Mansionization: Coming Soon To A Neighborhood Near You?; Trend Is To Supersize Houses It can help home values, but also spurs worry over how big and small coexist

Although mansionization can increase values, preservation also offers incentives. The Los Angeles Conservancy created 21 historic zones in which exteriors of all homes must be preserved. Christian Redfearn, professor at the University of Southern California's Lusk Center for Real Estate, notes that some historic-zone houses are valued 7% to 8% above identical ones just outside the zones.

"Wealthy home buyers will pay a premium to ensure that the character of their neighborhood is preserved," Redfearn said.