Too many people alterations and renovations are the same things, but they are not. A renovation is when the existing building is refreshed bringing it back to a new condition. For example new paint or wallpaper, or replacing the current bathroom fittings and linings. But an alteration goes further. It is where the structure of the building is changed. This will probably need a building consent but check with your council as some work is exempt. For examples see MBIE guidance on exempt building work.
If a building consent is required, one will only be granted for the alteration of an existing building, or part of an existing building, if the Territorial Authority (the Council) is satisfied that:
After the alteration, the building will comply, as nearly as is reasonably practicable, with the requirements of the building code that relate to –
(i) means of escape from fire; and
(ii) access and facilities for persons with disabilities (if it is a building type where this is required – see list);
AND the building will, –
(i) if it complied with the other requirements of the building code immediately before the building work began, continue to comply with those provisions; or
(ii) if it did not comply with the other requirements of the building code immediately before the building work began, continue to comply at least to the same extent as it did previously.
(See section 112 (1), Building Act 2004)
However, in some circumstances, the Council can issue a written notice to the owner that allows an alteration of an existing, or part of an existing, without the building complying with certain requirements of the building code, that have been identified by the Council, if the Council is satisfied that:
(a) if the building were required to comply, the alteration would not take place; and
(b) the alteration will result in improvements to the building that relate to –
(i) means of escape from fire; or
(ii) access and facilities for persons with disabilities; and
(c) the improvements referred to in (b) outweigh any loss, harm or damage that is likely to occur as a result of the building not complying with the relevant provisions of the building code.
(See section 112 (2), Building Act 2004)
An addition is where the footprint of the building is increased. This will most likely need a building consent and possibly resource consent. Check with your Council.