A COA is a far more formal process, time consuming and costly. There is no difference in the amount of information and detail required by a council as if you were applying for a building consent in the first instant.

Generally it is necessary to supply with the application a set of scale drawn plans, specification, product technical literature, producer statements (if Applicable) photographs and a report on the work by a suitably qualified building consultant. This report must provide supporting evidence that the building work complies with the appropriate sections of the NZ Building Code.

This is a more costly exercise and also more time consuming. There is a down side to this process and that is if the council cannot approve and issue the COA then the council must issue a Notice to Fix which is a formal notice under the Building Act 2004 requiring the works to be removed or remedial works to be undertaken. You can read about COA