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Vegetated Roofs

FedEx Main Sort Building vegetated roof installation, June 2011

The Sustainable Airport Manual (SAM) developed by the Chicago Department of Aviation (CDA) established contractual requirements to incorporate sustainability in the design and construction of every project at O'Hare and Midway International Airports. The SAM encourages the installation of vegetated roofs on airport facilities wherever possible to reduce the urban heat island effect, conserve energy, and reduce storm water runoff.

Installing vegetated roofs atop airport facilities has proven to be an effective method for counteracting the heat island effect

As shown in the table below, the CDA has installed 338,171 square feet (ft2) of vegetated green roofs at O'Hare on 12 different facilities including a guard post canopy, a lighting control system facility, parking/rental car facilities, and the first vegetated roof ever installed on an airport traffic control tower administration facility. The CDA has also installed vegetated roofs at Midway on the Economy Elevated Parking Structure and Electrical Vault and on top of the Midway Consolidated Rental Car Facility.

Vegetated Green Roofs at O'Hare International Airport Size (ft2)
Aircraft Rescue and Fire Fighting Facility #3 3,440
Guard Post #1 Canopy 6,500
South Airfield Lighting Control Vault 14,200
North Airport Traffic Control Tower Base Building 8,910
North Airport Traffic Control Tower Electrical Building 917
FedEx Vehicle Maintenance Building 3,170
FedEx World Services Center 10,024
FedEx Main Sort Building 174,442
Enterprise Rental Car Maintenance Building 3,627
Enterprise Rental Car Customer Service Center 2,847
Booster Pump Station (Building 815) 1,278
United Airlines Cargo Building 108,816
TOTAL 338,171

Vegetated Roof Benefits

The CDA has taken a "lead-by-example" approach, installing vegetated roofs atop airport-owned facilities and encouraging tenants to follow suit. The CDA's installations demonstrate that installing vegetated roofs at airports is practical and cost effective. Operational and maintenance cost savings are expected from increased roof life span, energy use reduction, and storm water quantity/quality management. Additional benefits achieved include a reduction in noise and heat islands, air quality protection, and enhanced aesthetics.

Water Management/Stormwater Management

Vegetated roofs increase storm water retention, filtration, and evaporation in a predominantly impervious urban area. It is estimated that vegetated roofs at the CDA's airports can retain 70-90 percent of the precipitation that falls on them during the summer and 25-40 percent in the winter. For example, the FedEx Main Sort Building vegetated roof is estimated to retain approximately two million gallons of storm water annually. In conjunction with the other vegetated roof space at O'Hare, the vegetated roofs may decrease the need to expand or rebuild costly drainage infrastructure.

Roof Longevity

By protecting the roofing membrane from exposure to ultraviolet rays, temperature extremes, and precipitation, a vegetated roof can prolong the roof lifespan from 15-20 years to 40-50 years. Although a conventional PVC roof has a lower installation cost, it can cost around $9.00 per square foot for tear off and re-roofing every 15-20 years. At this rate, for example, the 174,442 square-foot FedEx Main Sort Building vegetated roof's increased longevity could save the CDA approximately $1.5 million in avoided re-roofing costs by doubling the roof's life span.

Reduction of Energy Costs

Vegetated roofs improve thermal insulation and counteract the heat island effect, helping the airport reduce heating and cooling costs. The heat island effect causes overheating of cities during the summer, leading to excessive energy consumption for air conditioning and pollution from electric power generation. Energy savings are estimated at around $0.20 a square foot per year. At this rate, the FedEx Main Sort Building vegetated roof saves the CDA approximately $35,000 per year in energy costs or $1.4 million if assuming a 40-year life cycle.

Acoustic Buffering

Sound waves produced by construction equipment, vehicle traffic, and/or airplanes are absorbed or deflected by the soil, plants, and the trapped layer of air on a vegetated roof. It is estimated that a four-inch vegetated roof substrate layer can reduce the level of sound penetrating inside the building by around 40 decibels.

Reduce Air Emission Impacts

Roof foliage absorbs dust and greenhouse gases and filters airborne particles. It is estimated that one square meter of vegetated roof can remove about four pounds of airborne particulate matter per year.

Educational Value

Millions of visitors observe O'Hare's vegetated roofs while traveling on the Airport Transit System, driving to the airport along Mount Prospect Road, or when flying overhead, making the CDA's commitment to the environment very visible. O'Hare, the second busiest airport in the U.S., was visited by nearly 67 million passengers in 2012. The sedum plant species used by the CDA have white or yellow flowers and green, light green, or maroon foliage that catch the eye of passing visitors yet are tolerant to drought and do not attract wildlife. The vegetated roof installations also support a broader City-wide interest in green roofs –  Chicago is the green roof capital of the U.S.

Airport-Specific Vegetated Roof Considerations

There are some unique elements and regulatory factors in an airport environment that present challenges to expand vegetated roof space, including wildlife attractants, protection of mission critical equipment, height limitations during construction, secure access restrictions, and prevention of foreign object debris (FOD).

Native, low-growing sedum species planted on the North Airport Traffic Control Tower Base Building vegetated roof to reduce attractiveness to wildlife

The CDA's vegetated roof plantings must be a species that is unattractive to wildlife to minimize the potential for aircraft bird strikes. Sedum species such as white, tasteless, dragon's blood, orange, and goldmoss stonecrop were chosen for their lack of food production, such as berries or seeds, and deficiency of habitat, thereby reducing their attractiveness to wildlife. All the species are perennials naturalized to North America and can be found as ground cover in many states.

Sedum Species Common Name Flower Height (cm)
album White Stonecrop White 5-10
sexangulare Tasteless Stonecrop Yellow 5-10
spurium Dragon's Blood Stonecrop Pink 10-15
stenopetalum Wormleaf Stonecrop Yellow 5-10
ellacombianum Orange Stonecrop Yellow 10-15
pulchellum Widow's Cross Pink 10-15
oreganum Oregon Stonecrop Yellow 5-10
hybridum Czar's Gold Yellow 10-15
relfexum Blue Spruce Yellow 10-15
acre Goldmoss Stonecrop Yellow 5-10

Damage to aircraft from FOD can be very costly. Therefore, the CDA and its tenants have ​designed green roofs in compliance with wind speed requirements to prevent parts of the plants or bedding from blowing off the roof and onto aircraft movement areas.

O'Hare Vegetated Green Roof Inventory

Aircraft Rescue and Fire Fighting (ARFF) Facility #3

Aircraft Rescue and Firefighting Facility #3 vegetated roof

A 3,440 square-foot vegetated roof was installed on ARFF Facility #3 in 2006 to help improve air quality, conserve energy, reduce storm water runoff, reduce the urban heat island effect, and serve as an insulated roof and a radiant barrier. The installation of the tray-based system marked the first vegetated roof installed by the CDA. The planting, which includes sedum and other groundcover, is visible by Airport Transit System riders who can see the roof as they travel to and from the terminal and remote parking lots. The vegetated roof on the firehouse also features 10 solar thermal collectors that capture the sun's energy; this energy is used to heat water that is circulated in metal tubes to provide hot water for the firefighters who work in the building.

Mount Prospect Road Guard Post #1 Canopy

Mount Prospect Road Guard Post #1 Canopy vegetated roof

The Guard Post #1 Canopy, completed in 2007, is covered by a 6,500 square-foot vegetated roof. The roof design reduces the urban heat island effect, reduces the peak flow rate of storm water, and allows for the retention of storm water runoff that would otherwise flow to the storm water system. The vegetated roof on the guard post is a visible display of the City of Chicago's commitment to the environment at the northwest airport entrance.

South Airfield Lighting Control Vault (SALCV) and Duct Bank Building

South Airfield Lighting Control Vault and Duct Bank Building vegetated roof

Completed in 2008, the 14,200square-foot vegetated roof installed on the SALCV and Duct Bank Building consists of an extensive system with six inches of growing medium. The SALCV provides and regulates electrical power for runway and taxiway lighting. Workers monitoring the facility have reported cooler temperatures inside the building during summer months compared to conventional facilities of the same size. The protected membrane roof and waterproofing assembly consists of a rubberized asphalt membrane, polyester reinforcement, drainage/retention mat, root barrier, and extruded insulation.

North Airport Traffic Control Tower (NATCT)

North Airport Traffic Control Tower Electrical Building vegetated roof

The Federal Aviation Administration (FAA) NATCT, which opened in November 2008 to accommodate Runway 9L-27R, features nearly 10,000 square feet of vegetated roof space on top of the base (8,910 square feet) and electrical (917 square feet) buildings, making it the first on-airport FAA facility in the nation to feature a vegetated roof. Critical airport traffic control equipment is housed underneath the vegetated roof in the administration and electrical buildings. The installations demonstrate the CDA's confidence in vegetated roof technology and willingness to consider vegetated roofs on all airport facilities.

The vegetated roofs and energy efficient electrical devices decrease energy use by approximately 35 percent compared to baseline consumption levels. As a result of the sustainable initiatives incorporated into the project, the tower earned a four Green Airplane Certification based on the SDM rating system and is the first tower in the nation to earn United States Green Building Council (USGBC) LEED® Silver certification.

Booster Pump Station

Booster Pump Station vegetated roof

In 2010, a pump station was constructed southeast of the Aviation Administration Building along Bessie Coleman Drive. As part of the construction, a 1,278 square-foot vegetated roof system was installed that covers about 75 percent of the building's total area (approximately 1,716 square feet).

Federal Express (FedEx) Sort Building, World Services Center, and Vehicle Maintenance Building

FedEx Sort Building vegetated roof

The construction of Runway 10C-28C as part of the OMP required the relocation of the FedEx Metroplex and  other existing facilities in 2010. As part of the relocation, a 174,442 square-foot vegetated roof was installed on the relocated FedEx Cargo Sort Building, the largest vegetated roof at any airport in the U.S. and the largest vegetated roof on a free standing building in the greater Chicago area (three football fields). The Sort Building vegetated roof is located within 200 yards of an active runway in an area subject to height restrictions and is surrounded by active airspace on three sides.

FedEx Vehicle Maintenance Building Vegetated Roof

The roofing system needed to be wind resistant and leak proof, fall under a unified warranty (covering water tightness, success of plants, and overburden removal and replacement), and allow for easy identification and quick repair so that FedEx operations would never be compromised. The installation included 3.9 acres of pre-vegetated mat, more than 2,200 cubic yards of media and 3 miles of edging. It is estimated to have a saturated weight of over 4 million pounds and retain about 2 million gallons of storm water annually. In addition, a 3,170 square-foot vegetated roof was installed on the FedEx Vehicle Maintenance Building and a 10,024-square foot vegetated roof was installed on the World Services Center.

Enterprise Rental Car Maintenance Building & Customer Service Center

 Vegetated roofs are located on the Enterprise Rental Car Maintenance Building and Customer Service Center

The Enterprise Rental Car facility at O'Hare opened in the summer of 2010 and features vegetated roofs on the maintenance building (3,627 square feet) and the Customer Service Center (2,847 square feet). The Enterprise facility incorporates several sustainable initiatives such as high efficiency fixtures to reduce water consumption and the use of recycled construction materials. The facility also obtained U.S. Green Building Council LEED® Silver certification.

United Airlines Cargo Building

The CDA installed a 108,816 square-foot vegetated roof on top of the relocated United Airlines cargo building in 2011. The installation is the CDA's newest at O'Hare and second largest vegetated roof to be installed.