Designing a net zero energy building from the outset is easier than retrofitting an existing building, according to this article, but retrofits are indeed possible. It looks at four buildings that were retrofitted to become net zero energy. "Retrofitting existing buildings can be expensive, but the price is worth it to achieve sustainability," Kristen Avis writes. "New buildings can be strategically designed to achieve zero energy status without being extremely expensive. Both are a smart investment for the future of the planet."