Money and Risk | Tax and Insurance
Property Tax, Fire Zones and Insurance for a California Multiplex
Adding homes to a California lot changes three yearly costs: property tax, fire safety rules and insurance. This page explains how Proposition 13 taxes new construction, how the 2025 fire hazard maps affect what you can build, and what the California FAIR Plan covers when regular insurers will not. It uses the state constitution, the Revenue and Taxation Code, the Government Code and the California Department of Insurance as sources. For your own property, ask your county assessor and a licensed insurance broker.
Tax, fire and insurance in five facts
- When new construction is finished, the county assessor appraises it at full cash value on the completion date, through a supplemental assessment. Source: Revenue and Taxation Code 75.10
- When you add an ADU or a new home, the assessor sets a new base value only for the new construction; the rest of the property keeps its old base value. Source: Revenue and Taxation Code 70
- A city or county must adopt the State Fire Marshal's recommended fire hazard severity zones by ordinance within 120 days, may add or raise zones, and may not lower them. Source: Government Code 51179
- CAL FIRE released 2025 recommended fire hazard maps for Local Responsibility Areas starting in February 2025; the Los Angeles County maps were issued March 24, 2025. Source: CAL FIRE, 2025 maps for Los Angeles County
- The California FAIR Plan covers owners who cannot get insurance from a regular insurer, with limits of $3 million per location for residential policies and $20 million for commercial policies. Source: California Department of Insurance
Proposition 13 in Two Rules
Proposition 13 is Article XIII A of the California Constitution. Section 1 caps the general property tax: "The maximum amount of any ad valorem tax on real property shall not exceed One percent (1%) of the full cash value of such property." Ad valorem means based on value. Voter-approved bond debt is added on top of that 1 percent, so a tax bill can show a higher total rate.
Section 2 defines the value. Full cash value is "the appraised value of real property when purchased, newly constructed, or a change in ownership has occurred after the 1975 assessment." After that, "The full cash value base may reflect from year to year the inflationary rate not to exceed 2 percent for any given year." So the value the tax is based on can grow by at most 2 percent a year until the property is sold or new construction is added.
What Happens When You Build
New construction means any addition, or an alteration that is a major rehabilitation or converts the use. Under Revenue and Taxation Code 70 and 71: "The assessor shall determine the new base year value for the portion of any taxable real property which has been newly constructed. The base year value of the remainder of the property assessed, which did not undergo new construction, shall not be changed."
| Event | Tax result | Source |
|---|---|---|
| You buy the property | New base value at full cash value on the purchase date | Cal. Const. Art. XIII A, Sec. 2 |
| Each later year | Base value may rise by inflation, at most 2 percent a year | Cal. Const. Art. XIII A, Sec. 2(b) |
| You add an ADU, a second home or an addition | New base value for the new construction only; the rest keeps its old value | RTC 70(a)-(b), 71 |
| Construction is still underway on January 1 | Work in progress appraised at full value on that lien date | RTC 71 |
| Construction is finished | Assessor appraises the new construction on the completion date (supplemental assessment) | RTC 75.10 |
| You remove a structure | Counts as "actual physical new construction" | RTC 75.10 |
| You rebuild the same size after a disaster | Not new construction; only the part above the original gets a new base value | RTC 70(c) |
| You add seismic retrofitting | Excluded from "newly constructed" | Cal. Const. Art. XIII A, Sec. 2(a) |
For an owner who adds an ADU or a second SB 9 (2021) home, the result is simple. The existing house keeps its old base value. Only the new home is added at its value when finished, and the tax on that new value is 1 percent plus local voter-approved rates. Work underway on January 1, the lien date when property is valued for the tax year, is appraised at full value on that date. When the work is done, Revenue and Taxation Code 75.10 calls for a supplemental assessment as of the completion date, meaning a separate valuation of the new construction when it is finished.
Two details matter for a teardown. Section 75.10 says "actual physical new construction" includes "the removal of a structure from land," so demolition is itself an event the assessor looks at. And a building rebuilt after a disaster is treated differently: reconstruction that is "substantially equivalent" to what was destroyed is not new construction, and "only that portion that exceeds substantially equivalent reconstruction shall have a new base year value." Seismic retrofitting work is also left out of "newly constructed" under Article XIII A, Section 2(a).
Fire Hazard Severity Zones
Under Government Code 51178, the State Fire Marshal identifies moderate, high and very high fire hazard severity zones, based on fuel, slope, fire weather and wind. Under Government Code 51179, "A local agency shall designate, by ordinance, moderate, high, and very high fire hazard severity zones in its jurisdiction within 120 days of receiving recommendations from the State Fire Marshal." The city may add zones or raise their level, and may name a very high zone only with findings based on substantial evidence. It "shall not decrease the level of fire hazard severity zone as identified by the State Fire Marshal." The city sends its ordinance to the State Board of Forestry and Fire Protection within 30 days of adoption.
The maps changed in 2025. CAL FIRE's Office of the State Fire Marshal released 2025 recommended maps for Local Responsibility Areas starting in February 2025, and issued the Los Angeles County maps on "March 24, 2025, at 10:00 a.m. (PT)." CAL FIRE says properties in high or very high zones "may be subject to California Building Code Chapter 7A and defensible space requirements pursuant to Public Resources Code 4291." Defensible space rules, set in Public Resources Code 4291, cover the area around a building. Look up your parcel on the current map and confirm the zone with your city before you design.
How Fire Zones Change What You Can Build
A fire zone can remove a lot from the state's fast approval laws. SB 9 (2021) takes its site exclusions from the list in Government Code 65913.4, and HCD names "fire hazard areas" among the conditions that can disqualify a project. SB 684 excludes sites "Within a very high fire hazard severity zone," and also high and very high zones on state responsibility maps, under Government Code 66499.41. AB 1751, the townhome law that starts January 1, 2027, uses the same hazard exclusions.
ADUs are treated differently. HCD's ADU Handbook says: "The presence of a High Fire Hazard Severity Zone is not a conclusive rationale to warrant restricting ADUs." Cities add their own fire rules too. Berkeley's Middle Housing rules do not apply in the high fire hazard areas of the Berkeley Hills. Los Angeles excludes fire-prone hillside areas from its Low-Rise incentives. San Diego requires bonus-program ADU sites in high or very high zones to be on a public street with two evacuation routes and off a cul-de-sac.
Insurance and the California FAIR Plan
The California FAIR Plan is for owners "who cannot obtain insurance through a regular insurance company." The California Department of Insurance, which oversees it, says the Governor and Legislature created the FAIR Plan, and that it is a private association run day to day by insurance companies.
Coverage limits are "$3 million for residential policyholders and $20 million for commercial policies per location." The basic residential policy is a limited fire policy. Coverage for water damage, liability and theft needs a separate "Difference in Conditions" policy, until the FAIR Plan finishes a policy option that includes them. A multiplex owner on the FAIR Plan should price both policies together.
To apply, the Department says "you may contact the FAIR Plan directly at 800-339-4099. However, we recommend you contact a licensed insurance broker that is registered to sell FAIR Plan coverage." Ask your broker before you buy a lot whether regular insurers will cover it.
Selling Part of the Property
A sale resets the base value for what is sold. Article XIII A, Section 2 sets full cash value at the appraised value when a property is purchased or "a change in ownership has occurred." If you split a lot under SB 9 or SB 684 and sell one of the new lots, the buyer's lot gets a new base value at that sale. The same applies when an ADU or an SB 9 home is sold as a condominium under a local program, such as the ones San Jose and San Diego have adopted. The lot or home you keep is valued under the rules above: its old base value, plus a new base value for anything newly built.
Taxes and Insurance in Your Loan Payment
Lenders count property tax and insurance in the monthly housing payment they test. FHA calls it PITI: principal, interest, taxes and insurance. For a three- or four-unit property, FHA's Handbook 4000.1 says "The PITI divided by the monthly Net Self-Sufficiency Rental Income may not exceed 100 percent," and the lender must verify reserves equal to three months of PITI after closing. Fannie Mae subtracts PITIA (the same items plus homeowner association dues) from 75 percent of the gross rent when it counts rental income on a two- to four-unit home.
So a higher tax bill after new construction, or a FAIR Plan policy plus a Difference in Conditions policy, raises the payment the rent must cover. Get the assessor's view of the new value and a written insurance quote before you apply for the loan. The financing page explains the lender tests.
Best For
- ✓ Long-time owners adding an ADU or a second home, who keep the old base value on the existing house.
- ✓ Lots outside high and very high fire hazard severity zones.
- ✓ Owners who can get regular insurance and do not need the FAIR Plan.
Usually Fails When
- ✕ The lot falls in a very high fire hazard severity zone, which excludes SB 9 and SB 684.
- ✕ The budget leaves out the supplemental assessment that follows completion.
- ✕ Only FAIR Plan coverage is available and the budget assumed one regular policy.
What To Verify Before Spending Money
- → Your parcel's zone on the 2025 fire hazard maps, as your city adopted them.
- → With the county assessor, how the new construction will be valued.
- → With a licensed broker, which insurers will cover the finished multiplex.
Where to Go Next
Related on VanPlex: the Oakland and Berkeley page, where the Berkeley Hills fire areas are excluded, and the ADU law page.
Frequently Asked Questions
Does adding an ADU raise my property taxes in California?
How is new construction taxed under Prop 13 in California?
What is the Prop 13 property tax rate in California?
How much can assessed value rise each year in California?
What are fire hazard severity zones in California?
Did the California fire hazard maps change in 2025?
What is Chapter 7A in California?
What is the California FAIR Plan?
What is the California FAIR Plan coverage limit for a home?
Does the California FAIR Plan cover liability or theft?
Do fire zones stop SB 9 or ADUs in California?
Official sources (checked October 2026)
Planning a multiplex in California?
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