In 2013, San Francisco got its first passive home (Seattle built one the year before). This year, we predict the high-efficiency building method will gather steam. Not sure what a passive home is? It's built similarly to a typical home except it's 100 percent airtight. Instead of a furnace, the house has a heat recovery ventilator machine that pulls hot hair out of kitchens and bathrooms, draws in fresh air from outdoors, then uses the hot air to heat the fresh air and pushes it into the living spaces. The best part—the homes work in any climate, not just temperate ones.