How Long Does an ADU Permit Take in Marin County?

The county record

189 permits, one table

Unincorporated Marin covers the places outside city limits — Kentfield, Greenbrae, Tam Valley and Strawberry (which carry Mill Valley addresses), Lucas Valley and Santa Venetia (San Rafael addresses), and West Marin from Stinson Beach to Tomales. For every standalone ADU permit the county issued from January 2023 to early November 2026, we counted the days from application to issuance.

Thirty-one took longer than a year. Ten took longer than two. The quickest was issued in 7 days; the slowest took 1,469.

One limit you should know about. The county's file lists permits that were issued. It does not list applications that are still open or were abandoned, so this table describes the projects that made it through — the true picture for everyone who applied is somewhat slower than this.

The measure also includes both sides' time: the county's review, and the weeks an applicant's designer spent answering comments. The record does not split them.

By project type

Which kind of ADU got its permit fastest?

The order is roughly what you would expect — work inside an existing structure moved a little faster than a new building — but the gap is about six weeks, not six months. Choosing a conversion over a detached unit is a sound way to cut cost. On this record it is only a modest way to cut the permit wait.

The "middle half" column matters more than the median. A garage conversion at the slow end of its middle half (242 days) took longer than a detached ADU at the fast end of its own (141 days). Your lot and your application decide more than your ADU type does.

By filing year

The trend looks good. Read it carefully.

Two things are going on, and only one of them is good news.

The illusion. Our file starts with permits issued in January 2023. An application from 2021 could only be in it if it took more than a year — so the 2021 and 2022 rows are slow by construction. At the other end, a 2026 application can only be in it if it was issued fast; the slow ones are still open. Both ends of the table are bent.

The part that may be real. The 2023 and 2024 rows are the least distorted, and they sit at 230 and 204 days. That is the fairest reading of "normal" for the county: roughly seven months at the median. Whether 2025 and 2026 are truly faster will only be clear once their slow permits are issued and counted.

Mill Valley

Inside city limits: 186 days, on a small sample

The City of Mill Valley publishes a monthly list of permits issued. In the eleven monthly reports available from September 2025 to September 2026, we found 12 standalone ADU permits.

• Median, application to issuance: 186 days. Middle half: 130 to 259 days.
• Quickest 62 days; slowest 710. Five of the 12 were issued within six months, and 11 of the 12 within a year.
• By type: six detached ADUs at a median of about 186 days, and four conversions at 174.

Twelve permits is a small sample. It is enough to say that Mill Valley's wait has looked like the county's — it is not enough to rank the two.

Mill Valley has one fork worth knowing before you design. An ADU that meets the city's objective standards is approved by staff. One that does not — the city's own example is a 1,096 sq ft unit at 19 ft 11 in — goes to discretionary review and a public hearing. And a conversion that needs more than 50 cubic yards of excavation, or a raised roof, can lose its conversion status. Details: Mill Valley ADU rules.

San Rafael, Novato and the other towns

San Rafael publishes no bulk per-permit data, so there is no San Rafael median here. We have not yet measured Novato, Tiburon, Larkspur or the other towns either. Where we have no record we say so; we do not stretch the county's number over a town it does not cover. What is the same everywhere is the state rule below.

The 60-day rule

What state law guarantees — and what it leaves out

The guarantee. Every Marin jurisdiction must approve or deny a complete ADU application within 60 days, by staff, with no hearing — or within 30 days if you use a plan the jurisdiction has already pre-approved. No Marin jurisdiction publishes a faster local promise.

The catch. The 60 days run from a complete application, and stop at the decision. Getting to "complete," and getting from "approved" to "issued," sit outside the clock.

The 2026 fix. Under SB 543, since January 1, 2026 a jurisdiction has 15 business days to rule your application complete or give you a list of what is missing, and another 15 business days for each resubmittal. Silence means the application is deemed complete — not approved — and the 60 days begin.

Pre-approved plans. State law cuts the decision to 30 days for a detached ADU on a pre-approved plan. As of November 4, 2026, Marin County had not posted a catalogue of its own pre-approved plans; the programme was still in development. ADU Marin (adumarin.org), the free service every Marin jurisdiction points owners to, is the place to ask what is currently accepted where.

What slows a Marin permit

Six things that pull a project out of the fast lane

The permit record does not give reasons. The county's code and decisions do tell us where a simple ADU stops being simple.

1. Planned districts, ridgelines, stream areas and the coast. In unincorporated Marin, a state-exempt ADU is itself approved without design review. But in a Planned (P) district, on a ridgeline, in a Stream Conservation Area or in the coastal zone, other work proposed alongside it can be pulled into Design Review even when the ADU itself is not.
2. The coastal zone. A coastal permit is still required. Since October 2025, state law gives the local agency 60 days to decide a complete coastal permit application for an ADU, and the local decision can no longer be appealed to the Coastal Commission. That shortens the tail; it does not remove the permit.
3. Size above the guaranteed envelope. A detached ADU up to 800 sq ft, 16 ft high, 4 ft from side and rear lines is guaranteed by state law. Past that, you are relying on local standards, and in some towns a hearing.
4. Water. In the Marin Water district, a qualifying ADU needs no new water service — but the district reviews a Project Information Form first, which it says takes 10 to 14 business days. File it early, in parallel.
5. Septic. On a septic lot, whether the system can serve another unit is a separate question with its own review. Many West Marin lots are on septic, so ask this first there.
6. Incomplete first submittals. The only delay entirely in your team's hands.

The fee-waiver clock

If you are racing December 31, 2026

In unincorporated Marin, the county waives up to $2,500 in fees per ADU and $1,500 per junior ADU, on a programme that runs through December 31, 2026.

What must happen by that date is unconfirmed. The county's published programme does not say whether the qualifying event is an application, an issued permit, or something else. Confirm it with Marin County's Community Development Agency before you rely on it.

Here is why the answer matters. If the trigger is an application on file, you have until late December. If it is an issued permit, the record is blunt: 3 of 189 county ADU permits were issued within 60 days of applying. Plan for the stricter reading until the county tells you otherwise. Full detail: Marin ADU fee waiver.

After the permit

The build: 440 days in the county, 502 in Mill Valley

State housing records track a second span — from the day a permit is issued to the day the unit is recorded complete. For ADUs permitted from 2018 to 2023:

These come from different projects and different years than the permit waits above, so we never add the two together. Side by side, they say this much: in Marin the build has typically taken about twice as long as the permit.

Ready to start

If you plan to apply this winter

1. Check the lot first. Town or unincorporated, sewer or septic, slope, fire zone, coastal zone. The lot checker below does it in about a minute.
2. Design to the guaranteed envelope if speed matters more than size.
3. Ask whether a pre-approved plan is accepted in your jurisdiction. Where one is, the law's 30-day decision applies.
4. File the water form and any septic review in parallel, not after planning approval.
5. Submit a complete application and ask for the completeness ruling in writing. The 15-business-day answer is your right since 2026.
6. Line up your builder during review. Bids take weeks; get them on the same drawings while the permit is pending. Start with how to vet a Marin ADU builder and the quote comparison worksheet.

Questions, answered

Marin ADU permit timing: quick answers

Keep going

Related Marin guides

Check your lot

Find out what your lot adds to the clock

Type your address and tap twice. You get a plain-language verdict on screen — what your lot can likely take, and the flags that slow a permit — before we ask for any contact details. If you choose to save your brief, we store it and tell you so. No builders are signed to our roster yet, so no quotes are available today and no builder will contact you.