I read that link you mentioned about leaking buildings, but there is still more to be said about the regulatory regime (or lack of it) during those years.
The move here in the early 1990s was away from "prescriptive" to "light-handed" regulation of industry (sometimes referred to as "self-regulation"), in which the law stated what must be done, BUT ......... not how to do it. This was in accord with the Free Market ideas that were still dominant in business and government.
With regards to the weatherproofing of buildings, the 1992 Building Regulations only stipulated three things:
(i) That the building must be able to last for at least 50 years
(ii) That the roof must last for at least 15 years
(iii) That both walls and roof must be waterproof.
Nowhere did the 1992 regulations make any attempt to tell builders how to achieve these requirements. This was "Light-handed" Regulation in practice, leaving such matters to that buzz-phrase of the time, "individual choice".
The standard that you mention (NZS 3604) is not even cited in the 1992 Building Regulations. Rather than being a "Government" document, this and other such standards were compiled by the Standards Council of New Zealand - an organisation that fulfilled a similar role to the American National Standards Institute (ANSI). On their own, such standards had (and still have) no legal binding. That only takes place if the standard is stipulated in legislation.
For a very thoughtful discussion on this whole matter , Brian Easton's Regulatory Lessons from the Leaky Home Experience is a worthwhile read. (Easton is a well known New Zealand economist, who has been involved with the writing of more than 30 books. His observations about regulatory failure and the leaking building issue can be accessed on the following link. http://igps.victoria.ac.nz/publications/files/aea9bc2e751.pdf )
During those years of the late 1980s / early 1990s, attempts to implement Free-Market reforms in this country resulted in much mayhem, but failed to bring about economic recovery. One could certainly write a book about that on its own, and Prosperity Mislaid by Leonard Bayliss is one such informative work. (Again, Bayliss can write with considerable authority. A graduate of Cambridge University, he was an economist with the Reserve Bank for 15 years, before becoming the Chief Economist for the Bank of New Zealand, a position he held for a similar period. Later still, he served as a board member of that same bank).
Not that you need the likes of an economist to tell you about the mayhem that "Rogernomics" caused. You only need to drive around the former forestry towns in the Central North Island to see that some of its legacy is still ongoing (that is, if you are brave enough and your stomach is up to it!)
PS: During that same time, our industry (electrical) likewise went the "Light-handed" regulation way. Thankfully, though, they woke up to themselves in time before a similar disaster as this afflicted the electrical industry.