In France, Italy, Spain and Belgium the cost of selling one house and buying another (estate-agent fees, stamp duty and legal fees) often amounts to more than 15% of the price of a home.

ECONOMIST: When home is a prison

Mr. Warner, of Alchemy Architects, was commissioned to build the couple's house for the prior owner, a real-estate agent, though he has since become good friends with Ms. Feldman and Mr. Lutz.

WSJ: Minneapolis Luxury Real Estate: A Big Version of a 'weeHouse'

"We can list a house and in two hours have an offer, " says Beth Ferester, a real-estate agent in Houston.

WSJ: From Oil, a Land Rush��WSJ Mansion