With 2 new solar homes currently under construction, I have also been doing quite a bit of retrofit. In Inverness California, we installed Ray-Core R-36 double foil face polyurethane structural panels over a non-insulated gable roof. In Bozeman Montana we recently added 4" of Sub-grade Rigid Foam, an underground tempered air system, and a foundation drainage system to arrest mold development and substantially improve thermal efficiency. In Columbia Missouri, I designed and supervised the construction of a 5,000sf passive and active solar home, the first grid tie connected house in all of Boone County. In my own home, we retrofitted our 1958 forced air furnace into a "radiant" forced air furnace, and shaved a 1/3 off the energy bill.