rigid insulation for attic?
My house is a 1 1/2 story built in 1959. The upstairs is finished, with closets under the eaves/behind knee walls. There are no soffit vents but a few roof vents in the high part of the roof. The roof framing is 2x4. Asphalt shingles, about 5 years old. The insulation (at least what I can get to--behind the knee walls) is r-19 paper faced smooshed into the 2x4 space right below the roof deck with a layer of foil faced rigid insulation to the inside of that. This will be my first winter in the home (in Minnesota) and don't want to go broke on heating. What are my best options for keeping this house warm? From what I've studied, closed cell spray foam on the underside of the roof deck might be an option, but kind of expensive. Can I fill the spaces between the rafters with layers of rigid insulation instead, if I seal it? I'm hoping to keep as much of the ceiling height as possible, but I'm guessing I'll have to lose some. Other ideas?