How Long Does It Take to Build an ADU in California? Measured Build Times for 166 Cities

Bottom line up front

The median California ADU took 346 days — about 11.4 months — from building permit to certificate of occupancy. Measured over 64,173 completed ADU projects permitted 2018–2023.
Half of projects took between 214 and 554 days. 53% were finished within 12 months and 86% within 24.
Los Angeles, the largest market, is slower than the state: a median of 407 days over 22,222 projects.
City medians range widely. Shortest among large samples: Santa Maria (193 days), Thousand Oaks (221 days), Westminster (223 days), Fountain Valley (228 days), Modesto (236 days). Longest: San Francisco (532 days), Oakland (511 days), Los Altos (491 days), Palo Alto (451 days), Alhambra (413 days).
The clock starts at the permit. Design and plan check come before it and are not in these figures.
63% of ADUs permitted in 2018–2023 have a completion on record. The rest were abandoned, are still under way, or were never reported as complete, and are not in the medians.

Fastest and slowest cities

Ranked on the median, for cities with at least 150 completed ADU projects and a completion on record for at least 50% of the ADUs they permitted in 2018–2023 (53 cities qualify). A short median is not the same as a fast building department: the mix of garage conversions and new construction, typical project size and how quickly owners start work all move it, and this data cannot separate them.

Shortest median build times

#	Jurisdiction	Median days	Middle half (days)	Done in 12 months	Completed projects	Completion on record
1	Santa Maria	193	120–324	79%	1,209	80%
2	Thousand Oaks	221	146–341	78%	183	67%
3	Westminster	223	162–335	80%	422	76%
4	Fountain Valley	228	155–336	78%	200	78%
5	Modesto	236	149–496	62%	178	77%
6	Pico Rivera	243	168–366	75%	175	71%
7	Tracy	243	200–428	72%	165	79%
8	Lakewood	254	162–387	73%	266	89%
9	Concord	255	171–430	66%	167	86%
10	Downey	255	160–363	75%	263	57%
11	Daly City	262	164–427	69%	334	91%
12	Orange	263	189–372	73%	185	73%
13	Garden Grove	268	179–430	67%	1,005	65%
14	Sacramento	268	168–378	73%	599	67%
15	Whittier	282	203–450	64%	180	64%

Longest median build times

#	Jurisdiction	Median days	Middle half (days)	Done in 12 months	Completed projects	Completion on record
1	San Francisco	532	314–800	31%	762	64%
2	Oakland	511	328–751	30%	672	50%
3	Los Altos	491	290–666	36%	179	62%
4	Palo Alto	451	288–667	39%	279	55%
5	Alhambra	413	299–560	37%	281	71%
6	Los Angeles	407	261–637	44%	22,222	75%
7	Lancaster	404	272–508	45%	302	83%
8	Fremont	393	230–630	45%	277	63%
9	Torrance	388	238–546	49%	298	73%
10	San Jose	385	242–574	46%	1,218	54%
11	Temple City	384	274–519	45%	186	73%
12	Rosemead	372	251–540	50%	336	70%
13	Salinas	369	238–612	49%	375	79%
14	Fullerton	350	238–556	52%	256	82%
15	Richmond	349	216–608	52%	202	60%

By the year the permit was issued

Build times have not shortened. For each permit year the median sits between 317 and 362 days. Permits issued in 2024 and 2025 are left out: only their fastest projects have finished, so their medians would look artificially short.

Permit issued in	Completed ADUs measured	Median days	Months
2018	5,759	350	11.5
2019	7,846	354	11.6
2020	7,839	317	10.4
2021	12,524	354	11.6
2022	15,352	362	11.9
2023	14,853	332	10.9

How we checked it: Los Angeles's own permit system

The state file is what cities report to HCD. To test whether our linking of those reports produces real build times, we compared Los Angeles — a third of the dataset — with the City's own permit system extract (LADBS, “Building Permits Issued from 2020 to Present”), which records a permit issue date and a certificate of occupancy date for each permit.

ADU permits issued 2020–2023	LADBS (city system)	HCD file, linked by us
Completed projects compared	15,961	15,123
Median days, permit to certificate	421	411
Middle half (days)	274–657	268–622
Finished within 12 months	41%	43%
Share of permits with a completion	76%	73%

Matching parcel by parcel, 99.9% of the Los Angeles projects with a parcel number in our 2020–2023 figures were found in the City's extract. For 99.4% of those, a single City permit matched both our permit date and our completion date to within 7 days. The two sources agree closely for the records tested. This check covers Los Angeles only: other cities' figures rest on the same method and on the reporting gate described below, not on a city-by-city audit.

Every jurisdiction with a publishable figure

190 jurisdictions pass the gate. “Completion on record” is the share of ADUs permitted in 2018–2023 for which the state file also holds a completion. Download this table as CSV.

Jurisdiction	Median days	Middle half (days)	Done in 12 months	Completed projects	Completion on record
Agoura Hills	276	213–513	62%	40	74%
Alameda	296	192–513	61%	114	43%
Alameda County	376	228–542	48%	130	40%
Albany	390	253–689	48%	50	47%
Alhambra	413	299–560	37%	281	71%
Anaheim	294	190–443	65%	507	77%
Antioch	180	126–377	73%	60	69%
Arcadia	476	317–665	36%	141	65%
Arcata	275	154–493	67%	75	87%
Arroyo Grande	310	215–420	60%	47	66%
Atascadero	316	234–426	66%	47	60%
Baldwin Park	328	226–464	56%	149	59%
Bell Gardens	224	155–350	75%	52	60%
Bellflower	270	190–487	66%	118	60%
Belmont	323	201–476	58%	62	59%
Berkeley	342	245–494	60%	472	79%
Brentwood	230	160–295	82%	56	64%
Buena Park	246	148–407	71%	59	72%
Burbank	168	126–228	99%	122	72%
Burlingame	475	275–698	37%	131	75%
Butte County	277	193–420	60%	76	72%
Calexico	160	101–248	97%	126	78%
Camarillo	208	138–314	86%	56	62%
Campbell	404	188–616	47%	134	69%
Carlsbad	302	182–506	60%	267	82%
Carmel	460	280–607	39%	44	56%
Carson	240	174–380	72%	61	40%
Chico	301	203–429	69%	180	89%
Chino	266	154–424	69%	65	58%
Chino Hills	299	208–482	58%	43	81%
Chula Vista	338	232–540	55%	334	61%
Citrus Heights	358	235–508	52%	69	74%
Claremont	244	162–350	77%	65	64%
Clovis	313	197–479	60%	73	80%
Concord	255	171–430	66%	167	86%
Contra Costa County	339	208–513	53%	345	71%
Coronado	376	230–675	49%	41	66%
Costa Mesa	348	209–480	51%	102	55%
Covina	252	152–390	70%	91	83%
Culver City	339	206–500	55%	267	66%
Cupertino	514	293–734	38%	87	68%
Daly City	262	164–427	69%	334	91%
Danville	344	201–566	58%	77	52%
Davis	318	216–482	66%	61	47%
Del Mar	455	312–550	38%	55	62%
Diamond Bar	331	228–484	58%	66	62%
Downey	255	160–363	75%	263	57%
Duarte	244	178–401	71%	58	77%
East Palo Alto	349	204–806	53%	73	63%
El Cajon	310	184–431	63%	138	75%
El Centro	162	100–317	81%	72	56%
El Cerrito	344	245–484	55%	77	54%
El Dorado County	270	112–485	62%	162	62%
Encinitas	284	173–524	62%	320	52%
Escondido	284	163–432	66%	184	69%
Eureka	370	198–526	49%	59	66%
Fairfax	182	101–295	79%	42	60%
Folsom	284	231–372	74%	96	64%
Fontana	324	203–504	58%	151	41%
Fountain Valley	228	155–336	78%	200	78%
Fremont	393	230–630	45%	277	63%
Fullerton	350	238–556	52%	256	82%
Garden Grove	268	179–430	67%	1,005	65%
Glendale	292	185–483	63%	962	85%
Glendora	278	158–422	62%	56	46%
Goleta	248	173–348	77%	78	84%
Grover Beach	314	149–546	60%	60	59%
Half Moon Bay	412	272–600	42%	60	71%
Hayward	342	186–540	54%	171	66%
Hemet	177	107–434	69%	49	59%
Highland	342	226–493	54%	52	81%
Kern County	315	201–488	58%	151	67%
La Canada Flintridge	352	236–495	53%	62	62%
La Habra	263	147–415	68%	78	58%
La Mesa	297	196–435	67%	202	66%
La Puente	250	168–329	80%	97	57%
Lafayette	316	254–511	54%	72	67%
Laguna Beach	316	168–536	58%	139	62%
Lakewood	254	162–387	73%	266	89%
Lancaster	404	272–508	45%	302	83%
Livermore	336	192–530	57%	202	78%
Loma Linda	119	39–208	90%	49	68%
Long Beach	295	182–473	63%	1,594	82%
Los Altos	491	290–666	36%	179	62%
Los Altos Hills	643	428–960	18%	73	55%
Los Angeles	407	261–637	44%	22,222	75%
Los Angeles County	384	249–580	47%	1,926	60%
Los Gatos	385	229–686	48%	149	70%
Marin County	442	240–728	40%	120	56%
Mendocino County	302	152–664	61%	71	63%
Menlo Park	342	267–457	57%	88	41%
Mill Valley	460	340–696	28%	47	40%
Milpitas	321	202–579	54%	89	76%
Modesto	236	149–496	62%	178	77%
Monrovia	306	224–554	61%	142	76%
Monte Sereno	554	212–770	37%	49	67%
Montebello	263	186–414	66%	56	53%
Monterey	274	164–524	61%	75	71%
Monterey County	521	258–790	38%	101	63%
Monterey Park	282	208–390	67%	76	83%
Moorpark	290	194–488	61%	59	78%
Moreno Valley	559	328–831	31%	71	56%
Morgan Hill	312	244–403	69%	48	54%
Morro Bay	364	206–616	51%	43	70%
Mountain View	354	254–595	51%	112	66%
Napa County	598	333–788	32%	60	71%
National City	392	294–512	42%	41	46%
Nevada County	371	222–497	49%	77	69%
Newark	415	276–712	43%	51	69%
Novato	321	192–512	57%	65	66%
Oakland	511	328–751	30%	672	50%
Oceanside	300	192–496	59%	368	81%
Ojai	134	57–292	81%	85	79%
Ontario	288	160–507	61%	170	52%
Orange	263	189–372	73%	185	73%
Orange County	328	218–493	58%	142	71%
Orinda	302	222–504	60%	43	52%
Oxnard	296	176–476	62%	248	72%
Pacific Grove	250	173–478	63%	86	53%
Pacifica	286	171–433	63%	78	70%
Palmdale	231	217–328	79%	111	71%
Palo Alto	451	288–667	39%	279	55%
Paramount	314	220–429	62%	64	50%
Pasadena	349	221–568	55%	237	40%
Paso Robles	218	139–394	73%	66	78%
Pico Rivera	243	168–366	75%	175	71%
Piedmont	359	203–566	51%	81	66%
Pittsburg	127	70–222	93%	43	88%
Placer County	294	204–495	59%	219	57%
Pleasant Hill	267	202–406	67%	48	48%
Pleasanton	295	206–456	62%	40	62%
Pomona	212	142–323	78%	101	44%
Rancho Cucamonga	288	189–443	65%	141	77%
Richmond	349	216–608	52%	202	60%
Riverside	313	176–508	59%	302	49%
Riverside County	185	98–302	85%	280	71%
Rosemead	372	251–540	50%	336	70%
Roseville	318	217–504	61%	69	83%
Sacramento	268	168–378	73%	599	67%
Sacramento County	273	188–379	72%	188	59%
Salinas	369	238–612	49%	375	79%
San Clemente	278	167–428	63%	82	77%
San Diego	358	230–536	52%	1,705	44%
San Diego County	364	226–547	51%	970	70%
San Fernando	164	97–278	82%	175	46%
San Francisco	532	314–800	31%	762	64%
San Joaquin County	238	164–325	85%	40	68%
San Jose	385	242–574	46%	1,218	54%
San Luis Obispo	312	186–509	60%	238	69%
San Luis Obispo County	353	257–512	52%	185	63%
San Marcos	256	184–448	62%	64	84%
San Mateo	321	190–533	54%	200	59%
San Mateo County	382	240–522	48%	111	43%
San Rafael	292	172–435	66%	88	54%
San Ramon	310	205–398	68%	44	77%
Santa Ana	301	212–441	62%	473	75%
Santa Barbara	335	195–516	56%	519	76%
Santa Clara	322	235–512	57%	233	78%
Santa Cruz	348	219–554	52%	332	79%
Santa Cruz County	378	233–574	48%	176	62%
Santa Maria	193	120–324	79%	1,209	80%
Shafter	368	307–442	47%	104	72%
Shasta County	241	102–472	64%	104	83%
Sierra Madre	294	196–456	64%	67	83%
Solana Beach	346	200–489	56%	45	69%
Soledad	182	114–295	84%	69	99%
Sonoma County	452	282–722	39%	419	67%
South Gate	240	152–371	72%	145	58%
South Pasadena	391	228–505	49%	55	42%
South San Francisco	260	191–425	70%	113	54%
Stanislaus County	190	96–384	74%	84	51%
Stanton	257	175–402	69%	84	64%
Sunnyvale	338	203–546	53%	280	88%
Temple City	384	274–519	45%	186	73%
Thousand Oaks	221	146–341	78%	183	67%
Torrance	388	238–546	49%	298	73%
Tracy	243	200–428	72%	165	79%
Upland	80	8–181	93%	69	40%
Ventura County	385	255–561	47%	88	45%
Visalia	228	160–315	83%	41	82%
Vista	277	159–518	63%	146	64%
Walnut	346	228–485	56%	88	60%
Walnut Creek	348	224–531	54%	102	84%
Watsonville	261	150–425	67%	107	71%
West Covina	258	160–356	79%	146	61%
West Hollywood	436	246–616	44%	55	67%
Westminster	223	162–335	80%	422	76%
Whittier	282	203–450	64%	180	64%
Yorba Linda	350	216–584	51%	47	60%
Yucaipa	261	143–436	65%	69	52%

Method and limits

Source. California HCD Housing Element Annual Progress Report, Table A2, October 2026 release (published 2026-10-02, downloaded 2026-10-05). Rows with unit category ADU: 281,375.

What is measured. Days from the building-permit issue date to the date HCD defines as “certificates of occupancy or other form of readiness, such as final inspection”. It includes construction, inspections, and any time the owner waits before starting or pauses mid-build. It does not include design, plan check or financing before the permit.

Linking. Table A2 holds one row per project per reporting year, so a project permitted in one year and finished in the next appears in two rows. Using only rows that carry both dates would keep mostly same-year completions and understate build time. We link rows for the same parcel (assessor parcel number, or street address where the parcel number is missing) within a jurisdiction and pair each completion date with the latest earlier permit date. 25,815 of the 64,173 measured projects were linked across years; 38,358 came from a single row. 12 ADU rows had neither a parcel number nor an address and could not be linked.

Which projects. A project is one parcel and one permit date; a permit covering several ADUs on a parcel counts once, so the counts on this page are projects rather than dwelling units. We use ADUs permitted from 2018 to 2023, completed after at least one day and within five years. Permits from 2024 onward are excluded from medians because they have not had two years to finish. 12,876 completion dates had no earlier permit date in the file (mostly permits issued before the state began collecting this data) and are not used.

Which cities. A jurisdiction is shown only with at least 40 measured projects and a completion on record for at least 40% of its 2018–2023 ADU permits. A low share usually means the jurisdiction does not report completions to the state, not that its ADUs go unfinished.

What this cannot tell you. The medians describe projects that were finished and reported. They say nothing about projects that stalled. They do not separate garage conversions from detached new construction, or 400 square feet from 1,200. HCD revises the file as cities correct their filings, so figures move slightly between releases. Treat a city's median as what has typically happened there, not as a forecast for one project.

Privacy. The state file contains street addresses and parcel numbers. We use them only to link a project's own records. Nothing on this site shows, maps or lists an individual property.

Cite this page

BackyardADU.net (2026). California ADU build times by city: building permit to certificate of occupancy (October 2026 release). Source: California HCD Annual Progress Report Table A2. https://backyardadu.net/adu-build-times/

Frequently asked questions

How long does it take to build an ADU in California?

The median is 346 days, about 11.4 months, from the building permit being issued to the certificate of occupancy. That is measured over 64,173 completed ADU projects permitted 2018–2023. The middle half of projects took between 214 and 554 days; 53% were finished within 12 months and 86% within 24.

Does that include design and permitting time?

No. The clock starts on the day the building permit is issued and stops at the certificate of occupancy or final inspection. Design, engineering and plan check happen before that; state law gives a city 60 days to decide a complete ADU application, and design commonly takes a few months. Add those to the build time.

Which California cities finish ADUs fastest?

Among cities with at least 150 completed ADU projects and good completion reporting, the shortest medians are Santa Maria (193 days), Thousand Oaks (221 days), Westminster (223 days), Fountain Valley (228 days), Modesto (236 days). Fast medians often go with a high share of garage conversions, which this data cannot separate from new construction.

Which cities take longest?

On the same basis the longest medians are San Francisco (532 days), Oakland (511 days), Los Altos (491 days), Palo Alto (451 days), Alhambra (413 days).

How long does an ADU take to build in Los Angeles?

The median is 407 days, about 13.4 months, over 22,222 completed ADU projects; 44% finished within a year. We checked the Los Angeles figures against the City's own permit system: for permits issued 2020–2023 its median is 421 days against 411 from the state file, and both dates matched the same City permit for 99.4% of the projects compared.

Why is my city not listed?

A city is shown only if at least 40 completed ADU projects can be measured and at least 40% of the ADUs it permitted in 2018–2023 have a completion on record. Many jurisdictions report permits to the state but not completions, and a figure built on a handful of projects would mislead.

Are ADUs getting faster to build?

Not measurably. For permits issued in each year from 2018 to 2023 the median build time stayed between 317 and 362 days. Permits issued in 2024 and 2025 are left out because only their fastest projects have finished so far.