They are also extremely badly insulated and costly to heat, having solid brick walls, large windows and high ceilings. We've already picked the low-hanging fruit like loft insulation and double glazed windows.

What's left to do is things like exterior cladding. I looked at getting external insulation applied to a victorian terraced house, and was quoted £30,000 - more than the UK's median salary.

The average annual energy bill is £1,923 so even if that insulation was so effective it dropped the energy bill to zero, it'd still be a pretty bad investment.

Even my grandma's summer cabin has double glazed windows and it's not liveable during winters in the least. =)

Over here triple-glazing is the minimum and has been for decades, I don't see why it wouldn't be useful everywhere else too. They keep the heat out during summers and the heat in during winter.

Unfortunately, having more panes of glass does not automatically mean you get more energy efficiency.

The triples with very good insulation and coatings (eg. heat rejection) can be better than old quadruples. My parents have quadruple windows from the 80's, and energy efficiency is much better in a modern triple single unit than with the two doubles they have.

That would be what, like 7% return on investment? We just had a period of ~0% interest rates and <2% mortgage rates.

It is not realistic to expect ROI of only a few years for upgrades to buildings or infrastructure. Lifespan of these things is like half a century or more.

Coming from eastern Europe, the age and condition of housing here was a bit shocking.

There used to be a grant in UK for insulating housing, and it was cut by conservative government. Our rate of insulating homes dropped form 2 million houses a year to basically zero. Without favourable credit, maybe zero interest credit, avaliable, of course individual homeowners will find it difficult to afford.