Just months after rolling out an ambitious plan to cut the city's carbon emissions by 25 percent over the next decade, Chicago officials took a long stride toward meeting that goal by adopting stricter building codes yesterday.

Considering that buildings -- and the energy it takes to heat, cool, and illuminate them -- make up for 70 percent of all of the city's greenhouse gas emissions, the new energy efficiency guidelines seem like a logical start.

To keep pace with the "Chicago Climate Action Plan," aldermen agreed to set the bar high. And the result was the adoption of even more stringent guidelines than those set out in the International Energy Conservation Code, a roadmap to building energy sustainability adopted statewide in 2006.

One of the toughest new rules is that any building taller than four stories will have to adhere to commercial building codes. To reduce the heat island effect, all low-slope roofs will have to equipped with a highly reflective materials that deflect at least 72 percent of all surface light. Not even historic or landmark building will be exempted from the rules, unless the integrity of the structure would be compromised.

The city anticipates that 421,000 new and rehabbed homes will be certified under the program by 2020. That will result in a reduction of 1.13 million metric tons of carbon emission, according to Larry Merritt, with the city's Department of Environment. The rules go into effect on April 22, 2009 (Earth Day).