* Introduce laws that make it harder to (legally) build housing. Note that much of New York would be illegal to build today, for instance.
* Use these laws to create scarcity. Ensure that there's never quite as much housing as people who need homes.
* Make massive amounts of debt available for said housing.
You now have an entire class of people who want to be sure their house only goes up in price, and that there is only just barely enough housing built to stop their region from collapsing. After all, who wants to be underwater on a mortgage?
I don't know how to break this on a policy level. Few people vote for the politician who says "I want your house to go down in price" so we get insane levels of rube-goldberg devices to make housing "more affordable" while also making it ever more expensive.
The more debt you make available, the more housing soaks it up. Sweden recently made the maximum mortgage length 105 years!
On the bright side, if you look at stuff that no bank will lend on (dilapidated structures, etc) there are some good deals to be had.