Make housing less attractive as an investment vehicle. In my opinion the best way to do this is with the tax system (which, in NZ, currently favours property investment to a large extent).
Two proposals that are often discussed are a capital gains tax (CGT) and a land value tax (LVT). Personally I would prefer a LVT. A CGT would be an improvement on the current situation, but it would be a big impediment to freely moving to take up a new job or for family reasons. An LVT has the opposite problem of being a potential impediment to staying put if the value of your land increases relative to other areas. For an older person who is no longer working this could force them to find a new home but could be dealt with by deferring payments until sale or settlement of an estate.