The house in Boulder, Colo., was beautiful. The floors were cork, the carpets were made of recycled plastic bottles — the whole place was being redone on sustainable, environmental principles. “It was mind-expanding,” says Jason Ballard, the co-founder and CEO of eco-friendly home improvement retailer TreeHouse. The house belonged to Ballard’s instructor in a wilderness EMT program. Ballard was staying there shortly after college, and he was inspired by his instructor’s efforts to remodel his home to make it more environmentally friendly. “It was such a lovely vision of what was possible,” he says.