Doing the math on affordability

As real estate prices in Metro Vancouver have risen toward the stratosphere, a public discussion about housing affordability seems to dominate water-cooler conversations.
For homeowners, affordable market housing means the maximum market price at which they could buy a home.
When I hear about new housing policies, I try to apply this definition to the proposed change so I can figure out who’s benefitting from a given policy and how, and determine whether the change improves affordability.