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.
The CDA has installed 20,819 square feet of vegetated green roofs at Midway on four different buildings.
The CDA has also installed 338,171 square feet of vegetated 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.
Midway Consolidated Rental Car Facility
In April 2013, the CDA opened a facility at Midway that consolidates rental car customer service centers, facilities and parking lots into one convenient location reducing congestion, vehicle emissions and shortening wait times for car renters.
The consolidated car rental facility includes a 17,640 square-foot vegetated green roof as well as green walls, solar panels and rainwater collection cisterns for drip irrigation and car washing.
Economy Elevated Parking Structure and Electrical Vault
A total of 3,179 square feet of vegetated roofs were installed on two entrance vestibules to the Midway economy elevated parking structure and the 1,400 square-foot electrical vault building in June 2008 (4799 West 54th Street).
The vegetated roofs at Midway and O'Hare require careful consideration to
certain elements and regulatory factors that are unique to an airport
environment including wildlife attractants, protection of mission
critical equipment, height limitations during construction, secure
access restrictions and prevention of foreign object debris (FOD).
The 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 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.
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.
The Benefits of Vegetated Roofs
The CDA's green roofs 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.
1. 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 vegetated roof at the FedEx
Main Sort Building 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.
2. 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.
3. 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 per square foot each year. At this rate, the FedEx Main
Sort Building vegetated roof saves the CDA approximately $35,000 annually in energy costs or $1.4 million if assuming a 40-year life cycle.
4. 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.
5. Reduced Air Emission Impact
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.
6. 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.