same case (terraced house), only I was the "injured party". We had it checked by a surveyor before starting the shell construction, and afterwards the neighbor did as well. The first suspected encroachment was about 5cm. In the end, something between 1-3cm. My lifetime was too valuable to me and the chances of success too unclear, even according to the architect. The following things annoy me to this day: - The shell builder on the other side and I discussed the planned distance of two cm (for the joint gap soft fiberboards) to the boundary twice and it was simply ignored, even after previous inquiry/notice. - My contact person is my neighbor and therefore I would have to sue him. The chain down to the shell builder is long, as is the duration, and both the general contractor and the shell builder know this. The relationship with the neighbor would then be slightly strained and the general contractor did not care. From my point of view, you have two options: - Simply ignore and wait to see what happens. - Have it surveyed and recommend the neighbor have the boundary surveyed as well. If a different distance to the house results, you can reach an agreement with the neighbor beforehand.