ᐅ Neighbor plans to build a semi-detached house with a staggered layout

We are building a semi-detached house directly on the property boundary. Our neighbor now wants to build later with an offset of more than 1–2 meters (3–6 feet) from us – meaning not directly adjoining. In conversation, we had the impression that he is not fully aware of the construction-related consequences of this decision. We have already completed planning and obtained the building permit / planning permission, and we want to start soon.

We wonder how to kindly point out that this gap will cause significant additional risks and costs—for example:

- He will need a separate fire wall and is not allowed to extend insulation, plaster, or roof components beyond the property boundary.
- The insulation of his boundary wall must still be fully installed and permanently protected, which will be difficult without an overhang or sufficient working space.
- The gap that arises must remain sealed, accessible, and maintainable—otherwise, issues such as moisture, debris, and frost damage may occur.
- Base, roof, and metal flashing work will become more complicated and expensive on both sides.
- Our kitchen exhaust is located on that side, and we want to avoid problems with condensate or heat radiation affecting his wall.
- Overall, the offset creates costs that could be avoided with a direct adjoining build, considering regulations like the Building Energy Act, BayBo, and others.

What is the best way to approach this topic without giving the impression that we want to interfere? We simply want to avoid future disputes and clarify who is liable for what if he chooses this solution.