I think there are probably two key channels we would focus on.
One is household consumption and the effects on wealth. In our model, households consume out of their labour income as well as their non-labour income, and increases in housing prices can feed through to wealth, which can support consumption. So a decline in housing prices could result in a decline in household consumption.
The other effect would potential be on residential investment as well. A sharp decline in housing prices could result in less investment.
Between the two, it's about two-thirds of the economy, so 30% would be fairly sizeable. It's hard to speculate.