The rule in 6 cities, with their permit counts
Rules from each city's own page, read 23 October 2026. Counts are ADU permits in the city's file over three years to September 2026; "usual days" is the typical time from issue to final inspection.
| City | What the page says | ADU permits | Usual filed value | Usual days to final |
|---|---|---|---|---|
| Austin, TX | Its accessory-structure exemption applies only if the building "does not create a dwelling, contains no plumbing" | 465 | — | 405 |
| Denver, CO | "All new ADUs need zoning, building, and sewer use and drainage permits (SUDP)", plus trade permits | 262 | $137,144 | — |
| San Diego, CA | A building permit for every ADU; an ADU "Is 1,200 square feet in size or less", at least 150 | 1,278 | $127,372 | 442 |
| San Diego County (unincorporated) | The shed exemption covers only structures "used as non-habitable space" up to 120 sq ft | 334 | $128,106 | 351 |
| Sacramento County (unincorporated) | "New homes, buildings, Accessory Dwelling Units (ADU)" need a permit | 207 | $133,039 | 254 |
| Anaheim, CA | "Accessory structures" and "Additions and remodels" need a permit; ADUs are not named separately | 330 | $100,000 | 307 |
Three more, without ADU counts in our file: Bellevue requires approval for an interior ADU ("This review takes several weeks") plus "a building permit and plan review" for the changes. Citrus Heights and Pikes Peak Regional (Colorado Springs) list garage conversion as permit work.
What an ADU permit involves
Several permits, not one. Denver's list is the fullest: zoning, building and sewer use and drainage permits, which can be reviewed together if everything is uploaded at once, then electrical, plumbing, mechanical and roofing trade permits, which "in most cases, are issued online as quick permits". Denver also applies its construction-waste ordinance to new construction over 500 square feet: "Building construction permits will not be issued until an initial waste diversion plan is approved and a refundable performance security deposit is paid." In a historic district Denver wants a certificate of appropriateness first.
San Diego's IB 400 adds setbacks: an ADU structure over 16 feet tall needs at least 4 feet from the interior side and rear lot lines. Zoning, not the building code, decides whether an ADU is allowed at all; Denver allows them "in all zone districts that allow new single unit dwellings".
What happens if you skip it
- Seattle: a stop work order and fines of "up to $500 per day" for building without a permit.
- Colorado Springs area: Pikes Peak Regional files a "Certificate of Alleged Non-compliance" against the property with the county Clerk and Recorder.
An unpermitted unit can sometimes be legalized after the fact; can an unpermitted ADU be legalized covers how.
Who pulls it
The general contractor or ADU builder, with a designer for the plans. Owners can act as owner-builder in some places, but an ADU is a house: plan review, utilities and every trade. What is an ADU covers the types, and ADU vs addition the trade-off with building onto the main house.
How long it takes
The usual ADU permit closed in 254 days in Sacramento County and 307 in Anaheim, against 351 in San Diego County, 405 in Austin and 442 in San Diego. 94.0% of Anaheim's ADU permits a year or more old reached a final, against 75.1% of San Diego's. Tie the last payment to the final inspection.
Check it in five minutes
- Look up your zone on the city's map and whether it allows an ADU.
- Find the city's ADU bulletin (San Diego's is IB 400) for size and setback limits.
- Check a builder's past ADU permits for finals before signing. San Diego County prices are in ADU cost in San Diego County.
See every San Diego ADU builder by permits filed and finished →
What this does not tell you
We read nine departments' rules; state ADU laws, utility connection fees and HOA rules are separate. Our days run from issue to final and leave out plan review before issue. An ADU filed as an addition or new home is not in these counts.
How we know this
Rules are quoted from the pages under Sources, read 23 October 2026. Permit counts, filed values, usual days to final and finished shares come from each city's permit file over the three years ending September 2026. "Usual days" is the median from issue to final inspection; "reached a final" counts permits a year or more old.
Numbers come from City of Austin issued construction permits; City and County of Denver residential construction and demolition permits; City of San Diego Development Services approvals; San Diego County Planning & Development Services building permits on homes in the unincorporated county (the County's open-data permit, contractor and status-history files); Sacramento County building permits on single-family, duplex and townhouse homes in the unincorporated county (the County's Accela permit layer); City of Anaheim Accela building permits on single-family homes and ADUs, data through October 17, 2026. Nobody paid to be on this page and nobody can.
Questions
- Do I need a permit to convert a garage into an ADU?
Yes. Citrus Heights answers YES for 'GARAGE CONVERSION', Sacramento County and Pikes Peak Regional (Colorado Springs) both list garage conversion as permit work, and Bellevue requires 'A permit with plan review' for converting a garage into living space.
- Can a shed or tiny house be an ADU without a permit?
No. The shed exemptions are written for storage: Austin's covers a structure that 'does not create a dwelling, contains no plumbing', and San Diego County's covers only structures 'used as non-habitable space' up to 120 square feet. Once someone lives in it, it is a dwelling and needs a permit.
- How big can an ADU be?
It depends on the city. San Diego defines an ADU as '1,200 square feet in size or less' with a minimum of 150 square feet, and allows one ADU up to 800 square feet even where floor-area limits would otherwise block it. Check your own city's ADU rules; the building permit sits on top of them.
- How long does an ADU permit take?
The usual ADU permit reached its final inspection in 254 days in Sacramento County, 307 in Anaheim and 405 in Austin, against 442 in San Diego. That clock starts at issue, after plan review.
- What does a permitted ADU cost?
The usual filed value on an ADU permit was $137,144 in Denver, $133,039 in Sacramento County, $127,372 in San Diego and $100,000 in Anaheim. Filed values are what the contractor wrote on the application and may leave out site work and fees.
Build your own list
Every firm with that kind of permit on record. Pick what you value. The list moves.
Related guides
- Can an unpermitted ADU be legalized? California's AB 2533 rule, and what it costs and takes
- ADU construction cost in 2026: what ADU permits were filed at in 12 cities
- Do I need a permit for a pool? Yes for in-ground: the rule in 13 cities, and how long they take
- What is an ADU? ADU vs DADU vs JADU, California's rules, and what ADU permits show
- Raleigh ADU rules: sizes, setbacks, the Not For Rent rule for owner-builders, and what ADU permits were filed at
- San Diego ADU Home Density Bonus Program after the 2025 changes: where it still applies, the caps, and hiring a builder
For one city
- Work Exempt from Building Permits — City of Austin Development Services (accessed 2026-10-23)
- Permitting an Accessory Dwelling Unit (ADU) — City and County of Denver CPD (accessed 2026-10-23)
- Quick Permits — City and County of Denver CPD (accessed 2026-10-23)
- Information Bulletin 400: ADU/JADU (August 2025) — City of San Diego Development Services (accessed 2026-10-23)
- When is a Permit Required? — City of San Diego Development Services (accessed 2026-10-23)
- PDS 110 Building Permit Requirements per Adoptive Ordinance (rev. 01/01/2026) — County of San Diego (accessed 2026-10-23)
- Frequently Asked Questions — Sacramento County Building Permits and Inspection (accessed 2026-10-23)
- When is a Building Permit Required? — City of Anaheim, CA (accessed 2026-10-23)
- Work requiring permits — City of Bellevue, WA (accessed 2026-10-23)
- Projects Requiring a Building Permit (CHB0600, rev. 08/23) — City of Citrus Heights, CA (accessed 2026-10-23)
- Homeowner Permits — Pikes Peak Regional Building Department (accessed 2026-10-23)
- Construction Without a Permit — Seattle SDCI (accessed 2026-10-23)