![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Chicago's Heat Island Reduction Activities
Pilot Cities
- Denotes link to glossary
definition
Chicago has been a leading
city in launching heat island reduction measures. Some
highlights of the city's activities include the
following:
Landscape Ordinance
Energy Code
Rooftop Garden
City Hall Energy Savings
Other Benefits
Open Space Impact Fee Ordinance
Asphalt Alley Reconstruction
Parking Lot Resurfacing
Greening
Landscape Ordinance
Established in 1991 and updated in 1999, this ordinance covers three categories of landscaping: planting trees or shrubs on parkways; landscaping to screen the perimeters of parking lots, loading docks, and other vehicular use areas; and landscaping within these same parking lots, loading docks, and other vehicular use areas.
Parkway plantings are required in the construction of any principal building; any addition or enlargement to an existing building if the new construction exceeds 1,500 ft²; any repair or rehabilitation work of an existing principal building, including interior remodeling, if the expense of this work exceeds 50% of the structure's replacement cost; construction of any parking area containing five or more spaces; and repair or expansion of existing parking areas if the number of spaces is being increased by more than 25%.
Residences of three living units or less are exempt. Parking lots, loading docks, or other vehicular use areas smaller than 1,200 ft² are exempt from screening landscaping.
The Department of Zoning co-administers the Landscape Ordinance with the Department of Streets and Sanitation's Bureau of Forestry. As of summer, 2001, more than 2,000 new trees and 8,000 new shrubs had been planted due to this ordinance. Plans were approved for an additional 6,000 new trees and over 33,000 new shrubs.
Planting standards are maintained by the Bureau of Forestry, which also must inspect and approve all parkway plant materials prior to installation. All building and zoning permit applications are reviewed by the Chicago Department of Zoning to ensure compliance with the Landscape Ordinance.
For additional information, contact the Bureau of
Forestry at (312) 747-2021. Copies of the original
Landscape Ordinance are available to the public by
calling (312) 744-9044 or online at
Chicago's
Department of Environment
.
Energy Code
In January 2003, Chicago amended its energy code
requirements for reflective roofs. This code applies to
all buildings except: separated buildings that have a
peak design rate of energy use less than 3.4
British
thermal units
an hour per ft² or 1.0 watts per ft² of
floor area for all purposes; and unconditioned
buildings (i.e., those that are neither heated nor
cooled).
The amended code states that roofing materials used
in roofs with slopes of 2:12 inches or less must meet
the following requirements: for roofs installed on or
before December 31, 2008, a minimum
solar
reflectance
(both initial and weathered) of 0.25, when tested in
accordance with American Society for Testing and
Materials (ASTM) standards E 903 and E 1918, or by
testing with a portable reflectometer at near ambient
conditions; and for roofs installed after December 31,
2008, at least the minimum criteria to qualify for an
ENERGY STAR ® label as designated by the ENERGY
STAR ® program.
Rooftop Garden
Aerial view of Chicago's rooftop garden (courtesy of the City of Chicago).
Chicago began constructing its City Hall rooftop garden in April 2000 after 1.5 years of planning. In total, 20,000 herbaceous plants consisting of 156 varieties, 112 shrubs, and 37 vines were planted in a special blend of compost, mulch, and lightweight absorbent materials occupying 20,000 ft² of the 38,800 ft² roof. Rainwater is collected from 2,500 ft² of penthouse space and stored in holding tanks for periods without rain.
Close up view of Chicago's rooftop garden (courtesy of the City of Chicago).
The adjoining Cook County building, which has a
traditional black tar roof, provides good control data.
Weather stations have been set up on both halves to
monitor temperature, rainfall, and wind speed and
direction. City Hall's initial total roof
solar
reflectance
– or
albedo
– was approximately 0.27. The solar reflectance
of the total roof with the gardens and walkways is
0.45.
City Hall Energy Savings
Chicago expects the City Hall green roof to generate direct energy savings through a combination of shading, evapotranspiration – or evaporation of water from leaves – and insulation, which the rooftop garden provides as part of the green roof system. Rainfall in Chicago is the heaviest during the summer months, maximizing evapotranspiration effects.
Researchers used an energy model developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. to project cooling savings. The model indicated that evapotranspiration alone (not including the effects of changes in surface color, insulation, and shade levels) eliminates the roof cooling load. That is, the heat required to transpire the water from the garden is overwhelmingly greater than the roof cooling load. The fact that over 88% of the transpiration (413,808 gallons of water from an annual total of 470,754) occurs during Chicago's six-month cooling season greatly contributes to this effect. Further, part of the green roof system included adding a new layer of insulation, thus eliminating the typical heating season heating penalty.
Projected total direct electricity savings were
9,272 kilowatt-hours per year, and the corresponding
savings in natural gas for heating were 7.372 therms
per year. (This calculation compares the base case
R-value, or
thermal
resistance value
, of 5.9 with the treated roof – garden and
insulation – R-value 21.2.)
Other Benefits
The total available cooling effect from
evapotranspiration by the City Hall rooftop garden is
730% of what is needed to eliminate the cooling load of
the City Hall roof. The surplus cooling effect
available for the surrounding
microclimate
can reduce cooling costs in buildings downwind of City
Hall. Further, if green roofs were installed on all
Chicago roofs – approximately 30% of the city's
land is covered by building roofs – the avoided
peak energy demand would be 720 megawatts.
Reduced load on the storm sewer system would be 70%.
Air quality would improve due to removal of particulates, nitrogen dioxide, ozone from or by the vegetation, and reduced power plant emissions due to reduced energy consumption. Green roofs would also increase the amount of wildlife habitat for birds and butterflies.
Open Space Impact Fee Ordinance
The purpose and legislative intent of this ordinance is to require developers of new residential properties either to pay a fee or contribute a proportionate share of open space and recreational facilities, which directly and materially benefit the developments.
Open space impact fees are earmarked for open space acquisition and capital improvements, which provide a direct and material benefit to the new development from which the fees are collected. Fees may not be used to cure existing park deficiencies. Open space impact fees must be expended within the same or a contiguous community area from which they were collected after a legislative finding by the city council that the expenditure of fees will directly and materially benefit the developments from which the fees were collected. This ordinance was last updated in 1998.
Asphalt Alley Reconstruction
Making way for a porous pavement alley (courtesy of the City of Chicago).
Before reconstruction, this 10,080 ft² alley consisted of a three-inch asphalt overlay, ten inches of concrete, and no existing sewers. A gravel pave system was chosen for the reconstruction for its urban heat island benefits. The alley presented some construction challenges including an eight-foot elevation drop and 42 residential garage accesses. The new construction made the incline more gradual and created a footing on either side of the alley that matched or replaced the entry aprons of each garage.
Raking gravel into a Gravelpave2 system (courtesy of the City of Chicago).
The new gravel pave system was installed between the footings. This gravel pave system is light in color and reflects the summer sun. It also allows rainwater to filter into the subsurface, which is mainly sand, thus reducing the storm water load on the sewer system significantly.
Parking Lot Resurfacing
At the Institute for Cultural Affairs, a 2,300 ft² parking lot was converted from asphalt to a permeable brick paver surface with a solar reflectance of approximately 0.4. While this parking lot does have a sewer system, the permeability of the brick pavers helps to reduce the amount of storm water entering that system. The parking lot was also brought into compliance with the landscape ordinance, and the Institute has plans to exceed the ordinance requirements by adding trees and perennials around the parking lot perimeter.
Greening
Chicago also is a part of a series of greening projects involving replacing concrete and asphalt with green space and reflective surfaces throughout the city.
In addition to the above activities, Chicago has launched a series of neighborhood projects intended to demonstrate the applicability of urban heat island reduction techniques at the community level.
See the City of Chicago Department of the Environment for more information on Chicago's heat island reduction activities.