I have an 1865 2nd empire outside of Boston (zone 4) with no insulation, single glaze windows, 2 flat-ish roofs. I've been sealing all the gaps I can find, and now that the roofs are being replaced I can think about insulating.

But, I'm quite confused. I had an energy audit and the company really pushed having insulation blown into my walls for about $6000, and that was about all they said on the subject of weatherizing. Then I read that walls make little difference at all, and the gov't energystar seems to recommend R5 as just an afterthought for walls.

Meanwhile that website says R38-R60 for ceilings. I gutted one part and I think I have 6" rafters, no attic just a very small pocket under very shallow roofs. I think closed cell spray foam is my only option, but even there I have more questions... Do I need to pull down the other half of the ceiling to get the roof insulated? And what about the sides of the mansard roof, do they need to be spray foamed, and thus I need to rip out the top half of the walls? Or is blown cellulose okay there since it's sorta a wall and sorta a roof?

Then that gov't website recommended R25-30 for a floor...?!? Do they mean a ground floor, or a basement floor? I never even considered insulating the floor, should I? That would be easy, I think I have 12" joists. However, I have steam heat and the heater is in the basement with hot pipes everywhere, should I consider that a conditioned space or insulate all the pipes, too?

Any help would be greatly appreciated!