Unpermitted ADUs in California: Disclose, Legalize or Sell As Is
An unpermitted ADU in California is a second unit or conversion that was built or altered without the building permits and final inspection it needed, and selling a home that has one is legal as long as you disclose it. State law now gives owners of units built before January 1, 2020 a realistic way to legalize them, and a separate way to ask for a five-year delay before building-code violations are enforced. Neither happens automatically, and neither changes what you must tell a buyer.
This guide is for sellers deciding what to do with a garage conversion, a converted barn or a backyard cottage with a kitchen that never got a permit, and for buyers sizing one up. It covers the disclosure duty, the three practical paths before a sale, how legalization and delayed enforcement work as of October 2026, and how lenders and appraisers look at the unit. It sits within our home selling process guides.
What makes an ADU “unpermitted”
The question isn’t whether the space looks finished. It’s whether the city or county approved it as a dwelling and signed off on the work. Common North Bay examples include:
- A garage turned into a studio with a kitchenette and bathroom, with no conversion permit.
- A detached “guest house” or pool house that was permitted as an accessory structure, then had a kitchen added later.
- A permitted ADU whose permit was never finaled, or that was enlarged beyond the approved plans.
- Older second units built decades ago, before anyone on the current title owned the property.
Start by pulling the permit history from the building department that has jurisdiction, then compare it with the assessor’s record and with what is actually on the lot. Our post on guest houses in Napa, Sonoma and Marin explains how county definitions of guest houses and ADUs differ, which often decides whether a structure is a permitted accessory building or an unpermitted dwelling.
The construction date matters more than most owners expect. The state legalization and delay rules turn on whether the unit existed before January 1, 2020, so dated photos, old invoices, aerial images and assessor records are worth collecting now.
What a seller has to disclose
California’s Real Estate Transfer Disclosure Statement (TDS) asks the seller directly about this. In the version of the form reproduced in the Department of Real Estate’s disclosure booklet, the seller answers yes or no to whether there are room additions, structural modifications or other alterations or repairs made without necessary permits, whether any such work is not in compliance with building codes, and whether there are zoning violations or nonconforming uses.
If you know the unit was built without permits, say so on the form and in plain words in your supplemental disclosures. Describe what you know: when it was built, by whom, whether utilities are shared, and whether anyone has lived in it. “Seller makes no representation” language doesn’t replace an answer to a question you know the answer to. Our guide to California seller disclosures covers the full set of forms and deadlines.
Marketing should match the disclosures. Describe the space as what it is, such as “detached studio, not permitted as a dwelling,” and don’t present it as a legal second unit or quote its rent as legal income unless you have the paperwork. Selling “as is” limits repair negotiations; it doesn’t limit disclosure, as our guide to selling as is in California explains.
If you’re selling as an executor, administrator or trustee, ask your attorney which disclosure forms apply to your sale; Diamond handles probate and trust sales and can tell you what buyers will ask for.
Three paths before you list
Most sellers end up choosing one of three approaches. The right one depends on the unit’s condition, how much time you have and who the likely buyers are.
| Path | What it involves | Best fit | Main risk |
|---|---|---|---|
| Legalize first | Apply to permit the existing unit, open walls if inspectors require it, make corrections, get a final | Units built before 2020 in fair condition, sellers with several months | Corrections cost more than expected; the timeline slips past your listing date |
| Disclose and sell as is | Full written disclosure, permit history in the disclosure package, pricing that reflects the unit’s status | Sellers who need a sale soon; buyers who want a project | Smaller buyer pool, especially for financed buyers; appraisal may give the unit little value |
| Restore the original use | Remove the kitchen or other features so the space returns to its permitted use, with any permits that requires | Unsafe units, or units that can’t meet health and safety standards | Loses the living space; a buyer may still ask what was done and when |
A pre-listing inspection that treats the unit as its own dwelling is usually the best first step, because it tells you which path is realistic before you spend money on any of them.
Legalizing a unit built before 2020
Government Code section 66332 is the main legalization rule. For an unpermitted ADU built before January 1, 2020, a local agency can’t deny a permit to legalize it because it violates building standards or doesn’t meet the state or local ADU rules. The agency can still deny it if correcting a violation is necessary to meet the substandard-housing standards in Health and Safety Code section 17920.3, and the protection doesn’t apply to a building deemed substandard under that section.
Legalizing the unit generally can’t trigger impact fees or utility connection and capacity charges, unless utility work is needed to meet those health and safety standards or a fee is one that section 66324(e) allows. The agency may inspect and recommend corrections, but it can’t penalize the applicant for having built without a permit, and it must publish a checklist of substandard conditions and tell owners they may get a confidential inspection from a licensed contractor first.
A typical sequence looks like this:
- Gather evidence of the construction date: assessor records, old permits for other work, dated photos and contractor invoices.
- Hire a licensed contractor for a confidential pre-application inspection against the agency’s substandard-housing checklist.
- Decide whether to proceed. If the checklist shows serious health or safety problems, budget for those corrections first.
- Apply with plans that show the unit as built, plus the construction-date evidence.
- Pass the agency’s inspection, make required corrections and get the final sign-off.
Napa County’s ADU page shows how one agency applies this. It describes the program as a streamlined pathway for units in unincorporated Napa County that sit on a parcel with a permitted single-family home and were built before 2020, and it says significant unpermitted work after January 1, 2020 doesn’t qualify. The county asks for a letter of intent with construction-date evidence and a signed checklist from the owner’s contractor, waives impact fees for qualifying units, and charges a code investigation fee of 400% of the standard inspection fee, which it describes as cost recovery rather than a penalty. It says it processes these applications within 60 days of a complete submittal, though complex cases can take longer.
Other jurisdictions run their own versions; in San Francisco, see our page on unwarranted units. For rural parcels in Sonoma County, septic and water capacity often decide what can be approved; see our post on land, building lots and ADUs in Sonoma County. Diamond may refer you to partners we work with, such as contractors and inspectors; you’re free to choose any provider.
Delayed enforcement: five years, not a permit
Separate from legalization, Government Code section 66331 lets the owner of an ADU ask the local agency to delay enforcing a building standard. It covers units built before January 1, 2020, and units built later in a jurisdiction whose ADU ordinance didn’t comply with state law at the time, provided the ordinance complies when the owner asks.
The details are in Health and Safety Code section 17980.12, last amended effective January 1, 2025. An agency that issues a notice to correct a violation on a qualifying ADU must tell the owner a delay can be requested. The owner may apply for a five-year delay on the ground that correcting the violation isn’t necessary to protect health and safety, and the agency must grant it if it agrees, after consulting the agency that enforces State Fire Marshal building standards.
Two dates matter. Agencies can’t approve new delay applications on or after January 1, 2030, though delays approved before then run their full term, and the section itself is repealed on January 1, 2035. A delay gives an owner time; it doesn’t legalize the unit, and a buyer inherits a delay that will end.
How buyers, lenders and appraisers treat the unit
A financed buyer’s lender, and the appraiser it hires, will look closely at the unit. Fannie Mae’s Selling Guide topic B2-3-04 (dated October 8, 2025) says an ADU should be considered legal if the current zoning code allows it. If an ADU isn’t allowed under zoning in any circumstance, the property is eligible only if the lender confirms the ADU won’t jeopardize a future insurance claim and the appraisal meets the zoning requirements of topic B4-1.3-05.
That topic speaks to zoning, not permits, and lenders can add their own conditions, so expect questions about permit status either way. The appraiser also decides whether the property is a one-unit home with an ADU or a two-to-four-unit property, looking at things like separate meters, a separate address and whether the unit can legally be rented.
Rent is a separate test. Under topic B3-3.8-02 (dated September 2, 2026), only one existing ADU on a one-unit primary residence can produce qualifying rent, and only on a purchase or limited cash-out refinance; the lender uses 75% of gross rent, and ADU income can’t exceed 30% of the borrower’s qualifying income. Lenders can add their own conditions and may decline to count rent from a unit without permits, so a seller shouldn’t assume a buyer can use it to qualify. Our guide to buying a home with an ADU covers the buyer’s side, and our comparative market analysis explains how we price around space that comparables may not support.
Tenants living in an unpermitted unit
If someone rents the unit now, treat it as a residential tenancy for planning purposes. Permit status doesn’t make the tenant go away, and an unpermitted unit can raise its own questions about habitability, rent already collected and what happens if the unit must be vacated for corrections. State rent and eviction rules, explained in our guide to AB 1482 for landlords, and any local ordinance may also apply.
Get advice from a landlord-tenant attorney before you give notice, raise rent or promise a buyer the unit will be delivered vacant. Our page on selling a tenant-occupied home explains how occupied listings are shown and closed.
Can the ADU be sold separately?
Only after it’s legal, and only where the city or county allows it. Government Code section 66342 lets a local agency adopt an ordinance allowing an ADU and the main house to be sold as separate condominiums. The ordinance must require a safety inspection before the condominium plan records, shown by a certificate of occupancy or a housing quality standards report from a HUD-certified inspector, along with lienholder consent and notice to utilities. An unpermitted unit can’t meet that inspection step until it’s legalized. Our ADU investment guide lists the local programs we’ve confirmed.
This page is general information, not legal advice. Before you list or buy a home with an unpermitted unit, have a California real estate attorney review your disclosures and any tenancy, and ask the building department which legalization path fits that parcel.
Questions people ask
Can I sell a house with an unpermitted ADU in California?
Yes. There’s no rule against selling it, but you must disclose what you know about the unpermitted work on the Transfer Disclosure Statement and in your other disclosures, and the price should reflect the unit’s status.
Is there an amnesty program for unpermitted ADUs?
Not a blanket amnesty. For units built before January 1, 2020, Government Code section 66332 limits when an agency can deny a legalization permit and bars penalties for the original lack of a permit, but the unit must still pass inspection and meet health and safety standards.
How long does it take to legalize an unpermitted ADU?
It depends on the agency and the corrections. Napa County, for example, says it processes these applications within 60 days of a complete submittal, while design work, contractor scheduling and corrections can add months.
What does the five-year delay in enforcement do?
It postpones enforcement of a building standard on a qualifying ADU when correcting the violation isn’t needed to protect health and safety. New delays can’t be approved on or after January 1, 2030, and a delay doesn’t make the unit legal.
Will a buyer’s lender count rent from an unpermitted ADU?
Don’t count on it. Fannie Mae allows ADU rent only within strict limits, and a lender may decline to use rent from a unit without permits. Ask the buyer’s lender early.
Should I legalize the ADU before selling?
If the unit was built before 2020, is in fair condition and you have several months, legalizing it can widen your buyer pool. If it needs major health and safety work or you need to sell soon, full disclosure and pricing it as a project may make more sense.
Does the 2020 date apply to units built after that?
Generally the legalization and delay rules cover units built before January 1, 2020. Delayed enforcement can also cover a later unit built where the local ADU ordinance didn’t comply with state law at the time.
If you’re preparing to sell a home with a second unit and aren’t sure what you have, start with a home valuation that accounts for the unit’s status, and we’ll help you decide between legalizing, disclosing and repricing before you list.
Sources & notes
- California Public Law: Government Code section 66332 (legalizing unpermitted ADUs built before 2020)
- California Public Law: Government Code section 66331 (delay in enforcement)
- California Public Law: Health and Safety Code section 17980.12 (five-year delay; 2030 and 2035 dates)
- California Public Law: Government Code section 66342 (separate sale as condominiums)
- Napa County: Accessory Dwelling Units (AB 2533 legalization)
- California Department of Real Estate: Disclosures in Real Property Transactions (TDS form items, 2005 edition)
- Fannie Mae Selling Guide: B2-3-04, Special Property Eligibility Considerations (October 8, 2025)
- Fannie Mae Selling Guide: B3-3.8-02, Rental Income from the Subject Property (September 2, 2026)
Statutes were read on California Public Law because the Legislature’s site couldn’t be opened from our research environment.
Last reviewed October 2026 by Matthew Martinez.
