Quick answer
A building department is the city or county office that reviews construction plans against the building code, issues building permits, inspects the work as it is built and gives the final sign-off that lets a new home be lived in.
It is run by a building official. For an ADU, it is the office you deal with most, from the first plan submittal to the final inspection.
Quick facts
- Led by
- The building official, the person the code makes responsible for enforcing it 1
- Main jobs
- Plan review, permits, inspections, final approval 1
- California duty
- Every city or county building department must enforce the state building standards for dwellings 2
- Other common names
- Building and Safety; Department of Building Inspection; Building Division; Permit Center
Key takeaways
- The building department is the city office that checks how your ADU is built.
- It reviews plans, issues the permit, inspects the work and signs it off 1.
- In California, every city or county building department must enforce state building standards for homes 2.
- It is not the planning department. Planning checks where the ADU goes and how big it is.
- California law gives ADU applications a review clock that covers each permitting agency 3.
- Good habits save time: complete plans, one reply per comment, and inspections booked early.
What a building department is, in plain English
Every city or county has an office that makes sure buildings are built safely. That office is the building department.
Before you build, it reads your plans. It checks them against the building code. When the plans pass, it gives you a permit. While you build, its inspectors come out and look at the work. When the last check passes, it signs off. Then the ADU can be lived in.
The name changes from place to place. You may see “Building and Safety,” “Building Inspection” or “Permit Center.” The job is the same.
Why it matters to you
The building department holds the key to a legal ADU. Without its permit and final sign-off, the unit is not a legal home. That can block a sale, a loan or an insurance claim.
It also sets much of your pace. Plan review, corrections and inspection slots all run through this office.
It is also a free source of facts. Its counter staff can tell you what the city needs on a plan set, which forms to use and which inspections to expect.
Who you will meet there
| Role | What they do | When you meet them |
|---|---|---|
| Permit technician | Takes in applications, checks forms, collects fees, issues the permit | At intake and at issuance |
| Plan checker (plans examiner) | Reviews drawings against the code; writes correction comments | During plan check |
| Building inspector | Visits the site to check each stage of work | Throughout construction |
| Building official | Heads the office; interprets the code; decides hard cases 1 | Rarely, unless there is a dispute |
| Other reviewers | Fire, public works or utilities may review parts of the plans | During plan check, depending on the city |
How an ADU moves through the building department
- Pre-application. You or your designer ask the counter what the city needs. Many cities post an ADU checklist.
- Submittal. You file the plans and forms, often online, and pay plan-check fees.
- Completeness check. In California, a permitting agency must tell you within 15 business days if the ADU application is complete, and list what is missing if not 3.
- Plan check. Reviewers compare the plans with the code and send back corrections.
- Resubmittal. Your designer answers each comment and sends revised sheets.
- Approval and permit. The plans are approved and the permit is issued. Code law says the owner or the owner’s agent must get the permit before work starts 1.
- Inspections. Work stays open and visible until the inspector approves each stage 1.
- Final. The last inspection passes, and the permit is closed out.
Inspections you can expect on a typical new ADU
| Stage | What the inspector looks at |
|---|---|
| Foundation | Trenches, forms and steel before concrete is poured |
| Under-floor or under-slab | Pipes and ducts below the floor |
| Framing | Walls, beams, bracing and hold-downs |
| Rough plumbing, electrical, mechanical | Pipes, wires and ducts before walls close |
| Insulation | Insulation type and coverage, matched to the energy forms |
| Drywall or wallboard | Fastening, where the city inspects it |
| Final | The whole unit: smoke alarms, fixtures, exits, address, grading |
Do not cover work early
Work must stay open and visible until the inspector approves that stage 1. If drywall goes up before the rough inspection, the inspector can ask for it to come off. Ask your contractor to book each inspection before the next trade starts.
Worked example: the California completeness clock
A hypothetical example using the real deadline in Government Code 66317 3. The dates are made up.
| Step | Date | What the law says |
|---|---|---|
| ADU application received | Monday 2 March 2026 | The clock starts when the agency receives it |
| Completeness deadline | 15 business days later: Monday 23 March 2026 | The agency must give written notice that it is complete or incomplete |
| If incomplete | Notice lists missing items and how to fix them | The list must come with the notice |
| If the agency misses the deadline | The application is deemed complete | The law treats it as complete |
| Decision on a complete application | Within 60 days, where a dwelling already exists on the lot | The agency must approve or deny |
Count business days only: no weekends, and skip any city holiday in between. Real review times vary by city; see ADU permit times by city for measured figures.
Where you will see the building department
- On your permit card, with the permit number and inspection list.
- On plan-check correction letters, signed by a plan checker.
- On stamped approved plans that must stay on site.
- On inspection results, posted online or on the job card.
- In the property’s permit history, which buyers and appraisers check.
- On the city’s fee receipts for plan check and permit.
California’s rules, then other states
In California, state law tells the building department of every city or county to enforce the state building standards for homes and apartments in its area 2. Those standards are Title 24. The 2025 edition took effect on 1 January 2026 5.
The code edition is locked by your application date. Only standards in effect locally when you submit apply to that permit 4.
For ADUs, Government Code 66317 sets the review rules. An ADU permit application must be approved ministerially, without a hearing. The agency has 15 business days to decide if it is complete.
It must approve or deny a complete application within 60 days where a home already exists on the lot 3. For more on what “ministerial” means, see ministerial approval.
Outside California, building departments run under state and local law. Some states let counties choose whether to enforce a code at all in rural areas. Review times and inspection lists differ widely. See ADU laws by state.
The three figures below are the California dates and deadlines to track on your own calendar from the day you apply.
- 15 business daysTo tell you whether an ADU application is completeGov. Code 66317 3
- 60 daysTo approve or deny a complete ADU application where a home already exists on the lotGov. Code 66317 3
- 1 Jan 2026The 2025 Title 24 standards took effect; your application date locks the editionBuilding Standards Commission 5
Building department costs and what drives them
No dollar figures here; each city sets its own fees. These are the drivers.
- Plan-check fees, often based on the project’s valuation or size.
- Permit fees, also often tied to valuation.
- Re-inspection fees when work is not ready or fails.
- Fees for extra review rounds in some cities.
- Separate trade permits in cities that split them out.
- Other agencies’ fees, such as school or utility fees, collected by or alongside the department.
Check fees for your city
- ADU fee estimatorEstimate permit and impact fees
- California ADU fees by cityPublished fee schedules compared
Working with the building department: benefits and limits
What it does well
- Inspectors catch mistakes while walls are still open.
- A finaled permit gives you a clean record for sale and finance.
- Counter staff answer code questions at no cost in many cities.
- In California, ADU reviews have legal deadlines 3.
Where it falls short
- Review and inspection waits can slow a project.
- Different reviewers may read the code differently.
- Each round of corrections costs design time.
- The department checks code minimums, not workmanship quality.
Building department compared with related offices
| Office | Checks | ADU example |
|---|---|---|
| Building department | How it is built: structure, fire, exits, systems | Footing size, egress window, smoke alarms |
| Planning department | Where it goes and how big | Setbacks, height, size limits |
| Fire department | Fire access and protection | Access path, hydrant distance |
| Public works | Work in the street and sewers | A new sewer lateral or driveway |
| Utility | Power, water, gas service | A new meter or bigger service |
| Permit expediter | Not a city office; a hired helper | Prepares and tracks your submittal |
Common misreadings
- Myth “The building department approves the location of my ADU.”
- Reality Location, size and setbacks are usually a planning check. The building department checks construction.
- Myth “Once the permit is issued, the city is done.”
- Reality Inspections follow at each stage, and the permit is not closed until the final passes.
- Myth “The inspector will tell me how to fix everything.”
- Reality Inspectors cite what failed. Your designer and contractor decide how to fix it.
- Myth “Passing inspection means the work is good quality.”
- Reality It means the work met code minimums at the time of the visit.
- Myth “California cities can take as long as they want on an ADU.”
- Reality State law sets a completeness deadline and a decision deadline 3.
What to ask the building department
- Do you have an ADU submittal checklist?
- Which code editions are you enforcing now?
- Do you offer a pre-application meeting?
- How are plan-check fees calculated here?
- Do you accept pre-approved ADU plans? See pre-approved plan finder.
- Which inspections are on the permit card for a new ADU?
- How do I book an inspection, and how far ahead?
- How long is a permit valid, and how do I extend it?
Checklist: working smoothly with the building department
- Look up the department’s ADU page and checklist.
- Confirm zoning first with planning, so building review is not wasted.
- Submit a complete set: plans, structural, energy, forms.
- Log the submittal date to track any state deadline.
- Answer every correction in one numbered response.
- Keep approved plans and the permit card on site.
- Book each inspection when work is truly ready.
- Get the final sign-off in writing and keep it.
Related guides, tools and research
- ADU permits guideThe whole permit path
- California permit data directoryWhere cities publish permit data
- ADU timeline plannerMap review and build time
- ADU plansWhat goes into the plan set
Questions about building department
What does a building department do?
It reviews construction plans against the building code, issues permits, inspects work during construction and gives the final approval. For an ADU, it is the office that confirms the unit is built safely. Planning, fire and utilities may review other parts.
Is the building department the same as the planning department?
No. Planning checks where a building can go and how big it can be under zoning. The building department checks how it is built under the building code. Many cities put both in one permit center, but the reviews are separate.
What is a building official?
The building official heads the building department. The model codes make this person responsible for enforcing the code and interpreting it in hard cases. Day-to-day work is done by plan checkers and inspectors.
How long does a building department take to review ADU plans in California?
State law gives a permitting agency 15 business days to say whether an ADU application is complete. It must approve or deny a complete application within 60 days where a home already exists on the lot. Real times vary by city.
Can I talk to the building department before I submit?
Many departments offer counter help or pre-application meetings. Ask what the city needs for an ADU and which code editions it uses. This often prevents a round of corrections.
What happens at a building inspection?
An inspector visits the site and checks one stage of work against the approved plans and the code. If it passes, you move on. If not, you get a correction notice, fix the work and book a re-inspection.
How do I find a property’s permit history?
Ask the building department that serves the property. Many post permit records online by address. Others need a records request. Permit history shows whether past work, like an existing ADU, was permitted and finaled.
Can the building department deny an ADU?
It can deny or hold plans that do not meet the code until they are fixed. In California, an ADU application that meets the rules must be approved ministerially. A denial must come with comments on what is wrong.
Who schedules inspections, the owner or the contractor?
Usually whoever holds the permit, often the contractor. Owner-builders schedule their own. Each city has its own booking method, often online or by phone.
What does finaled mean?
A permit is finaled when the last inspection passes and the building department closes it. For a new ADU, this is the record that it was built legally. Keep a copy.
Sources
- International Code Council, 2024 International Building Code, Chapter 1 (sections 103.1 enforcement agency, 105.1 permits required, 110.1 inspections), retrieved .
- California Legislature, Health and Safety Code §17960 (building department enforcement), retrieved .
- California Legislature, Government Code §66317 (ADU application completeness and decision deadlines; as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Health and Safety Code §18938.5 (standards in effect at application), retrieved .
- California Building Standards Commission, Codes (2025 Title 24, effective 1 January 2026), 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: Roles and duties read in ICC 2024 IBC Chapter 1; California statutes read on leginfo.legislature.ca.gov; Title 24 edition read on the Building Standards Commission site, all on 2026-10-08.
Suggest a correction. We fix errors and say what changed.