The second vicious circle refers to the rising tide of homeowners with negative equity (Figure
4.3) which came about after the collapse of the US housing bubble. This bubble, as
other bubbles before it, was characterised by a rapid increase in the valuations of domestic
property until unsustainable levels were reached in relation to incomes and other measures of
affordability. A massive rise in household mortgage debt had arisen. A housing surplus was
generated by a combination of an oversupply of new homes and mortgage foreclosures. This
oversupply placed downward pressure on housing prices which lowered current homeowners’
equity. Homeowners with negative equity owed more on their mortgages than their properties
were worth. They were incentivised to default on their mortgage.