Facade insulation for a semi-detached house: what/how must be approved by neighbors?

Hello dear forum members,

I have some questions regarding the renovation of my semi-detached house that I am planning and hope you can assist me with.
I want to have my own semi-detached house insulated according to KfW standards.
According to the partition declaration, the two semi-detached houses are completely separated from each other legally.
However, in my case, the roof must be extended (about 2-3 rows of tiles) so that the insulation is also protected from above.
In doing so, the roof valley on my side and my neighbor’s side must be adjusted so that rainwater can continue to flow off.
Additionally, the plasterer recommends attaching the insulation a little (about 50 cm) beyond my own boundary to the neighbor in order to prevent thermal bridges.

For what do I need the neighbor’s permission? How must it look?
Is there a possible template letter here in the forum that one could use as a guide for wording?

Thank you in advance for any possible answers.

Thanks

Simply asking the neighbor (after knowing what you would legally have to do) if he might also be interested in insulation? This way it becomes somewhat cheaper for everyone... The scaffolder covers the setup and takedown for the entire house. The roofer as well. The plasterer....and so on... Of course, the neighbor has to have the corresponding money....

In the process, I would also give him an invoice for the planned energy savings right away...

In which federal state is the facade being done?

I have already spoken with the neighbor. He has no interest in insulating the facade. He believes that insulation automatically means mold in the house )) Built in 1985 in Baden-Württemberg.

May I ask what the insulation (komplett) costs and how high the previous heating costs (preferably excluding hot water generation) are per year?

You may not put even an iota of insulation onto his property side without his consent.

"The Oberlandesgericht Karlsruhe has ruled that thermal insulation may not extend onto the neighboring property, reports the ARGE Baurecht."

So, if he says yes, then only in writing and preferably have it registered in the land register. Otherwise, a later owner might come along and say it has to be removed from his land.

The insulation including roof extension costs 21K. Heating costs are currently 1300 € per year. Thank you for the information. Do I also need a land register entry if it is only about the topic "roof gutter" for rainwater? The 50cm from the neighbor is only a recommendation from the plasterer. But it is not a must!