According to the Federal Supreme Court, formally unlawful buildings that cannot be subsequently approved must in principle be removed (BGE 136 II 359 E. 6 p. 364).
In order for the property restriction to be permissible, it must be based on a legal foundation, be in the public interest and be proportionate, according to Art. 36 of the Federal Constitution. Thus, the restoration of the lawful condition may be waived if the deviation from what is permitted is only insignificant, the restoration is not in the public interest or the developer has acted in good faith and the continuation is not seriously contrary to the public interest.
However, only a bona fide developer can rely on proportionality. Those who did not act in good faith must as a rule carry out the demolition, because the authorities attach more weight to the public interest in the complete restoration of the lawful state in order to protect the equality of rights and the building order. Financial losses of the building owner are no longer taken into account. The Federal Supreme Court has clearly strengthened its case law in this regard, especially in the case of buildings and facilities outside the construction zone (cf. Federal Supreme Court ruling 1C_519/2020 of 28.10.2021 [Bee house in the high moor area on Pilatus LU]; in this sense already BGE 136 II 359 E. 9 p. 368 f. [LU]).