Key legal question
Whether a backfilled wall is to be treated as a terrain alteration subject to setback rules under Art. 18 BauG.
Extracted holding
A backfilled wall is generally to be classified as a terrain alteration and must comply with the applicable setback requirements.
Extracted reasoning
Systematically, the wall referred to in Art. 18 paras. 3 and 5 is a boundary wall that must not be backfilled if it is to retain that function. Treating backfilling as terrain alteration avoids disadvantaging ordinary terrain modifications compared with walls filled behind.