we are in the process of tearing out our stairs to move them, and rebuilding a room under our main living room. Given that the top part of the room was built in 1975, and the lower part was built in 1948 (or before) we were pretty sure that we had a lot of opportunity to make some changes in how things were insulated. Our access to the attic was outside the house, so we had a lot of big holes where that was. There was only 3" of steel wool insulation in SOME of the attic, so when I moved it over and tore down the ceilings, we were able to see where the issues were. I went around and foamed and caulked all of the holes going into the house. There are no soffit vents, but I added some rafter ventilators where I could get to the open rafters. In some spots, there were holes the size of baseballs where the cold air was rushing in.
I of course made sure to do it on the day that it was -9ºF, so it was really apparent (that is also the only day I had a fire in the house this year, because the house was 24º inside and one of my water pipes broke). We have been slowly adding insulation and caulking where we can. We have replaced most of the windows, and there is only 1 left that is the original single pane window. I keep trying to replace it but my wife likes the look of it. While I was poking around and having to move a water line, I discovered that above my hallway, they had put a single piece of insulation to make it look like there was some there, but it was all open air space. That of course leads all the way into our living room, as well as our bedrooms, so no wonder it was super cold! That is getting fixed next week when I blow in insulation.
The other thing that I ended up doing was filling the cinder block with insulation in the basement. Since we had everything ripped out to the joists, I was able to fill the blocks with loose fill insulation, then cap it off with some batt insulation. I make sure to foam and caulk all the way around the sills and top plates. We then firred out the walls with 2x4, and I used R13 on the exterior walls. I made sure to fill all of the gaps and cracks between the joists and beams with either foam or insulation. Since the bedroom is underneath the main entrance, I put in some rockwool insulation for sound and fireproofing. I made sure to insulate my time capsule well too
In the main living room, we opted to go with a vaulted ceiling, made of 2x6, that I filled with R21 all the way up and across. Even though most of the walls are 2x4 in this space and I didn't take anything out, I ended up putting R21 in the previously uninsulated wall. I made sure to seal up all of the corners, gaps, and cracks.
We are going to blow insulation back on the other section of the house, so we are hoping that will make things much warmer!