> Take a look at the first figure (HM1.1.1) in the following document - particularly those for the US, Canada, Australia, and NZ (all countries with prominent housing issues).

These are country-wide numbers. The obvious problem is that there is existing housing in Detroit but demand for housing in San Francisco.

It's also somewhat self-defining. If millennials are forced to live with their parents because they can't afford their own home then this is counted as one "household" when there is demand for two.

> On the other hand, I think there is a strong argument to be made for increasing underutilisation of housing (more second homes, short term rentals, etc).

There isn't anything inherently wrong with short-term rentals or second homes, they're just another type of housing demand that requires supply to increase to compensate. Until it isn't allowed to.