Flow-Rider
Burner
It holds the heat in, I've lived in the house for than 30 years.The design of the house and orientation of windows vs North make a pretty big difference. A modern solar-passive design can work quite well even without huge amounts of insulation.
But I can't see how roof insulation is responsible for making your house warmer unless you have the windows and doors open all the time, and if that's how you prefer it with no air con then why install the insulation in the first place?
Because it's not cheap to have a decent solar system, speak to installers yourself because I have.Why is this relevant to the bigger picture?
You would find the same type of stats for motor mechanics and smash repairers.