Is the McMansion dead? At last week’s International Builders’ Show in Las Vegas, designer Marianne Cusato unveiled a 1,771-square-foot model home for 2010 that left many attendees with the feeling that, for homes, trim is in. The four-bedroom home has scarcely a foot of unusable space. The casual dining room can double as a formal one, while the extra bedroom can double as a home office or a rental apartment. It would cost an estimated $500 per year to heat and cool. “During the last decade, we saw a boom in housing sizes,” said Boyce Thompson, editorial director of Builder Magazine. “There was so much cheap money out there and anyone with a pulse could get it… builders, recognizing that everything was going to sell, paid way less attention to how the house actually operated,” he said. In the video above, MarketWatch takes a look inside Cusato’s vision for this year’s alternative to the McMansion.