When Ryan Shanahan, 41, decided to buy a house in Portland, Oregon, he knew from the start that he wanted his future home to be "net zero." To be net zero is to cut greenhouse gas emissions to as close to zero as possible, with any remaining emissions reabsorbed from the atmosphere, by oceans and forests, for instance, according to the United Nations. "My mantra is that the future is efficient, electric, and renewable," Shanahan tells CNBC Make It. To buy the house, Shanahan took advantage of a $15,000 forgivable loan from Oregon's Down Payment Assistance program. Shanahan purchased the house because it had design features needed to help reach his goal of making the house net zero.

---