedge appear to support the gleaming "headdress" of the Pritzker Pavilion to the north. The Hedge is a living wall that protects the delicate perennials within the Garden from heavy pedestrian traffic moving throughout Millennium Park.

West Hedge- The West Hedge is a topiary feature that playfully tells the classical Greek story of a nymph who escaped from Apollo by becoming a Laurel tree. In contrast to the historical references within the Garden, this story explores the futuristic theme of the Garden that is expressed in the Light Plate - Chicago's powerful control of the natural landscape for urban growth, industry, and agriculture.

Dark Plate- Strong, nostalgic, mysterious and cool, the Dark Plate expresses the early landscape history of the site and the city. The site was once a wild shoreline and river delta. The challenging character and lush feeling of this historic condition is in dramatic contrast to the current elevation and form of Millennium Park.

Light Plate- The Light Plate renders the future in an exhilarating landscape. The Light Plate is bold, warm, dry and bright. Unlike the volume of the Dark Plate, in which a person feels enveloped, the Light Plate is a contoured, controlled plane experienced by walking on its surface.

Seam- The Seam is the special corridor or "break" between the two Plates. It is not a thoroughfare, but rather a place to casually stroll.

Boardwalk and Water Features- The Boardwalk floats over stepped pools, leaving a 5' wide exposed surface of water along the Dark Plate's vertical stone face (the Seam Wall). The Boardwalk is built of sturdy Ipe wood and is designed as a strolling path as well as a place to gather.

Lighting- At night, The Lurie Garden transforms into a subtly glowing "container" of light. The Shoulder Hedge acts as the solid container to this soft and magical night scene. This focuses anticipation and attention on those special openings and pathways that break the form of the Hedge and allow the inviting, interior light to be seen.

Chicago’s City Hall rooftop has varying sections containing soil depths of 4, 6, or 18 inches to accommodate the different plants and trees. Soils were developed from lightweight mixtures similar to those used in Germany over the last few decades. Under the soil is a 12 to 24 inch waterproofing layer that provides structural support for weights of up to 60 pounds per square inch. The rooftop is home to over 20,000 herbaceous, 100 woody shrubs, 40 vines, a Cockspur Hawthorn tree, and Prairie Crabapple tree. The plants and trees are organized to bloom in a sunburst pattern.

75% of each inch of rainwater is collected and used before runoff begins to occur. Even more impressive is the fact that the rooftop is that the air temperature is reduced by 15 degrees with the actual rooftop temperature being 70 degrees cooler than comparable, adjacent roofs. The garden rooftop also contributes $5,000 in annual energy savings. Initial data results have been highly encouraging and the Chicago City Hall Rooftop Garden is serving as a model for other buildings with green rooftops, both in and outside of Chicago.

While the garden is not normally accessible to the public, Chicago Gateway Green has exclusive footage below of Bill Kurtis interviewing Mayor Daley atop the City Hall.