Illegal work is work that has been completed without the required permits (building and/or planning), or certificates or work that does not comply with the National Construction Code.
For example, if a builder has carried out notifiable work under the guise of “low risk” work that does not require a certificate of likely compliance and inspection by a building surveyor, this will be taken to be illegal work.
If an owner has failed to get a planning permit and employed a builder to construct an extension on their house which contravenes the planning scheme, this will be taken to be illegal work.
An owner builder has obtained the appropriate planning and building permits, but then not built in accordance with the NCC, this may also be illegal work.
Sometimes illegal work can be made to comply with the relevant legislation, but sometimes an order will be made to remove/demolish the illegal work.