The ratio of prices to rents is a sort of price/earnings ratio for the housing market. Just as the price of a share should equal the discounted present value of future dividends, so the price of a house should reflect the future benefits of ownership, either as rental income for an investor or the rent saved by an owner-occupier. To bring the ratio of prices to rents back to equilibrium, either rents must rise sharply or prices must fall. Yet central banks cannot allow rents to surge as this would feed into inflation. Rents directly or indirectly account for 29% of America's consumer-price index, so rising inflation would force the Fed to raise interest rates more swiftly, which could trigger a fall in house prices. Alternatively, if rents continue to rise at their current annual pace of 2.5%, house prices would need to remain flat for over ten years to bring America's ratio of house prices to rents back to its long-term norm. There is a clear risk prices might fall.I've been saying this for almost four years now, and I've missed out on some extraordinary equity appreciation. But, I am even more bearish today than I was four years ago and am actually renting my home today. If things do go south in real estate, I just hope it doesn't impact the rest of the economy too adversely.
Lower real interest rates might justify a higher p/e ratio. For example, real interest rates in Ireland and Spain were reduced significantly when these countries joined Europe's single currency—though not by enough to explain the whole rise in house prices. In Britain, where tax relief on interest payments has been scrapped, real after-tax rates are close to their average over the past 30 years, and so do not justify a higher price/rent ratio. In America, too, real post-tax interest rates are not historically low, in part because mortgage-interest tax relief is worth less at lower rates of inflation. For instance, if interest rates are 10%, tax relief is 30% and inflation is 7%, the real after-tax interest rate is 0%. If interest rates are 6% and inflation is 3% (ie, the same gap as before), and tax rates stays the same, the real interest rate is 1.2%.
TJ Jacobi points to an excellent article in The Economist on the imbalances of the housing markets throughout the world, and in particular the US. They discuss the ratio of house prices to rents and the unsustainability of the current market conditions.