Under Sonoma County rent increase laws, most landlords cannot raise rent by more than 7.7% for any increase taking effect between August 1, 2025, and July 31, 2026. That number comes from the statewide California Tenant Protection Act, which caps annual increases at 5% plus the regional cost-of-living change, with a hard ceiling of 10%.1California Attorney General. Know Your Rights as a California Tenant Mobilehome parks in Santa Rosa and unincorporated parts of the county face tighter local caps, and several categories of rental housing are exempt from the state cap entirely.
The Current Sonoma County Rent Cap
The California Tenant Protection Act, codified at Civil Code 1947.12, is the primary law governing rent increases in Sonoma County. It limits increases on covered units to 5% plus the regional change in the Consumer Price Index, or 10%, whichever is lower, in any 12-month period.2California Legislative Information. California Code CIV 1947.12 – Limitation on Rent Increases
Sonoma County is not part of the San Francisco Bay Area CPI region. It falls under the state’s “All Other Counties” category, which uses the statewide California Consumer Price Index published by the Department of Industrial Relations.1California Attorney General. Know Your Rights as a California Tenant The Attorney General’s office publishes an annual chart showing the maximum increase by region. The cost-of-living component is based on CPI data published each April, and the resulting cap applies to increases taking effect from August 1 through July 31 of the following year. For that current period, the Sonoma County maximum is 7.7%.
The math is straightforward. If your rent is $2,000 a month and the cap is 7.7%, the highest your landlord can charge after an increase is $2,154. A jump to $2,200 puts the extra $46 outside the cap and makes that portion unenforceable.
Two Increases Per Year and the Base Rent Rule
Even within the annual cap, a landlord cannot raise rent more than twice in any 12-month period, and the two increases combined still cannot exceed the annual maximum.2California Legislative Information. California Code CIV 1947.12 – Limitation on Rent Increases A 4% increase in March rules out another 5% in September when the annual ceiling is 7.7%.
The cap is measured against the lowest rent charged at any point during the prior 12 months. This blocks a landlord from temporarily inflating the base with fees or short-term adjustments before applying the percentage.
Which Units Are Exempt
Several categories of rental housing are not covered by the state cap:2California Legislative Information. California Code CIV 1947.12 – Limitation on Rent Increases
- New construction. Units that received a certificate of occupancy within the previous 15 years. It’s a rolling window, so a 2015 building loses the exemption in 2030.
- Single-family homes and condominiums. Units that can be sold separately from other dwellings, but only if the owner is not a corporation, a real estate investment trust, or an LLC with a corporate member, and only if the landlord has provided a specific written notice of the exemption to the tenant.
- Owner-occupied duplexes. A two-unit structure where the owner lives in one unit as a primary residence. Neither unit can be an accessory dwelling unit or junior accessory dwelling unit, and the owner must have occupied the unit at the start of the tenancy.
- Deed-restricted affordable housing. Units restricted by deed or a government agreement as affordable housing for low- or moderate-income households. A tenant simply holding a Housing Choice Voucher (Section 8) does not make a unit exempt.
The single-family and condo exemption trips up many landlords. It only works if the tenant received a written notice stating the property is exempt from Civil Code 1947.12 and Civil Code 1946.2. Without that notice, the exemption does not apply and the unit remains subject to both the rent cap and just cause eviction protections.2California Legislative Information. California Code CIV 1947.12 – Limitation on Rent Increases If you rent a single-family home in Sonoma County and never received that notice, the cap almost certainly applies to you.
Notice Requirements
A rent increase is not valid unless the landlord follows Civil Code 827. The notice period depends on the size of the increase:3California Legislative Information. California Code CIV 827 – Notice of Change in Terms of Lease
- 30 days’ notice for an increase of 10% or less of the rent charged at any time during the prior 12 months, including any other increases in that period.
- 90 days’ notice when the increase, by itself or combined with other increases in the prior 12 months, exceeds 10%.
The notice must be personally handed to the tenant or sent by mail following the procedures in the Code of Civil Procedure. A text, email, or verbal conversation does not qualify. Notice by email alone is not legally effective even if the tenant reads and responds to it.3California Legislative Information. California Code CIV 827 – Notice of Change in Terms of Lease When notice is served by mail, California law adds extra days to the notice period to account for delivery.
Mobilehome Park Rent Rules
Mobilehome owners rent the land under a home they own, so losing the space can mean losing the whole investment. Both Santa Rosa and unincorporated Sonoma County have local ordinances tighter than the statewide cap.
Unincorporated Sonoma County
Sonoma County Code Chapter 2, Article XIX limits annual space rent increases for mobilehome parks in unincorporated areas to 70% of the CPI change or 4%, whichever is less.4Sonoma County Legistar. Legislation Details – File 2023-1278 When a mobilehome changes hands through an on-site sale, the park owner may increase rent by up to 5% of the current base rent.
City of Santa Rosa
Santa Rosa City Code Chapter 6-66 sets a rent stabilization process specifically for mobilehome parks within the city, including a review procedure for proposed increases.5City of Santa Rosa, CA. City of Santa Rosa Code 6-66 – Rent Control, Mobilehomes Santa Rosa has no general residential rent control covering apartments or other rentals. Those units are governed by the statewide cap.
City of Petaluma
Petaluma also has no general rent control. It maintains a mobilehome park rent stabilization ordinance, but standard apartment and house rentals in Petaluma are subject only to the state cap.6City of Petaluma. Tenant Protection Details
Retaliatory Rent Increases
California law prohibits raising rent to punish a tenant for exercising legal rights. Under Civil Code 1942.5, if a landlord increases rent within 180 days of certain tenant actions, the law presumes the increase is retaliatory.7California Legislative Information. California Code CIV 1942.5 – Retaliatory Eviction Protected actions include:
- Complaining to the landlord about habitability problems
- Filing a complaint with a housing or code enforcement agency
- Reporting a suspected bed bug infestation
- Participating in a tenants’ association or exercising rights under the law
During that 180-day window, the burden shifts to the landlord to show the increase had a legitimate, unrelated reason. The law also prohibits threatening to report a tenant to immigration authorities as retaliation.7California Legislative Information. California Code CIV 1942.5 – Retaliatory Eviction A tenant can invoke the retaliation defense once in any 12-month period.
Security Deposit Increases
When rent goes up on a month-to-month tenancy, a landlord may also try to increase the security deposit. California allows this, but the total cannot exceed the statutory limit. Since July 1, 2024, the maximum security deposit for most residential tenancies is one month’s rent. A narrow exception applies to small landlords who are natural persons (not corporations or LLCs with corporate members) owning no more than two rental properties with a combined total of four or fewer units. They may collect up to two months’ rent.8California Legislative Information. California Code CIV 1950.5 – Security Deposits
A larger deposit collected before July 1, 2024, can stay in place at that original amount. Any increase requested after that date must comply with the current one-month cap, or two months for qualifying small landlords. The landlord must give at least 30 days’ written notice before the additional amount is due.
Challenging an Illegal Rent Increase
The Tenant Protection Act does not include built-in penalties against landlords who exceed the cap, so enforcement falls on tenants. If your landlord raises rent above the allowable maximum or skips the notice rules, you have a few practical options.
Start with a written letter to the landlord explaining that the increase exceeds the cap under Civil Code 1947.12. Show the math: your base rent, the applicable percentage, and the maximum allowable amount. Many smaller landlords do not know the cap exists, and a clear letter often settles the issue.
If the landlord refuses to correct the increase, you can contact a local tenant rights organization or the California Attorney General’s office, which publishes guidance on the Tenant Protection Act.1California Attorney General. Know Your Rights as a California Tenant You can also pursue civil remedies in court to recover overpaid rent. Small claims court handles disputes up to $10,000 without an attorney, which makes it a realistic path for most overcharge situations.
Keep every notice, payment record, and piece of correspondence. If the increase followed a habitability complaint or another protected action, the 180-day presumption under Civil Code 1942.5 strengthens your position. A landlord who raises rent right after you file a code complaint will have a hard time convincing a judge the timing was coincidental.