How close can a shed be placed to the property boundary?

Questioner

Terraced house, middle house. Back garden is approximately 60m2. At the back in the corner is a stone shed of 1.5m x 3m, shared roof with stone shed of the neighbors. Height is 2.3m. In front of the stone shed (10cm from the property line) is a wooden shed of 3m x 2.5m. Height is 2m. The 1.5m and the 3m are against the property line (although no line can be seen at the stone shed). Plan: replace wooden shed with shed/veranda on/against the property line of 4m x 3m. Height 2.3m, to be made equal to the height of the stone shed. So the neighbours will get a wooden wall of 4m on/against the property line instead of a wooden wall of 3m. Their sunlight will not/barely be reduced. As far as I know, this fits within the legal framework. According to the municipal site for permits, I should apply for an environmental permit. How is that possible? Am I mistaken?

Lawyer

No, I think that is mainly about the surface use of the garden now that there are two sheds, one of which may not have been registered and was already subject to a permit. On the property boundary it may not be four meters but a maximum of two.