It's a series of problems that confound each other, some artificial, some organic.
First, we have geography. Auckland is located on an isthmus that ranges from 1 km wide to 10 km wide. It's basically on an island. It's also covered in volcanoes. Wellington is bound by the sea on one side, and hills on the other. It's wedged in the middle. They can, and have, expanded into the sea using land reclamation, but there's only so much of that you can do. There's only so much land you can put buildings on, which is a major problem when growing.
NZ also suffers from NIMBYism. People in NZ don't want to live next door to apartments, and they also don't really want to live in apartments either. Everyone wants to live in a detached house with a back yard. This problem is particularly prevalent in Auckland. The poor state of public transport and congestion on the roads in Auckland also limits how far out you can live if you work in the CBD.
And lastly, the rate of immigration has been so high that they just can't build houses or infrastructure fast enough to keep up.
So these 3 factors have worked together to cause a severe housing shortage in Wellington and Auckland in particular.
Christchurch is the only city where house prices and rents are stable or decreasing. However, the city suffered a major earthquake in 2011 which knocked out a lot of the housing supply. Whole suburbs were razed, and will never be built on again. A lot of houses only needed remedial work, rather than full reconstructions, so the housing supply has bounced back reasonably quickly. Christchurch is also the only city of the 3 main cities in NZ that is built on flat plains. Christchurch has practically unlimited space to grow inland.
Most immigrants move to Auckland though, so Auckland has borne the brunt of this housing crisis.
I live in Christchurch and looking to buy a house here. There were so many dodgy repairs done after the quakes that there's a real risk of buying a lemon.
I have a friend where their foundations were repaired, turned out the builders had basically papered over the cracks. There are countless stories like this one.
I think the market in Christchurch is going to be very odd once the scale of these bad repairs comes out. New houses are definitely at a premium.
Christchurch was where I was looking at starting the business, having visited all of NZ’s major and most of the minor towns and cities - but it seems it’s not really a factor in their decision-making process.
There just simply aren't enough houses in NZ. Simply finding somewhere to live can be a struggle, let alone somewhere affordable.