According to the Victorian Government then planning and building permits are handled at the local council level; there are no statewide rules for this. You will therefore need to contact your local council to find out the specific rules that apply to you.
From the link above:
Each local council has its own planning and building requirements, which must be met before they will issue a permit. You will need to contact your local council to find out what applies to your project.
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You will need to contact your local council to find out what local planning laws and regulations apply to your project.
If you let us know which council covers your area then someone may be able to provide more specific advice.
NB I do not live in Victoria, or indeed, anywhere else in Australia, so this answer is based purely on government websites and not any personal experience.