Energy-efficient construction will need to adopt radically different design principles if it's to make the most of its potential, says high-performance-building expert Guido Wimmers. There are plenty of ways to make buildings more efficient, Wimmers says, but the simplest would be to stop using huge sheets of glass instead of more insulating materials. "Huge curtain walls are not God given," he argues. "Nobody is forcing us to design them. We don't have to build another glass box -- another aquarium."