The overarching goal is an 80 percent reduction below the city's 1990 greenhouse gas emissions level by 2050, with an interim goal of a 25 percent reduction by 2020. The difference between the city's 2005 trajectory and its 2020 goal is 15.1 million metric tons of carbon dioxide equivalents (MMTCO₂e). To give a sense of what that figure means-it's about equal to removing 2.8 million cars from the road.

To achieve this goal, the plan sets out five strategies. Energy-efficient buildings are number one. Chicago residential housing units number just over a million, at least 80 percent of which are expected to be standing in 2020. The aim is to achieve 30 percent energy savings in 40 percent of the city's residential housing stock. Commercial, institutional, and industrial buildings in Chicago number upwards of 23,000. Again, the 2020 aim is a 30 percent energy reduction in 40 percent-or 9,200-of them. Combined with other strategies, targeted savings in the building sector account for 4.6 MMTCO₂e or 30 percent of the 2020 total.

At the residential scale, building heat loss is the most significant energy drain. Heat loss occurs either through direct loss, as air moves through gaps in the building envelope, or through temperature differential, as components of the building envelope conduct heat out. Air sealing addresses direct heat loss and insulation addresses heat loss through temperature differential. "Those are the two main things we do," says Tom McElherne of DNR Windows, an established Chicago area weatherization contractor. DNR performs a blower door test of a building's air leakage before and after each weatherization project. "If you don't cut that number," says McElherne, "you're not going to cut their bills." Faith Foley, assistant director of the Historic Chicago Bungalow Association, agrees: "Air sealing is so crucial in any household, more than insulation even-that's where we're educating."

The Chicago bungalow, a brick masonry housing type built between 1910 and 1940, accounts for more than a third of Chicago's single-family housing stock. The bungalows' commonalities and the organization of their owners into an association makes the bungalows an ideal testing ground for a new program under development with the Center for Neighborhood Technology (CNT) in cooperation with Community Investment Corporation.

Based on a database of actual energy use for the 1.2 million single-family homes in Cook County, CNT Energy is developing a website where home owners can find out their home's energy score and rank it against comparable homes. The Web site will make retrofit recommendations tailored to the specific home, and provide connections to qualified contractors to do the work. Further supporting the value of retrofits, the database will ultimately enable the retrofits to measure in the real estate market. With an average project cost of $8,600, early results coming in from the bungalow retrofit program suggest 60 percent of bungalows are showing a reduction in utility bills of more than 25 percent.

Another CNT program, Energy Savers, serves owners of multi-family rental buildings. Steve Thomas of Genesis Group, an owner of several low-income rental properties, is retrofitting three buildings with Energy Savers. "It's been very enlightening, very helpful," he says of the energy audit CNT conducted on each building, and the report they provided identifying the buildings' inefficiencies, making recommendations for retrofitting, and quantifying savings and payback periods.