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San Mateo County · ADU permit data · Updated 2026-10-20

How long does an ADU permit take in San Mateo?

78permits a year ADU building permits, 2023–2025 average

Bay Area
6.0 mo
Status
Too few
Rank
unranked

We cannot publish a reliable wait time for San Mateo. Fewer than 10 ADUs here could be matched from application to permit in 2023–2025.

State limit
60 days
Bay Area
6.0 mo
months
Months from application to ADU permit, 2023–2025, drawn to one scale. The state's 60-day clock starts once an application is complete.
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Permit wait

All 52 ranked cities

Months from ADU application to building permit

Bay Area figures for reference. Fewer than 10 ADUs here could be matched from application to permit in 2023–2025.

Source: California HCD Annual Progress Reports, filed by the City of San Mateo

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Fast quarter, median and slow quarter, in months

San Mateo County

Bay Area 3.8–10.5 mo

Median Fast quarter to slow quarter

Median wait

  • San Mateo County 7.0 mo
  • Bay Area 6.0 mo
  • Atherton fastest nearby 3.4 mo
  • Half Moon Bay slowest nearby 15.9 mo

Median wait in the 52 ranked cities

Other ranked cities Bay Area 6.0

Bay Area

6.0months

median of 5,578 matched Bay Area permits, 2023–2025

Permits issued

235 ADU permits, 2023–2025

ADU building permits issued and ADUs finished, by year

Source: units by calendar year, as reported by the City of San Mateo to California HCD

San Mateo, units per year

0 45 90 2018: 8 Permits issued2019: 46 Permits issued2020: 59 Permits issued2021: 72 Permits issued2022: 80 Permits issued2023: 79 Permits issued2024: 66 Permits issued2025: 90 Permits issued 2018: 6 ADUs completed2019: 21 ADUs completed2020: 35 ADUs completed2021: 52 ADUs completed2022: 51 ADUs completed2023: 64 ADUs completed2024: 42 ADUs completed2025: 68 ADUs completed 90 Permits issued 68 ADUs completed 20182020202220242025

ADU permits a year, 2023–2025 average

ADU permits a year per 1,000 houses, 109 places

San Mateo 4.2

San Mateo Other Bay Area places

San Mateo

78a year

ADU permits, 2023–2025 average

Share of new homes that are ADUs

Of every home San Mateo permitted in 2023–2025, this share was an ADU.

Source: HCD Annual Progress Reports, 2023–2025

San Mateo

43%

ADU permits per 1,000 houses

Permits a year for every 1,000 detached houses, so small and large cities can be compared.

Source: HCD Annual Progress Reports; DOF housing estimates

San Mateo

4.2

rank 21 of 92

Change since 2019–2021

Yearly ADU permits in 2023–2025, up 33% from 2019–2021.

Source: HCD Annual Progress Reports

San Mateo

+33%

Build time

151 finished ADUs

Building permit to finished ADU

Median time from building permit to certificate of occupancy for ADUs finished in 2023–2025. Add it to the permit wait for a full timeline.

Source: HCD Annual Progress Reports, 2023–2025

San Mateo

12.3months

median of 151

Slow quarter of builds took longer than

One ADU in four took longer than this to reach a certificate of occupancy after the permit.

Source: HCD Annual Progress Reports, 2023–2025, 75th percentile

San Mateo

16.9months

San Mateo County

21 cities and areas · all cities
Months from ADU application to building permit

Median Fast quarter to slow quarter Bay Area median, 6.0 months Number is the rank out of 52 cities

06121824
median
  1. 8Atherton
    3.4
  2. 21Hillsborough
    5.3
  3. 27Belmont
    6.0
  4. 32San Carlos
    6.3
  5. 35Unincorporated San Mateo County
    7.0
  6. 47East Palo Alto
    8.6
  7. 49Burlingame
    9.1
  8. 52Half Moon Bay
    15.9

Every page in San Mateo County: median wait where we can measure it, otherwise ADU permits a year

Planning an ADU in San Mateo

  1. 1 After the permit, ADUs here took a median of 12.3 months to reach a certificate of occupancy (Bay Area: 13.0).
  2. 2 San Mateo permits about 78 ADUs a year, up 33% from 2019–2021. Local designers and builders have recent examples to show you; ask for permitted ADUs in San Mateo, not elsewhere.
  3. 3 The part of the wait you control is the first submission. Complete drawings, a site plan that matches the survey, and answers to the city's ADU checklist cut down on correction rounds.
  4. Read next: why home plans get sent back · permit drawings vs. full plans · architect fee calculator

Timeline tool

When would your permit come through?

Pick a start date and see the fast, likely and slow dates for San Mateo, from the numbers on this page.

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Next step

Not sure who to call first?

Answer a few questions about your lot and your plans. We point you to the right kind of help for an ADU in San Mateo: an architect, a permit-drawing team, or a design-build firm. About two minutes, no call list.

Find the right first call

Start with the city's own rules: ADU information and resources.

Sheet
C-180
Drawing
ADU permit record, San Mateo
Source
California HCD Annual Progress Reports, filed by the City of San Mateo
Date
2026-10-20
Scale
Not to scale

Source: Bay Area ADU Permit Clock 2026, our analysis of the California HCD Housing Element Annual Progress Reports (data.ca.gov) filed by the City of San Mateo, and DOF housing estimates. Wait times are matched on parcel number and include applicant revision time. The 60-day rule is in Government Code section 66317. How we measured it · See all 109 jurisdictions

Common questions

How long does it take to get an ADU permit in San Mateo?

There are not enough comparable records to give a reliable number for San Mateo. Across the Bay Area the median was 6.0 months.

How many ADUs does San Mateo approve?

San Mateo issued 235 ADU building permits in 2023–2025, about 78 a year. ADUs were 43% of all new homes permitted there.

How long does it take to build an ADU in San Mateo?

The median time from building permit to certificate of occupancy was 12.3 months for ADUs completed in 2023–2025.