What's the Main Driver of Net Migration in New Zealand?

The number of people per houses has been changing in a structural sense but also in a short term sense. My understanding is that over the decades as family structures have changed and populations have aged we tend to have fewer people per dwelling. And from around I think it was early 2000s right up to the mid 2010s before we had a big boom in net migration towards New Zealand. That's important because if what that suggests is that if you have an increase in population you're going to need a larger supply housing supply response to meet that demand.