It's actually quite easy. The key things to know are 1) that the majority of house purchases are made via mortgage lending, and that 2) an excess of bank lending over bank loan repayment causes money creation.
So first determine if there is an abnormally high increase in the supply of money occurring - if yes, then there is a bubble, and if not, then the increase is probably the normal one that would be expected as a result of fiscal expansion. This is fairly easy to determine by simply looking at relevant statistics for the amount of money being held in bank deposits (typically M2 or M3, the precise definitions vary between countries).
The key thing to appreciate, is that because of the normal expansion of the money supply by the banking system over time, and especially because that money directly influences house prices, an increase in house prices over long periods is to be expected simply due to the operation of the banking system. Only if economic conditions really deteriorate. i.e. Detroit does this not occur. Regulatory changes, or even simple changes in custom and practice around the amount of lending can quite easily trigger changes in fiscal expansion, for example if the banks change from requiring a 20% deposit to a 10% deposit on house purchase.
It is also possible for house lending to increase without an abnormal increase in the money supply - in particular the 2008 crash in the USA, and elsewhere, was caused by an increase in lending as a result of the huge increase in securitized bank loans. This had the interesting effect of increasing the amount of lending originating in the banking system (and then being moved outside it), without increasing the money supply. This also made it at the time, somewhat invisible, subsequently the US and other countries have introduced statistics on securitization that allow it to be tracked.
Generally speaking, changes that also increase the money supply will cause a much bigger price rise, than changes that only increase the amount of lending, but the entire system is significantly leveraged, leading to some highly non-linear impulse responses at times.
So if we look at the New Zealand figures:
New Zealand Money Supply
It looks like the Money Supply flat lined following the 2008 crash for 3 years, and has now returned to something approximating its "normal" rate of expansion, which would explain the perception of a bubble. (What the normal rate of monetary expansion should be is an open research question.) It doesn't look like there are separate securitization statistics, and there probably isn't much loan securitization, but it's something to keep an eye on.