I live in the United States, and as I understand it the housing crisis is caused by several factors.

1. The lowest level of zoning is typically residential single family. This means small scale owners and developers cannot increase supply by taking a house and adding to it. Either by adding extensions, subletting, or even building a mini-apartment building. To add to this, US regulations require apartment units to have access to 2 staircases, in the event of a fire. This is good fore safety, but greatly restricts style of apartments to hotel styles, and increases costs, so smaller apartments don’t make as much sense. This requirement should be able to be waved in the case of fire resistant building materials.

2. Speculative land owning. Some property owners simply sit on properties in developing areas, waiting for its price to increase, and since tax is based on the value of the total property (land+building), a decaying building reduces the cost of owning that land. To fix this, we should be taxing the value of the land instead, punishing speculators, while incentivising people to improve their land (by building housing).

3. Overuse of cars. Even when places want to expand housing, the complete and utter reliance on cars as transportation in the US leads to backlash for increasing housing, as the perception is that it will increase traffic. To combat this cities need to rethink their transportation strategies to radically increase things like bus and bike lanes. Even when cities do have buses, the strategy funded by the federal government is abysmal. For example instead of running buses that can hold 15 passengers and run every 15 mins, cities will instead run buses that can hold 50 people every hour, and so these buses run mostly empty with 2-3 passengers.