Since the energy crises of the 1970s, the United States has known it has an energy problem. Yet today, the energy requirements in building codes remain weak across half the country, and at least seven states have virtually no rules. That means that in many places, particularly the nation’s heartland, almost every new home, store and factory that goes up locks the country into unnecessary energy use for years to come.

The problem is not just construction defects like the one Mr. Umphress caught, though those are plentiful. In many places, builders are still using too little insulation. Citing cost, they have not adopted the most energy-saving water heaters, roofing materials or window panes.

The Energy Department reports that buildings and the appliances inside them account for almost 40 percent of the carbon dioxide emitted in the country.

Stricter codes have been fought bitterly by politically powerful builders’ lobbies, which contend that they can add $2,000 or more to the cost of a house. But in a few places, including cities like Austin and entire states like California, tough new rules have been adopted.

The efforts of these localities show that no new technology needs to be invented to make major gains in saving energy. Products already available permit the construction of homes at least 30 percent more efficient than the national average. With enough political will, a new law can be put in place anywhere with the stroke of a pen, and made even more potent if it is coupled with tough oversight, as in Austin.