I'm surprised that the Council can't help. Here in New Plymouth it is possible to get original building permit documents for houses in our district. I've actually done just that for a house we'd previously lived in so I could design a house based on the same floor plan.
Come to think of it I did the same thing for our current property (as did a draughtsman recently) to find drainage/septic tank locations, and prepare building renovation plans respectively.
Come to think of it I did the same thing for our current property (as did a draughtsman recently) to find drainage/septic tank locations, and prepare building renovation plans respectively.