The low interest rate environment that has persisted in most developed economies since the financial crisis has led to increasing concern about accelerating house prices and increased household indebtedness in countries such as Australia, New Zealand, the United Kingdom and Canada.In Australia, interest rates are at historic lows, while house prices and household indebtedness are rapidly approaching historic highs, but so far no steps have been taken to address the latter. The Reserve Bank has expressed reluctance to introduce any form of quantitative control on mortgage lending, and remains cool on lifting interest rates while there is little sign the non-mining sectors of the economy might step up to counter the effects of the passing of the mining boom.There is also concern that any move to raise interest rates will result in appreciation of the currency, rather than a depreciation, which has been much talked about but not actively pursued.Last year, New Zealand found itself in the same position. The Reserve Bank of New Zealand was also loathe to raise interest rates at the time, but had no qualms about introducing quantitative controls on mortgage lending. From October 1 last year, no more than 10 per cent of bank mortgage lending could be allocated to home loans with high loan-to-valuation ratios (defined as loans greater than 80 per cent of the value of the property being lent against).Prior to the introduction of this quantitative restriction, approximately 25 per cent of new mortgages were classified as being high LVR. By the end of March this year, high LVR lending had fallen to 5.6 per cent of all new mortgages.Last month, the Bank of England announced that it would consult with UK mortgage lenders that lend more than £100 million a year, on the introduction of a different form of quantitative control. The Financial Policy Committee has recommended that from October 1 this year, new mortgage loans made to borrowers that exceed a loan-to-income ratio of 4.5 times should be restricted to no more than 15 per cent of all loans made.The use of a loan-to-income ratio directly targets the ability of a borrower to service their loan (among other considerations), rather than simply looking to the value of the property to cover a loan, once the borrower has defaulted. Also last month, Canada's Mortgage and Housing Corporation (the national provider of mortgage finance and insurance) announced that it would establish maximum house prices, amortisation periods and debt servicing ratios, effective from July 31, for its standard mortgage insurance product. The change is designed to increase market discipline in residential lending, while reducing taxpayers' exposure to the housing sector through CMHC. However, the latest country to implement controls on mortgage lending and thereby household indebtedness is Norway. And in typical Nordic fashion, the approach is quite different: greater capital discipline is being imposed on mortgage lending banks.Finanstilsynet, the financial supervisory authority of Norway, announced last week that it would change the way risk weightings are calculated for mortgages by banks using the