I have a 1715 Cape with old windows. The windows have been dated to the early 1800's. Still have old glass in them. Considering the cost of fuel oil nowadays, I want to tighten up the house. I'm curious about the thermal efficiency of putting new windows in (12 over 12) vs. reglazing the old windows and installing new storms (invisible). Also should say that I would like to put new siding on the front. Presently, there is the original Oak/chestnut sheathing with the original shakes and a layer of cedar shingles over the shakes. I do not believe there is any insulation in the wall as the interior plaster appears to be applied directly to the inside of the exterior sheathing. Any insulating ideas for the wall would also be appreciated.