He has a new paper (pdf) on this topic, with Jorda and Schularick, based on data from seventeen advanced economies since 1870. In an email he summarizes the main results as follows:
1. Mortgage lending was 1/3 of bank balance sheets about 100 years ago, but in the postwar era mortgage lending has now risen to 2/3, and rapidly so in recent decades.
2. Credit buildup is predictive of financial crisis events, but in the postwar era it is mortgage lending that is the strongest predictor of this outcome.
3. Credit buildup in expansions is predictive of deeper recessions, but in the postwar era it is mortgage lending that is the strongest predictor of this outcome as well.
Here is VoxEU coverage of the work. On a related topic, here is a new paper by Rognlie, Shleifer, and Simsek (pdf), on the hangover theory of investment, part of which is applied to real estate. It has some Austrian overtones but the main argument is combined with the zero lower bound idea as well.