Excavating basement

[jingang li]

Hello,

If I want to excavate the basement approximately 50 cm, do I need to apply for a building permit? It's a villa.

And to excavate, does it mean that my basement wall extends 50 cm at the bottom?

Since the basement floor is excavated, all pipes should be reinstalled, is that correct?

Thanks in advance!

Rgds,
Jingang Li