Retrofit - How is the sector approaching hard-to-treat homes?

The UK has the oldest housing stock in Europe and 5 million of these are social and affordable homes. These homes are integral to local communities, but retrofitting to get to net zero is a major problem. What are the broader options for improving the energy efficiency of ‘hard-to-treat’ homes? How should we approach housing that may not be ready to reach net zero by 2050? What is the future of stock rationalisation as we tackle building safety and net zero in tandem?