Regulating Mortgage Leverage: Fire Sales, Foreclosure Spirals and Pecuniary Externalities

The US housing boom was accompanied by a rise in mortgage leverage. The subsequent bust was accompanied by a rise in foreclosure. This paper introduces a dynamic general equilibrium model to study how leverage and foreclosure affect house prices. The model shows how foreclosure sales, through their effect on housing supply, amplify and propagate house price drops. A calibration to match the bust shows consumption and housing need to be sufficiently complementary to fit the data. Since leverage plays a key role in foreclosure, a regulator can reduce systemic risk by placing a cap on leverage. Counterfactual experiments show that in a world with less leverage, the same economic shock leads to less foreclosure and less severe, shorter busts in house prices. A 90% cap on loan-to-value ratios in 2006 predicts house prices would have fallen 12% rather than 18% as in the data. The regulator faces a trade-off in that less leverage means less housing for constrained households, but also fewer foreclosures and less severe busts in house prices. A regulator with reasonable preference parameters would choose a cap of 95%.