San Francisco’s rising home prices have been well documented over the years, but it’s not the only high expense homeowners are stuck with. Since the city has been hit with major earthquakes, most recently in 1989 and 1994, residents must pay, on top of their homeowners insurance, an earthquake rider, as the price increases every year, reports Daniel Goldstein of MarketWatch.

The expensive deductibles related to earthquake insurance are sometimes as high as 15% of the value of the home, which has many homeowners giving the insurance a second thought.

Premiums are determined by a combination of a home’s replacement value and its proximity to a high-risk fault. And for homeowners in Northern California, where some of the most valuable real estate in the country lies in an earthquake hot zone, that makes for an expensive financial double whammy.

The California Earthquake Authority (CEA) was set up in the aftermath of the two recent quakes in 1989 and 1994 to help provide low-cost insurance, after many property and casualty insurance companies pulled out following the quakes. From 1998, earthquake insurance premiums statewide rose from about $540 a year to $830 in 2005, according to the CEA. Now, those premiums average $800 a year.

However, in high-risk areas the costs are significantly higher. The average premium in 2014 on earthquake insurance for single-family homeowners in San Francisco County was $2,156; it was $1,800 in Alameda County (along the Hayward Fault) and nearly $1,000 in Los Angeles County, according to the CEA.

The number of earthquake insurance policies in California has dropped to just 10% of homes statewide, down from 34% in 1994, according to Risk Management Solutions, a Hayward, Calif.-based company.

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