Silent has raised a whole new issue. The magic figure for owner/builders re warranty insurance is 6 1/2 years.
The usual procedure is to obtain a detailed report on the dwelling and then submit the peport plus details of any building permits and the relevant inspections to the insurance company. The insurance company will then decide how much premium you will need to pay. Not cheap!!!
If you are replacing damaged/old materials with new equivalent materials the work is considered as repairs. No building permit required and no warranty insurance
The notable exception is the re-stumping. This definitely requires a building permit.
Altering the structure in area or height (eg adding on a room) is not considered as repairs. Usually, demolishing a portion of the house and then re-building it is treated in the same way.
Talk to the building surveyor at your local council. His advice could save you grief further down the track.
Also talk to a planner at the council. There is a possibility that external alterations may also trigger the need for a planning permit. Especially going 2 storey.
As I said earlier, "It is really quite simple." :D :D