Joe Wilson's Silicon Valley Real Estate Blog

People buying homes in the country's most expensive housing markets likely will face pricier mortgages starting in the fall.

That's when the current conforming mortgage limits are scheduled to expire, with limits for the most expensive markets (Like the Silicon Valley) falling to $625,500 from $729,750. On Friday, however, two lawmakers introduced a bill in the House that would retain the higher limits for two years.

Mortgages over the conforming limit are considered jumbo loans, and can't be purchased and securitized by Fannie Mae or Freddie Mac. As such, they carry higher rates. The limits apply to both first mortgages and refinancings.

Limits vary by market, and the lower limits are equal to 115% of the median single-family home price, ranging from $417,000 to as much as $625,500.

"The fact that the limits are changing is going to raise the cost of home ownership for homes priced in that range between the old and the new limit," says Greg McBride, senior financial analyst for Bankrate.com. While the change is expected to officially take effect Oct. 1, it may be reflected in loan quotes as early as the end of July, he says.