The gap between homeowners and tenants isn't new. Orange County tenants have paid a greater share of their income for housing at least since 1990. Behind this trend is a basic economic fact about homeownership versus renting, explained Delores Conway of the University of Southern California's Lusk Center for Real Estate. While house payments may start out higher than rent payments, they can be fixed for 30 years or longer. And even adjustable mortgage payments have lifetime caps. But Orange County rents can increase annually, limited only by market forces. "Renters don't have much protection. They don't have fixed-rate loans that can lower their housing costs over time," Conway said. "So they are much more vulnerable."