It would be interesting to look at land value vs. labor requirements to build an additional floor. In the absence of regulations limiting building height, I th

It would be interesting to look at land value vs. labor requirements to build an additional floor. In the absence of regulations limiting building height, I think 70% is unlikely to become the norm. Just physically it seems likely that you could add 1000 square feet on top of a building for something that works out to less than 10 years worth of full-time labor. Assuming you amortize that over a 30 year mortgage, that's well under 50%. I could see a future in which land use regulations drive up the cost of housing to 70% of income. Also a future in which people work half the number of hours they do today and spend 70% of their income on housing, which is less of a nightmare scenario. There is a point where an additional floor becomes too expensive for the math to ever work out, but it seems to me the population of the Earth would have to more than triple for it to become as bad as you suggest.