"We just have infrastructure that's crumbling everywhere." Mayor Jill McLewis said it on the dais in January, casting the lone dissenting vote as the rest of the Sebastopol City Council approved a rule that let homeowners sell their accessory dwelling units as separate, individually owned homes. Everyone else in the room was celebrating a housing win. She was thinking about pipes.
Eight months later, her caveat is the part of the story that matters most if you actually own one of these units. The council vote made the sale legal. It did not make every ADU sellable. On a city and a county where private wells and septic systems still carry a large share of the housing stock, the system in your backyard, not the paperwork on file at City Hall, is usually what decides whether a condo conversion is realistic at all.
What The Ordinance Actually Changed
On a 4-1 vote in January 2026, Sebastopol became the first city in Sonoma County to opt into Assembly Bill 1033, the 2024 state law that lets local governments allow homeowners to convert an ADU into a legally separate condominium and sell it to its own buyer. Before this, state law required an ADU to travel with the main house on a single title, no matter how independent the unit actually was. Councilmember Phill Carter, who had campaigned on the issue, framed it as a way to convert existing granny units and future ones into a genuine ownership path for first-time buyers and downsizing seniors. Jen Klose of the housing advocacy group Generation Housing backed the move publicly, arguing that the long-term property tax revenue from new owner-occupied units would outweigh any one-time cost to the city.
Sebastopol was not the first city in California to opt in. San Jose moved first back in 2024 and completed the state's first ADU condo sale in the summer of 2026. But among Sonoma County's cities and unincorporated area, Sebastopol went first, and as of mid-2026 it remains one of only a handful of California cities to have adopted the law at all.
The Paperwork Path Nobody Skips
Once a city opts in, the mechanics of an actual conversion are procedural rather than optional. A homeowner working through an AB 1033 sale in Sebastopol has to clear each of these in sequence:
- A finished Certificate of Occupancy on the ADU before any condo map can be filed. You cannot run construction permitting and condo mapping side by side.
- Written consent from every lender holding a lien on the property before the condo map can be recorded.
- A condominium plan that complies with the Subdivision Map Act and the city's own subdivision rules.
- Formation of a homeowners association under the Davis-Stirling Common Interest Development Act, since a condo conversion legally requires shared-space governance even when the "shared space" is a driveway and a fence line.
- Final recording of all of the above with the county recorder before a sale can close.
City fees for the planning application run from $500 to $1,500, according to reporting in the Press Democrat. That number is manageable. It is also the smallest cost most sellers will face.
The Question The Celebration Skipped
Sebastopol runs its own municipal water system, drawn entirely from a handful of city wells inside city limits, according to the city's own water and wastewater page. That covers the homes and lots that sit within the incorporated city boundary. It says nothing about the acreage parcels, the country lots, and the older rural properties just outside city limits, where the ADUs with the most room to be genuinely separate from the main house tend to sit, and where the water and waste systems are private wells and septic fields, not a city main.
Permit Sonoma, the county division that reviews every well and septic application in the county, states plainly on its own site that Sonoma County's soils are notoriously poor for septic systems. That is not a marketing caveat. It is the reason the county runs an entire Operational Permit and Monitoring program for septic systems with supplemental treatment, requiring owners to submit self-monitoring reports every March and October, maintain a notarized easement allowing county inspectors onto the property, and renew the permit annually. Roughly 3,000 systems were recently released from that program under updated state rules, and roughly 1,150 remain enrolled, which tells you the county still treats a meaningful share of local septic systems as close enough to the edge of function that they need twice-a-year eyes on them, for a single household. That is before anyone tries to split the property into two legally separate, independently owned homes.
Why Splitting One Roof Into Two Owners Changes The Septic Math
A standard septic system is designed and permitted around one household's expected flow, tied to bedroom count and lot conditions at the time of installation. Condo-izing an ADU does not add plumbing fixtures overnight, but it does create two independent legal owners relying on infrastructure that was sized, financed, and inspected as a single unit. State well and septic rules set a 100-foot minimum separation between a private well and any septic tank or leach field as a common baseline, and Permit Sonoma's Well and Septic Division reviews every proposal that touches either system before signing off. A homeowner considering a sale under the new ordinance is not just asking a real estate attorney to draft condo documents. They are effectively asking the county to confirm that a system built for one deed can now legally serve two.
That question rarely gets asked before the legal and survey work starts, because the ordinance itself does not require it as a first step, the way a Certificate of Occupancy does. It becomes visible later, when a lender, a title company, or a buyer's inspector asks for septic records the seller assumed were settled.
Inside City Limits Versus Outside Them
| Inside Sebastopol city limits | Outside city limits, unincorporated Sonoma County | |
|---|---|---|
| Water and sewer | City-run municipal system, drawn from city wells | Private well and septic, overwhelmingly |
| Who reviews an ADU condo conversion | City of Sebastopol Planning Division | Permit Sonoma, but the county has not opted into AB 1033 |
| Can you sell an ADU separately today | Yes, if the property clears city process | Not yet, according to Permit Sonoma staff as of early 2026 |
Permit Sonoma program manager Genevieve Bertone confirmed to local reporters that the county has not opted in to implement AB 1033, even as some interest has been expressed by the Board of Supervisors. If your ADU sits on a parcel outside Sebastopol's incorporated boundary, the new rule simply does not apply to you yet, regardless of how solid your septic system is.
What This Means If You're Weighing A Sale This Year
Before spending money on a survey, a condominium plan, or HOA formation documents, the more useful first call is to Permit Sonoma's Well and Septic Division to pull whatever record exists for the parcel, including any past septic site evaluation. If the system has never been formally rated for two independently owned dwelling units, that gap is worth knowing before legal costs start accumulating. Statewide, AB 1033 condo conversions have run into the tens of thousands of dollars once surveying, civil engineering, and HOA paperwork are added together, according to reporting that tracked early conversions in other counties. Septic upgrades, if the system needs them, sit on top of that.
None of this means a Sebastopol ADU sale is impractical. It means the sequence matters. Zoning approval is the easy part now that the city has opted in. Confirming that the ground underneath the property can legally support two households is the part that decides whether the rest of the process is worth starting.
A Few Straight Answers
Does my ADU need its own septic system to be condo-ized? Not necessarily its own system, but the existing system's capacity and permit history need to hold up to scrutiny once the property has two separate legal owners instead of one. That review happens through Permit Sonoma, not through the city's condo paperwork.
What if my property is just outside Sebastopol's city limits? As of the most recent reporting, unincorporated Sonoma County has not adopted an AB 1033 ordinance, so a separate ADU sale is not currently available there even if the city right next door allows it.
Is this the same as renting my ADU? No. Long-term and short-term rental rules for ADUs are governed separately from AB 1033, and existing rental arrangements do not require any of the condo conversion steps described here.
How long does the process realistically take? Between the Certificate of Occupancy requirement, condo mapping, lienholder consent, and HOA formation, this is closer to a small subdivision than a simple paperwork filing. Plan in months, not weeks.
If you own a Sebastopol property with an ADU and you are trying to figure out whether a separate sale actually pencils out on your parcel, that is exactly the kind of question worth working through with someone who knows both the local market and the local permitting reality. Sold with Summer has spent years helping Sonoma County owners sort out what a property can and cannot support before they commit time and money to finding out the hard way. Let's talk about your next move.
