Hello house enthusiasts,

I’m hoping for some confirmation/correction/advice in plain English regarding improving insulation on my existing home.

The details:
Northern NM, built 1986, <1,700sqft, single story, stucco exterior, 2×12 roof joists spaced at 24” with R30 fiberglass batts and a total of 9 vents (pictured) on the north and east walls, walls are 2×6 with R13 batts (the yellow, extra scratchy variety)—with R19 batts under the windows. Roof is fairly new (just predates us at ~5 years), modified bitumen with silicone layer on top but no insulation on the deck that I’m aware of.

I had mini splits installed last year in response to an ailing 37 year old boiler (radiant baseboards) and the spike in energy use in the winter was shocking. Given the age of the house we’re exploring some insulation improvements which sent me down this road. 

From what I gather, common wisdom is that vented flat roofs are a thing of the past (especially with the small amount of venting we have). Also, from what I can tell we have a “cold roof”. 

If I’m understanding the Lstiburek article that everyone links it’s probably not worth doing anything with our roof insulation until we’re ready for a new roof—and at that point adding foam to the deck and dense packing the ceiling (or perhaps adding injection foam above our fiberglass batts?) and sealing the vents. Short of tearing out our ceilings that’s the only reasonable retrofit option I’ve gathered. And not the most practical until we need a new roof. Is that about right or am I off base? 

We got a quote to dense pack the walls and ceiling with cellulose. Given my research it seems the ceiling is a bad idea but the walls are a pretty safe bet…not the same bang that ceiling insulation would be…but significantly cheaper than redoing our roof. Would it be a waste to do the walls if the roof is a ways out? Or just a waste in general to go from R13 (though old batts) to ~R21) in the walls?

Any input is appreciated—many of the popular threads and articles I could find were 10+ years old. Hoping for practical advice to improving our current situation where possible without gutting the whole house!