last time my neighbour built a brick wall beside our car porch wall from bottom to top with a 5 to 10 cm gap between our wall and theirs. It is an intermediate house so that gap instantly becomes a breeding place for rats and our side is not covered up till the ceiling so all sorts of pest is climbing over to our side. We can't do anything even talk to them and we did not raise our voice during the discussion, end up we have to sealed our wall but the gap unable to sealed because that is on their part of land.

shitty neighbour....bought a new house and move away.