Buried in a bill to cap carbon dioxide emissions are new standards meant to make homes and commercial buildings more energy efficient.

Residential and commercial buildings use 40 percent of the nation's energy and represent 40 percent of the carbon emissions in the United States, according to the Department of Energy. Buildings with leaky windows and out-of-date appliances use even more energy.

Curbing climate change by improving construction standards was something President Barack Obama talked about on the campaign trail; once in office, Obama said he would "establish a goal of making all new buildings carbon neutral, or produce zero emissions, by 2030," and that, in the meantime, he would establish "a national goal of improving new building efficiency by 50 percent and existing building efficiency by 25 percent over the next decade to help us meet the 2030 goal."

Looking at the fine print of the cap-and-trade bill recently passed by the House of Representatives, it seems the administration is on its way to fulfilling this campaign promise. According to a summary of the bill, new buildings will be 30 percent more efficient in 2012 and 50 percent more efficient in 2016. Those standards will increase five percent every three years. That means that by 2030, new buildings will be 75 percent more efficient than they are today — 25 percent below the efficiency standard Obama originally promised.

A sticking point: States will now be required to follow a national building code. Every three years, two organizations — the International Energy Conservation Code and the American Society of Heating, Refrigerating and Air-Conditioning Engineers — write new codes; states adopt them or they simply write their own. As a result, some states have very old standards — or none at all. The bill gives money to states to comply with the new rules, and if they don't, the Department of Energy can enforce them.

Existing homes are not subject to these new rules, though there are perks in the bill for homeowners who want to seal windows, upgrade appliances or do a major retrofit. The formula here is simple: the more energy an improvement saves, the more money a consumer can get from the government. Whether all these efforts add up to old homes that are 25 more energy efficient is unclear.

The cap-and-trade bill includes rules that will improve new building energy use by 75 percent in 2030, which is 25 less than Obama had originally promised. It also includes new programs to encourage upgrades to existing homes and commercial buildings, but it is unclear whether those perks will improve efficiency by 25 percent. The bill is still slated for debate in the Senate, where any number of changes could be made. Until the bill is enacted, we rate this one In the Works.