I should have been more specific: 90% of my fossil fuel expenses are for heat, namely fuel oil and propane. The remainder of those expenses are for gasoline —farm tractor, mowers, automobiles, etc.
As to insulation: wrapped the house in Tyvek when I re-sided it, but doing more is not possible because this is a 232-year old historic property and I’m not going to destroy what has survived that long in such original form. I’ve done a lot to get rid of “death-by-a-thousand cuts” leaks, and have compromised on storm windows (not historically correct), and the old girl isn’t drafty anymore. But that’s about it — blown in insulation tends to attract mold, and I don’t know of any good alternatives. My in-laws had foam blown in, but had to sell because they became allergic to the off-gases from that process, so I’m not going there!
So, what do they do for castles and such in Europe to meet minimum insulation requirements?