This isn’t true. I’ve lived in 3 places in London with single glazing. They’re surprisingly common. All new properties come with it but the majority of our housing stock is old.
There’s also little comparison between air con and double glazing. One will be helpful for 4-6 months of the year and reduce my energy bills. The other will be necessary at most 1-2 weeks a year and will cost me thousands of pounds up front. Most people simply can’t afford that.
