Awaiting expert review. This page covers rules that vary by state and local jurisdiction. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
An ADU permit is the building permit a city or county issues to allow construction of an accessory dwelling unit, after checking the plans against local zoning standards and the building code.
It is usually one building permit with several sign-offs: planning, building, fire and utilities. Without it, the unit is unpermitted, which affects sale, insurance and rental.
Quick facts
- Issued by
- The local building department (city or county)
- Checks
- Zoning standards, building code, fire, utilities
- California review standard
- Ministerial: no hearing, no discretion 1
- California completeness deadline
- 15 business days 1
- California decision deadline
- 60 days from a complete application, where a dwelling exists on the lot 1
- Code used for design (California)
- 2025 California Residential Code, effective 1 Jan 2026 3
Key takeaways
- An ADU permit is the building permit for a second home on your lot.
- It covers zoning, the building code, fire and utilities in one review.
- Work is inspected in stages. The permit is “finaled” when the last check passes.
- In California, review is ministerial: no hearing and no judgment calls 1.
- In California, the city has 15 business days to rule on completeness and 60 days to decide a complete application 1.
- Outside California, permit steps and timelines are set locally.
Why the permit matters to you
Without a permit, an ADU is not a legal home. That can block a sale, a refinance or an insurance claim.
The permit also protects you. City inspectors check the foundation, framing, wiring and fire safety while the walls are still open.
A finaled permit is a record a lender or appraiser can trust. It shows the unit was built to code.
What a building permit is, and what makes an ADU one different
A building permit is a local government’s written permission to build, alter or demolish a structure. It confirms the plans meet the codes in force, and it schedules the inspections that check the work as it goes up. The permit is “finaled” when the last inspection passes, and the building may then be occupied.
An ADU permit is a building permit for a second, independent home on a residential lot. That adds steps a garden shed does not need: a zoning check that the unit fits the lot’s setbacks and height limit, and often an address, separate utility connections, and fire department review.
Most cities issue it as one permit with several departments signing off, though some issue separate electrical, plumbing or demolition permits alongside it. Your city’s ADU page or permit counter lists what it requires.
The typical sequence
- Check feasibility: zoning district, lot size, utilities, easements.
- Prepare drawings: site plan, floor plan, elevations, structural, energy compliance.
- Submit the application and pay plan-check fees.
- Completeness review: the city confirms the package is complete or lists what is missing.
- Plan check: reviewers return corrections until the set complies.
- Permit issued; impact or connection fees paid where they apply.
- Construction with inspections at set stages (foundation, framing, rough trades, insulation, final).
- Final inspection; the permit is finaled and the unit may be occupied.
California’s rules for ADU permit review
In California, Government Code section 66317 governs how an ADU permit application is handled 1. The application must be considered and approved ministerially, without discretionary review or a hearing.
The permitting agency must decide whether the application is complete within 15 business days, and if a single-family or multifamily dwelling already exists on the lot, approve or deny within 60 days of receiving a complete application.
If it misses the 60 days, the application is deemed approved. A denial must list the deficient items and how to fix them, and the applicant may appeal; the agency must decide the appeal within 60 business days.
The diagram shows the whole path, from submission to appeal. The step people miss is the appeal: it covers an incompleteness finding as well as a denial.
“Permitting agency” covers every entity involved in the review for which there is no substitute, including planning and building departments, utilities and special districts 2.
Section 66317 was last amended by SB 543 (Stats. 2025, ch. 520), effective 1 January 2026. It descends from Gov. Code 65852.2, which SB 477 (Stats. 2024, ch. 7) repealed and moved into Chapter 13.
These deadlines are what the statute requires; actual times vary by city, and the measured figures are on the ADU permit times by city research page.
Fees are a separate rule; see the ADU fee estimator and California ADU fees by city. Outside California, permit rules are local; see ADU laws by state.
- SubmitThe 15-business-day completeness clock starts
- Completeness noticeWithin 15 business days. No notice means the application is deemed complete
- Fix and resubmit if incompleteOnly listed items. The resubmittal gets its own completeness review
- DecisionApprove or deny within 60 days of a complete application when a home already stands on the lot
- Deemed approved or deniedA missed deadline means approval. A denial lists every deficiency and how to fix it
- AppealYou may appeal an incompleteness finding or a denial. The final written decision is due within 60 business days
California only, as amended by SB 543 (Stats. 2025, ch. 520). Business days exclude weekends and state holidays. Source: [1]
Who signs off, and on what
| Reviewer | Checks | Common correction |
|---|---|---|
| Planning / zoning | Location, size, setbacks, height, parking | Setback dimension missing on the site plan |
| Building | Structure, egress, energy, the residential code | Energy compliance forms incomplete |
| Fire | Access, separation, sprinklers where required | Fire access path not shown |
| Utilities and districts | Water, sewer, electrical service capacity | Service upgrade not shown |
Why the permit matters, and what it does not settle
What a permit gives you
- A legal second home that can be rented, insured and disclosed on sale.
- Inspected work: structure, wiring and fire safety checked by the city.
- A record lenders and appraisers can rely on.
What it does not do
- It does not guarantee a timeline beyond the statutory deadlines.
- It does not approve private restrictions such as HOA rules or recorded covenants.
- It expires if work does not start or stalls past the local limit.
If an ADU was built without a permit
- It can be a problem on sale, refinance and insurance claims.
- California has a separate process for some existing unpermitted units; see legalizing an unpermitted ADU.
- The scale of the issue is on unpermitted ADU statistics.
Types of ADU permits California must approve
| Category | Short description | Key limits named in the law |
|---|---|---|
| Conversion on a single-family lot | An ADU or junior ADU inside the house or an existing accessory structure | Expansion of up to 150 sq ft, for getting in and out only; exterior access; setbacks enough for fire safety |
| New detached on a single-family lot | A new backyard unit | Side and rear setbacks of no more than 4 ft; city may cap size at 800 sq ft and height at the state floors 5 |
| Conversions in a multifamily building | Units made from non-living space such as storage rooms, attics, basements or garages | Each unit must meet state building standards for dwellings |
| Detached on a multifamily lot | New detached units beside an apartment building | Numbers and limits set in §66323 |
Sources: [4]
Worked example: the California review clock
A hypothetical timeline to show how the state deadlines in §66317 run. Real cities vary, and correction rounds add time.
| Event | Rule | What it means |
|---|---|---|
| You submit the application | Day 0 | The completeness clock starts |
| City checks completeness | Within 15 business days 1 | You get written notice, with a list of missing items if any |
| You fix the missing items | The city may not add new items | Only items on the list can be asked for |
| City reviews the complete application | Approve or deny within 60 days 1 | If an existing home is on the lot |
| City misses the deadline | Deemed approved 1 | The law treats the application as approved |
| City denies | Full written comments in the same period 1 | A list of what is wrong and how to fix it |
If the ADU is filed with a new house, the city may wait to decide the ADU until it decides the house 1.
Where you will see the permit
- The permit card posted on site, signed at each inspection.
- The permit number on city records, which buyers and lenders check.
- Plan check letters with corrections.
- Your builder’s contract, which should say who pulls the permit.
- A sale disclosure, which asks if work was permitted.
Permit rules in other states
Every state requires permits for new homes, but the steps and deadlines are local. Some states have ADU laws with review timelines. Many do not.
Rules vary. See the state-by-state ADU law tracker and the permit times by city research.
What drives permit costs
Permit costs come in parts: plan check fees, building permit fees, and sometimes impact and utility connection fees.
They are driven by the unit’s size and value, your city’s fee schedule, and whether new utility service is needed. California has its own rules on ADU impact fees.
Use the fee estimator and the ADU fee statistics rather than a guess.
The permit compared with related approvals
| Term | What it is | When it happens |
|---|---|---|
| Building permit | Permission to build | Before work starts |
| Ministerial approval | The kind of review: rules only, no hearing | During review |
| Planning approval | Zoning sign-off | Before or during building review |
| Final inspection | The last city check | When work is done |
| Certificate of occupancy | Permission to live in it, where a city issues one | After final |
Common mistakes
- Myth A contractor’s license replaces the permit.
- Reality A license lets someone do the work. The permit is for the project and the property.
- Myth Once I have the permit, I am done with the city.
- Reality Inspections run all through construction. The permit must be finaled.
- Myth In California, the city can hold a hearing on my ADU.
- Reality State law says ADU permits are approved ministerially, without discretionary review or a hearing.
What to ask the permit counter
- What must be in a complete application?
- Do you offer pre-approved ADU plans?
- Which departments review, and are there separate trade permits?
- Which fees apply, and when are they paid?
- How long is a permit valid if work stalls?
- What inspections are required, and how do I book them?
Checklist for your project
- Run a feasibility check on your lot against the city’s objective standards, such as height and setbacks 6.
- Choose plans: custom or pre-approved.
- Assemble the full set: site plan, floor plan, elevations, structure, energy.
- Submit and log the date.
- Track the 15-business-day completeness reply in California.
- Answer corrections in one clean round.
- Pay fees and pick up the permit.
- Book each inspection. Keep the signed card.
- Get the final and keep the records.
Guides, tools and research
Questions about adu permit
Do I need a permit to build an ADU?
Yes. An ADU is a dwelling, so it needs a building permit from the city or county, with zoning and building code review and inspections during construction.
How long does an ADU permit take in California?
State law sets limits, not a typical time: 15 business days to rule on completeness, then 60 days from a complete application to approve or deny where a home already exists on the lot (Gov. Code 66317). Correction rounds add time; measured city times vary.
What is the difference between ADU permitting and a building permit?
ADU permitting is the whole process; the building permit is the document it produces. For most ADUs the zoning check happens inside the building permit review rather than as a separate approval.
What happens if a California city misses the 60-day deadline?
Under Government Code 66317(a)(3), a completed application that is not approved or denied within 60 days is deemed approved, where a dwelling already exists on the lot. The clock pauses if the applicant asks for a delay.
Can a city deny an ADU permit?
Yes, if the application fails an objective standard or the building code. In California the denial must include written comments listing what is deficient and how to fix it, and the applicant can appeal.
Who pulls the permit for an ADU, the owner or the contractor?
Either can, depending on local rules. Many owners have their contractor or designer pull it. The person who pulls it is responsible for the work meeting code. Your contract should say who does it.
How long is an ADU permit good for?
It depends on the city. Most building codes let a permit expire if work does not start or stops for a set time. Ask your building department for its rule and how to get an extension.
What documents do I need for an ADU permit?
Usually a site plan, floor plan, elevations, structural details and energy forms. Some cities also want a survey, soils report or utility letters. Your city’s ADU checklist lists what makes an application complete.
Can I use pre-approved plans to speed up my ADU permit?
Often yes. Many California cities offer pre-approved ADU plans that have already passed plan check. You still need a site plan and a permit. See the pre-approved plan finder on this site.
What happens at the final inspection?
An inspector checks the finished unit against the approved plans and code. If it passes, the permit is finaled and the unit can be lived in. If not, you get a list of items to fix and book again.
Sources
- California Legislature, Government Code §66317 (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66313, definitions (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Building Standards Commission, Codes (2025 Triennial Edition of Title 24), retrieved .
- California Legislature, Government Code §66323, ADUs a local agency must approve ministerially (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66321 (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66314 (as amended by AB 1170, Stats. 2025, ch. 67), retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Review rules were read in the current text of Government Code §§66313 and 66317 on leginfo.legislature.ca.gov on 7 October 2026; the code edition and effective date are from the Building Standards Commission. No timeline beyond the statute is stated.
Held for review (G-REV) before indexing. Education, not legal advice. Government Code §66323 (must-approve categories) and the full text of §66317 (completeness, 60-day decision, deemed approval, written denial comments) were read on 7 October 2026.
Suggest a correction. We fix errors and say what changed.