Close the gap between the neighbor's house and our house

See photo

This is, apart from this , the only thing we know about your property; in the thread you have even completely spared pictures. What kind of clairvoyants are supposed to help you like that? For some people, "Schlauberg" is really what is written on the birth certificate. I can't believe it.

Who is supposed to install in the gap, the [Mainzelmännchen]?
That will only be possible from the neighbor's roof.
A sheet of metal on the high-rise wall that drains onto the lower roof, without a gap for rain to get in.

Who is supposed to install in the gap, the Mainzelmännchen?
That will only be possible from the neighbor's roof.
A sheet metal on the high-rise wall that drains onto the lower roof, without a gap for rain to get in

I would trust myself to glue in Styrodur and seal it on the right and left. For that, I would get into the gap.
Have sheet metal made, for that I would probably need a roofer.

Except for this , this is the only thing we know about your property, in the thread you even completely spared pictures. Which soothsayers are supposed to help you like that?
For some people, "know-it-all" is really written on their birth certificate. I can't believe it.

Thanks for the comment. I can make a lot of use of such a comment. Goes in the same direction as "know-it-all". Well, whatever.

So you only want to glue Styrodur on top? I believe this will not be a permanent solution; it would be more sensible to install a roof corner piece there with an appropriate sheet metal or a gutter. Because the question would be whether you are allowed to direct the water onto the neighbor's roof. If anything, I would do it properly or have it done properly. Ideally, it would also be good to either apply plaster to the wall or close the gap and possibly add insulation beforehand (but that should be assessed by a professional).

As already mentioned, a sheet metal is the simplest version, no roofer is needed for that. Titanium zinc sheets in L-shape are available at the hardware store, as well as a rail for sealing on the plaster of your house.

Thanks for the remark. I can make a lot of use of such a comment.

Can you or could you only? - apparently only could:

It goes in the same direction as smart aleck. Well, whatever.

Wrong, but you still have one more try.