The term "Safe and Sanitary" came into existence after the first Building Act was introduced in 1992. There were specific sections in that act which made it clear that:
1. All building work required a building consent (there were exceptions, but they were very seldom relevant to domestic housing)
2. A building consent cannot be issued retrospectively.
3. Territorial Authorities (Councils) could declare buildings unsafe or insanitary, regardless of when they were built. This therefore applied to buildings or work built prior to July 1992 with or without what was then known as a building permit.
Many members of the public who owned buildings which had work done (including the construction of the complete building) without a building permit or building consent believed that they could get such "illegal" or "unauthorised" works legitimized by obtaining a "Safe and Sanitary Report". This is simply not true.
However, councils do have discretion whether to allow such unpermitted or unconsented building work to remain in place. Their main consideration was and still is, Is the work dangerous or insanitary?
In essence, "dangerous" means likely in the ordinary course of events to cause injury or death to any persons or damage to other property; or would give rise to almost certain loss of life in a fire (again, in essence).
"Insanitary" means situated or constructed or in such disrepair as to be offensive or likely to be injurious to health; subject to undue dampness or without adequate potable water or sanitary facilities (for the intended use).
Councils don't like illegal work and will not preclude the possibility of taking steps at some stage, but they will accept a report from a suitably experienced person, (usually an NZIBS member) and issue in reply a "letter of comfort", which has come to be called a "Safe and Sanitary Certificate", despite the fact that it is not a "certificate" at all (it is usually just a letter), is limited to the time of issue, is non-statutory (doesn't appear in any law) and is not a consent or guarantee.
What this means is that if the illegal work is not dangerous or insanitary, the council has better things to do than make you tear it down and rebuild, but they do retain the right to take further action at some stage in the future should they decide it has become necessary because the work has become dangerous or insanitary.