The McMansion may be shrinking.

With the nation's housing market in a slump and the mortgage market in disarray, many home builders are putting up fewer supersize homes and offering smaller floor plans. That seems to be what buyers suddenly want in an era of high prices and tougher financing.

"Financing has tightened down so much that many people aren't able to qualify for the larger houses," said Kathryn Boyce, an account executive in Northern California for Boston-based real-estate research firm Hanley Wood Market Intelligence. "Throughout the U.S. people can't afford what they previously did. Floor plans are going to get smaller."

Home sales have plunged over the past year, leaving builders saddled with excess inventory, especially of larger, more expensive homes. In July, new-home sales were running at a seasonally adjusted annual rate of 870,000 units, down sharply from 1.3 million in 2005.

More recently, turmoil in the mortgage market has made it harder for buyers to qualify for bigger loans. As lending standards get stiffer, lenders have cut back on mortgages exceeding $417,000. That's the maximum size loan that lenders can sell to Fannie Mae and Freddie Mac, the government-sponsored financiers that buy mortgages from lenders and repackage them into mortgage bonds for sale to investors.