Floor Area of your property

The term floor area has a legal definition as per the New Zealand building code.

“floor area, in relation to a building, means the floor area (expressed in square metres) of all interior spaces used for activities normally associated with domestic living”

This is in harmony with how calculations of “floor area” are on architectural drawings for building work. Commonly information from building plans is used when insurance is arranged. Floor Area is the term used in insurance contracts.

If you have legal plans of your property, (available from Council) you can rely on those figures.

Houses are insured on “Floor Area” not to be confused with area of house. Check your policy.
Having a 100m2 groundfloor and 10m2 room in roof cavity does not require insurance of 230m2 “Floor Area”. 
But 110m2 as per building plans.
House area is something that has appeared after the earthquakes. Check out the ANZ site here, second reference is to the building plans that is the correct one.
Then they offer you a guide to measure the outside.
What is the purpose of a Code of Conduct if they practice in this way.