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Replacing existing garage with self-contained room (minor dwelling?)

I have an existing double garage (which has never been used as a garage - more of a storage room) that I would like to replace with a self-contained minor dwelling (ie like a granny flat - with open plan kitchenette in lounge area/bathroom/one bedroom). My property is on a cross lease title. I am wanting to know if this is possible under the current Auckland Council building laws.