Neighbor wants to build a semi-detached house with an offset

We are building a semi-detached house directly on the boundary. Our neighbor now wants to build later with an offset of over 1–2 m to us – so not directly adjoining. In conversation, we got the impression that he is not aware of the structural consequences of this decision. We have already completed the planning and building permit and want to start soon.

We are wondering how we can politely point out to him that the distance will cause significant additional risks and costs – for example:

[*]He needs his own fire wall and is not allowed to extend insulation, plaster, or roof parts over the boundary.
[*]The insulation of his boundary wall must still be fully installed and permanently protected – which will be difficult without overhang or sufficient working space.
[*]The resulting gap must remain tight, accessible, and maintainable – otherwise there is a risk of moisture problems, leaves, frost damage.
[*]Base, roof, and metalwork will become more complicated and expensive – on both sides.
[*]Our kitchen exhaust is located on this side – we do not want any problems with condensate or heat radiation on his wall.
[*]Overall, the offset causes costs that could be avoided by building directly attached.
Building Energy Act, BayBo, etc.

How can this be best addressed without giving the impression of interfering? We simply want to avoid future disputes and clarify who is liable for what if he chooses this solution.

Our neighbor now wants to build later with a setback of over 1–2 m from us – so not directly connected. In the conversation, we got the impression that the structural consequences of this decision are not known to him. We have already completed the planning and building permit process and want to start slowly. We are wondering how we can politely point out to him that the distance causes significant additional risks and costs [...]

Let’s assume the neighbor has nobler reasons than just being the biggest conceivable idiot. Then perhaps there is the naive thought behind it to protect himself by the offset so that you can’t watch the calories from his cream cake on the terrace ending up on your hips, which he paid for at the pastry shop. The offset as a "natural privacy screen" seems to me the most plausible reason for this nonsense. Personally, I would never ever come up with the idea to give away / cut off some of my potential house depth. And I suspect his idea will be history as soon as he realizes that a terrace must also lie within the building window. I hope he will in any case build on a slab (even if you do), because not only as a fellow basement owner does the later builder have to bring money for additional effort due to support. I honestly can’t imagine the neighbors and their successors to be any more extreme. So probably only harmless naivety of the kind "solid houses are more solid, prefabricated houses are more finished, and lemon butterflies fold lemons" is behind it. Let’s at least hope so!

Our neighbor now wants to build later with over 1–2 m offset from us – so not directly attached.

[*]Our kitchen exhaust is on this side – we don’t want any problems with condensate or heat radiation on his wall. [*]Overall, the offset causes costs that could be avoided by a direct attachment. Building Energy Act, BayBo, etc.

Can you sketch it? From the first sentence I had the impression he wants to build with a gap. Then kitchen exhaust on a wall towards the other semi-detached house?

can you sketch it? From the first sentence I got the impression that he wants to build with distance.

I rather think of complying with the extension obligation, but with underbite/overbite on the communal side.

Then kitchen ventilation on a wall to the other semi-detached house?

Even the professionals position a ventilation shaft on an "undivided own" exterior side.

we are building a semi-detached house directly on the border. Our neighbor now wants with over 1–2 m offset

Then everyone builds their own detached single-family house. That's how I understand it. So not: , but you on the border, then "nothing" and then the neighbor. So, the first question: Is he even allowed to do that or is only a semi-detached house permitted on the property? Definition of semi-detached house in the land use ordinance. If mandatory according to the development plan, then the matter is settled.

Just like , I also understood the OP that way, hence the question about a sketch.