For private homes, a better solution is replace the roof with a new one that has more vents on the roof and better insulation qualities (e.g., California Title 24 regulations). The new roof on my house has cut the electric usage from 1005 kWh for June 2019 to 930 kWh for June 2020. Even with the current heat wave, my house now shuts down the air conditioner by 11 pm, instead of shutting down at 3-4 am!
Two years ago, I reroofed and added vented soffits. I use whirly gig turbine vents instead of a ridge vent (upon the advice of a building scientist friend of mine)
Last November, we added 12” of cellulose insulation to the ceiling. I also air sealed with 2 component spray foam everywhere I could reach without removing the existing insulation.
I haven’t compared all winter bills yet, but the first month was a 30% savings.
Air sealing makes a tremendous difference by completely encapsulating the walls and preventing small amounts of air infiltration from multiple locations.