Geoff and Joanna Mouming’s compact modern farmhouse is the first permanent structure at Yum Yum Farm in Wellman, Iowa. On the field that stretches out before it, organic vegetables will soon make attentive farmers of the Moumings. Photo by: Mark Mahaney  Photo 1 of 9 in The Eco-Friendly Guide to Upgrading an Existing Home from Modern Homes Across the American Midwest