Vegetated Roofs

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).

Plant Specifications

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.