The faults that govern San Mateo
The San Andreas runs the entire length of the county down the Peninsula — the Crystal Springs and San Andreas reservoirs sit in the fault's own valley, which is where it got its name. The San Gregorio fault runs along the coast through Half Moon Bay and offshore. The Hayward fault is across the Bay to the east.
Soils, slopes and site conditions in San Mateo
The eastern shoreline is Bay Mud and engineered fill: Foster City, Redwood Shores and parts of Belmont, San Mateo and East Palo Alto are built on it, and that ground both amplifies long-period shaking and carries liquefaction potential. The western hills along the Santa Cruz Mountains front include landslide terrain, and Daly City's coastal bluff neighborhoods have their own long-recorded instability, some of it exposed by the 1957 Daly City earthquake.
What San Mateo is actually built out of
The Peninsula's post-war identity is Henry Doelger and his imitators — 1940s and 1950s tract housing across Daly City, Westlake, South San Francisco and San Bruno, much of it built over garages. Pre-war raised-foundation homes fill Burlingame, San Mateo Park, San Carlos and older Redwood City. Foster City and Redwood Shores are 1960s to 1980s slab construction on engineered fill. Woodside, Portola Valley and Hillsborough carry high-value custom homes, and Portola Valley's town planning maps the fault trace right through the community.
Carriers price each of these differently. Wood frame on a bolted raised foundation is treated differently from slab-on-grade, post-and-pier carries the highest foundation surcharge in the standard model, and pre-1980 construction without documented retrofit faces an age surcharge that retrofit reduces but does not erase.
How San Mateo risk turns into a premium
The Peninsula has the highest ratio of insured value to house in California, and the San Andreas runs down the middle of it. A 15 percent deductible on a two-million-dollar rebuild is three hundred thousand dollars of retained loss — the deductible decision is effectively the whole conversation. Layer fill soils in Foster City and Redwood Shores, or a hillside lot in Woodside, on top of that, and the file becomes about site conditions and dollars rather than county tier.
- County risk factor: San Mateo County carries a high tier and a 1.34x multiplier against the CDI-anchored base rate.
- Dwelling limit: Premium scales with the earthquake dwelling limit, which should track your real rebuilding cost rather than your purchase price.
- Deductible: A 5% deductible costs roughly 42% more than a 15% baseline; 25% costs about 22% less. It is the largest lever you control.
- Construction type: Brick and masonry add roughly 38% to the base rate; wood frame sits slightly below baseline.
- Foundation type: Post-and-pier runs about 1.22x, raised about 1.08x, slab about 0.94x.
- Year built and retrofit: Pre-1980 raised-foundation homes without verified retrofit carry an age surcharge. Documented retrofit reduces it.
Choosing a deductible in San Mateo
Do the arithmetic in dollars before choosing. On Peninsula values the premium difference between 15 and 10 percent is frequently much smaller than the hundred-thousand-plus swing in retention. Homes on fill or on slopes may find the lowest options restricted, so confirm availability rather than assuming.
Remember that a percentage deductible applies to the dwelling limit, not to the claim. On a $750,000 limit, 15% is $112,500 you pay before coverage responds — whether the damage is $120,000 or $700,000. That is why the comparison has to be made in dollars.
What documentation is worth most in San Mateo
Doelger-era houses over garages should be evaluated for a ground-floor shear wall or frame; a permitted retrofit is the highest-value document available. The Burlingame and San Mateo Park pre-war stock needs bolting and cripple-wall bracing. On fill-soil addresses, any prior settlement, releveling or slab repair should be documented rather than discovered.
Partial documentation still helps. A permit showing bolting was completed, photographs of cripple wall work, or an Earthquake Brace + Bolt completion certificate all give an underwriter more confidence than a blank field. The application captures retrofit year, contractor, permit number and notes.
If you are buying earthquake coverage in San Mateo
Insist on an actual replacement cost estimate — Peninsula purchase prices are mostly land, and dwelling limits set from them are frequently far too low. Price 5 and 10 percent alongside 15. If you are in Portola Valley, Woodside or along the fault corridor, expect Alquist-Priolo fault-zone questions and have any geotechnical report ready. Foster City and Redwood Shores owners should raise the fill and Bay Mud question directly.
These are the San Mateo communities this page is written for: San Mateo, Redwood City, Daly City, Burlingame, Foster City, Menlo Park, Half Moon Bay, San Bruno, Hillsborough, Portola Valley, Woodside, San Carlos.
Before you start the application, gather your homeowners declarations page, year built, square footage and stories, foundation type, retrofit permits or certificates, water heater strapping status, masonry chimney condition, any prior earthquake or structural claim, and lender details if earthquake coverage is required by a mortgagee.
Related San Mateo coverage pages
Nearby counties we publish:
San Francisco · Santa Clara County · Santa Cruz County · Alameda County
Fault corridors that reach this county:
San Andreas Fault corridor
Coverage and underwriting guides that matter here:
High-value homes · Homes over one million · Liquefaction and fill · Homes over garages
Start wider:
All California county pages · California earthquake insurance guide · Deductible calculator · Carrier markets
Common questions about San Mateo earthquake insurance
Why is the deductible decision so important on the Peninsula?
Because earthquake deductibles are a percentage of the dwelling limit, and Peninsula dwelling limits are very large. Fifteen percent of a two-million-dollar rebuild cost is three hundred thousand dollars that you pay before coverage responds. The premium difference between deductible levels is usually far smaller than that swing, which is why it deserves an explicit comparison in dollars.
Is Foster City higher risk because it is built on fill?
Fill over Bay Mud amplifies shaking and carries liquefaction potential, and it is part of the underwriting review. Foster City's fill was engineered and the housing is comparatively modern slab construction, which helps. Prior settlement or slab repair history is the detail that most affects an individual submission.
Does standard homeowners insurance cover earthquake damage?
No. California homeowners policies (HO-3, HO-5) explicitly exclude earth movement including earthquake shaking. You need a separate earthquake policy for dwelling, contents, and loss-of-use coverage.
How is a percentage deductible calculated?
It applies to your insured dwelling limit — not the claim amount. A 15% deductible on an $800,000 home means $120,000 out of pocket before insurance responds, regardless of total damage. Use the calculator in the sidebar to see your number.
How long does it take to get coverage?
After submitting the application, a broker typically follows up the same business day with market options. Binding and policy issuance generally takes 1–5 business days depending on the carrier and whether additional documentation is needed.