Here is basically a universal housing supply and demand curve for owned homes in a metro area. The difference between metro areas is where their supply curves fall. Closed Access cities have supply curves that are nearly vertical (inelastic) in any reasonable context. Open Access cities have supply curves that are reasonably flat (elastic) in any context that has been tested. And the Contagion cities generally look like Open Access cities, but they took on such huge in-migration from Closed Access cities that they reached their supply curve turning points. (As I have proceeded through the project, in some ways Miami has become a less than perfect fit as a Contagion city, but Florida in general fits the type, I think.)
The difference between these cities is their supply elasticity. Full stop. Closed Access cities have both short and long term inelastic supply, Contagion cities developed inelastic short term supply, but they have elastic long term supply (or at least, the demand curve moved back to the elastic portion of the supply curve when the Closed Access migration surge abated), and the Open Access cities have both short and long term elastic housing supply.
But, the irony is that, on the ground, changes in home prices are all going to be triggered by demand, because that's what is more volatile. So, rising rents, falling real long term interest rates, new tax benefits, etc. all create these volatile price shifts in Closed Access cities, and observers all say, "See! It's a demand problem!"
Let's say foreign buyers can avoid some sort of capital gains tax, and they start piling into closed access city real estate (because that's where capital gains expectations will be highest), and prices go up. Pass a law against foreign investment, and prices go down. See! It's a demand problem!
Or, a major shift in credit policies causes prices to rise or crash. See! It's a demand problem!
But, you usually don't hear about demand problems in Open Access cities. For some reason there is never a problem of excess foreign buyers in Dallas. Are there a lot of foreign buyers in Dallas? I don't know. Nobody cares. You want a house, they'll build you a house. Maybe there are more foreign buyers in Dallas than there are in Vancouver. Does anybody even bother to measure it?
How do you know if you live in a city with a housing supply problem? It will look like a city that has a demand problem. How do you know if your city doesn't have a housing supply problem? It won't look like it has a demand problem, even if its demand for new housing is twice the national average.