The need for a building permit for a retaining wall in Australia depends on the specific regulations set by local councils or authorities.
Generally, a permit is required if the wall exceeds a certain height or if it is considered a structural retaining wall.
The height threshold for permits can vary between states and councils, ranging from around 600mm to 1,000mm.
It is essential to consult with the local council or building authority to determine the specific requirements and obtain the necessary permits before commencing construction.