Glad to see some comprehensive writing about net zero. I truly believe that all new homes should target net zero. But, if all new homes are net zero, but we ignore existing homes, then we will not reduce our total carbon output. We need more discussion about converting the existing housing stock. We have proved what's possible. For a retail cost of under $50,000 we turned our 110-year-old Victorian home (in a historic district) in America's oldest and Michigan's first net-zero energy home. We have 4 years of consumption data and by October we will have a full year of solar production data. Have a look at two of the many articles written about the house. This is not a gut rehab. It is what is possible in many existing homes. http://www.hourdetroit.com/Hour-Detroit/March-2011/The-Nation-039s-Oldes... http://www.solartoday-digital.org/solartoday/201103#pg22