I have a home in Zone 5, built in 1971 and it is very under insulated. Walls are standard 2×4 however, it is vertical wood cedar plank siding right on the sheeting. There is no vapor barrier or tar paper.  Insulation is old deteriorating R13 in the walls.

The roof is a flat roof, combo of shingles on the cathedral and TPO on the flats. Joists are 2×8 however only R-13 in those bays as well. The roof was replaced in 2019 and under the TPO I do have 2” of EPS or Polyiso, I’m unsure which one. 

Obviously I need to add insulation and wanted some advice.

For the roof I am thinking flash and batt, 3” closed cell and rockwool R21 to fill the cavity. That should get me R42 not accounting for the eps under the TPO. 

For the walls, Im going to air seal with canned foam and caulk and use rockwool R15. However, that still leaves me with the issue of the siding. If I do the siding, Id replace with a wood look vertical cement siding. Should I also add on 2” of continuous insulation on the outside as well? 

My overall goal is to reduce my utility bills and increase my overall comfort with less drafts and cold spots.