That kinds depends on market conditions, who is buying and what is driving the market. In cities like SF, Boston, and New York, the overall vacancy rate is very

That kinds depends on market conditions, who is buying and what is driving the market. In cities like SF, Boston, and New York, the overall vacancy rate is very low but the luxury market is actually somewhat overbuilt, because that's what developers have the most incentive to build. In the Great Bubble, there was a higher vacancy rate and bigger disconnect between buying and renting, because there was so much construction that was driven by speculation.