Restrict the fiat finance of housing by for profit banks. Since neoliberal deregulation of the 1980s allowed for profit banks to fund housing housing prices have increased significantly. Only allow mutuals/non profit funders to finance housing. Problem solved. The free market does not work where fiat money is inherently not a free market- for profit bankers will pour vast sums into housing inflating the market in a self reinforcing cycle of rentseeking speculative debt based greed- and this is exactly what has happened since the 1980s neoliberal deregulation allowed them to.