Check out affordability for sub-markets in New York, Los Angeles, Chicago, Washington DC, and San Francisco here.
Check your affordability before purchasing the house.
A spokesman for the regulator said: "We are concerned that lenders are, in effect, using CPAs to 'securitise' the loan, and so may not make adequate checks on affordability".
"Indeed, outside London and its commuter belt, demand may be better balanced with supply by the more stringent checks and affordability tests under the mortgage market review (MMR) that became mandatory less than a month ago.
Under the new rules, it will be the lenders, not the borrowers, who are checked by the regulator to ensure affordability checks for mortgage repayments are being carried out properly.
However, before allowing the switch, the lender is likely to do an affordability check.
If they want to remortgage to another lender, this will be even more difficult, as they will have to go through an affordability check, and the interest-only nature of the loan is likely to make the lender wary.
The Financial Conduct Authority (FCA) has proposed that all borrowers should have an "affordability" check before being given a loan.
The new system, which comes into force fully on 26 April, ensures that lenders conduct a full affordability check on mortgage applicants.
The industry has been referred to the Competition Commission and regulators have promised a tightening of the rules, with all borrowers set to be offered an "affordability" check before being given a loan.
