While we have a good grip on developing new buildings that are green, old ones make up 80-90% of our usage. This is where we can make the real gains and this is where we should focus our policies. From an idea I posted on here a while ago: The UK government is set to ban gas boilers in new homes from 2025, with heating instead provided by low-carbon alternatives - e.g. heat pumps, heat networks and hydrogen boilers. However, as it stands, any existing UK home will be able to buy a gas boiler until 2035. 13 years away! Incentives to retrofit sustainable systems in existing buildings should be front and centre.