An all-season "smart roof" coating keeps homes warm during the winter and cool during the summer, without using natural gas or electricity, a study published Thursday in the journal Science found. The technology, called temperature-adaptive radiative coating, outperformed currently available commercial cool-roof systems in energy savings in cities representing 15 different climate zones across the continental United States, the researchers said. With temperature-adaptive radiative coating installed, the average household in the United States could save up to 10 percent of electricity consumption annually, researchers said."Our all-season roof coating automatically switches from keeping you cool to warm, depending on outdoor air temperature," study co-author Junqiao Wu said. "This is energy-free, emission-free air conditioning and heating, all in one device, said Wu, a professor of materials science and engineering at the University of California, Berkeley.