Insulation, Radiant and Vapor Barriers - to insulate or not to insulate!

The house is Turn of the Century Victorian in Massachusetts. Winters are cold. The house appears to be uninsulated all around. We will be installing new, energy efficient windows throughout. The house has aluminum siding. Here's the question: along with the new windows, would it be enough to insulate the attic floor only? (heat rises) or should all the walls of the house be done as well? Thanks!

Length times width gives you the surface area. If you calculate the area for your attic let's say 30 feet by 30 feet equals 900 square feet. If you do the same for your walls 30 feet wide and 20 feet tall equals 600 square feet, but you have four walls equals 2400 square feet (600 x 4). To be fair you should subtract the windows and doors from the wall area. So let's say you have 20 windows at 15 square feet each (20 x 15 = 300 sq. ft.) and 4 doors at 20 square feet each (20 x 4 = 80 sq. ft.) So your net wall area is 2400 - 300 - 80 = 2020 square feet. Which by the way is more than double the surface area of your attic.

When calculating heat loss for a home, one of the major factors is surface area that separates the outside from the inside. Considering the usual configuration of your type of home, it is more cost effective to insulate your walls than your attic, based on surface area alone.

Aluminum siding mean that in order to insulate the walls will require drilling holes through the plaster from the inside. If you are a handy DIY'er, then fixing the plaster and repainting the walls won't be too bad expense wise, but will be time-consuming.

Another consideration is old knob-and-tube wiring. These houses commonly had this stuff, and some if it may even still be working. It is a big no-no to insulate joist or stud cavities that have knob-and-tube wiring due to it potentially being a fire hazard.

Thanks for the insights, in particular about the knob and tube wiring. We are having much of it, but possibly not all of it, removed. We'll need to know where the remainder will be and avoid insulating those areas. Can that be done? Can my electrician tell me where any remaining knob and tube wiring would be?

Can my electrician tell me where any remaining knob and tube wiring would be?

Generally, yes. There may always be some that remains undetected. It would be a good idea to remove all of it, so you don't have to deal with in the future. (If money were no object.)

Hope this helps.