> At this rate

Be wary of any trend extrapolation. Better to figure out the dynamics underlying changes.

In this case, the rate will change way before rents have the chance to double. Rental markets are cyclical. In simple terms: They go up; they become unattractive to renters; they go back down.

There's no doubt that in many areas, including the San Francisco Bay Area, the current trend is not sustainable. But I think you're underestimating some fundamental shifts that have taken place that will put a floor under rents.

First, in the wake of the Great Recession, many folks are simply not able to buy homes. They can't meet more stringent lending standards and while there are efforts to make mortgages more accessible, a repeat of what you saw in the last housing bubble isn't likely any time soon. Making matters worse for folks still getting their financial footing is that home prices have appreciated considerably over the past several years.

Second, you need to consider demographics. Most young people can't afford to buy homes (more and more of them are living with their parents into their late 20s and 30s), and surveys indicate that home ownership is generally less important to younger people.

Finally, in some areas, including some of the most desirable parts of the Bay Area, there is realistically not going to be a significant increase in supply any time soon, so demand is likely to exceed supply for the foreseeable future.

Obviously, another recession would put a damper on things and double digit decreases in average rents are even possible in the hottest markets under such a scenario, but people waiting for $1,500 studio apartments in San Francisco shouldn't hold their breath.