It's been well analyzed, but shrinking household sizes means 1 new person needs more than a proportionate amount of new units, particularly since our shift away from sprawl to intensification means new units are much smaller and hold even fewer people than the types of units we built 15 years ago.
If housing was truly keeping up with demand, real affordability declines wouldn't be occurring at the scale they are.
I mean I don't get how you can look at a real estate market where most houses get 6-10 bids within the first 2 days of listing as not being in a shortage of supply. That takes some extreme level of delusion - either we cut demand or increase supply to level that playing field, or some combination of the two.
Our chosen planning policy regime naturally means that real declines in affordability in many product types are inevitable, particularly detached housing. That product is naturally going to become a true luxury product in the coming decades unless we decide to start building subdivisions en mass again.
Price increases can happen from a demand side from increased incomes, cheaper borrowing costs, etc., all of which have happened in the last 2 years (average incomes jumped, borrowing costs plummeted), without actually impacting real affordability. Then you have the Liberal's pushing immigration levels to their maximum, driving up demand even further, on top of the national level reversal of growth trends pushing growth into Ontario from where it was going in previous decades out to Alberta and Saskatchewan, and you get the problem we are in.
The question is why many feel real affordability is now being impacted. I genuinely believe our attempts to distort market demand with planning policy, pushing people away from the in-demand detached housing stock (which is what an estimated 60% of buyers would buy in an ideal condition) is creating extreme distortions in the market which are creating such a heightened sense of unaffordability.
It doesn't mean that we have to start sprawling again to fix it per se, the problem is that we've made is so that the only new supply we are allowed to build is extremely expensive concrete high rise construction with underground parking.. which is just extremely expensive. We have to find a way to build housing that is affordable per square foot again - which is what missing middle can do so well. Stick construction. low structural requirements, surface parking areas if it's provided at all, etc.
The regulatory environment needs to change to allow more low cost forms of construction. Whether that is missing middle, or making the US-style 5 over 1 apartment blocks more possible, or whatever, we need a way to construct a new unit for less than $1,000 a foot, and find a way to ensure that large amounts of residential floor space, regardless of unit numbers, is delivered every year.