The 10 principles 'for an effective local retrofit collective buy-in scheme' outlined in the paper titled 'Local cooperations for district collective energy home retrofit' are:

1. You shall find the right people rather than the perfect homes to start such a movement.

2. You shall get local authority blessing for the initiative and audit homes with the same method.

3. You shall remember that size matters for better prices, but that it is smart to set different waves.

4. You shall invest in the power of grants and subsidies, which are most effective when public services are aligned with each other.

5. You shall set a clear calendar and provide an exit strategy to increase engagement.

6. You shall not forget to support the supply side to meet the grouped demand.

7. Setting projects with existing communities of trust makes implementation easier.

8. You shall bear in mind that doing things in a stepped way is fine. Some seeds will grow later.

9. Project leadership profile clarity matters, and easily replicable cooperative models work well.

10. You shall try not to be boring or overly technical, it is key to win hearts and minds.

The paper discusses the potential of applying community spirit to scale up home retrofits across the European Union. It highlights how districts built with similar methods could benefit from a standardised, efficient approach to retrofitting. 

While challenges like legal, technical, financial, and sociological issues exist, pioneers have already started tackling them. The EU's directive on building energy performance supports this effort, with initiatives like One-Stop Shops and Citizen-Led Renovation fostering community-driven solutions. The Energy Poverty Zero project aims to further this model in vulnerable districts, drawing lessons from existing pioneers and promoting local 'retrofit contagion dynamics'.