I live in a 2 story city row house in Philadelphia that is over 100 years old with a flat roof. The space between the second floor ceiling and roof grades down from the front to back - 36 inches or so to 0 when they meets in the rear. The top floor has 3 bedrooms and a bathroom. I already did the front and middle bedrooms, however I did not do any insulating in the ceiling space for those two rooms and regret it now and I am not willing to tear down the finished ceilings.
So now that I am doing the third bedroom, I want to insulate. My first thought is to pull down the lathe and plaster ceiling, put a few inches of rigid foam board between the rafters, some faced fiberglass batts between the ceiling joists(they are not always 16 OC * advise please) and the put the drywall ceiling up. Is it worth all the effort since the 2 other ceilings are not insulated at all?
I know there is the blow in loose stuff, but not sure someone can fit in in that space. I heard that some people have contractors cut holes in the roof and shoot it in from the top, but is that inviting issues?
If the cutting in the flat roof isn't a big deal should I have it done to the entire roof? Can it be the closed cell foam to make it all air tight?
Or should I carry on and come back to the other two ceilings later, most likely blow in from above. Is it ok to have 2 different insulation schemas under the same roof?
I know I am being indecisive but I want to do the right thing now that I have the chance.