About ADU Build Works — Our Rules Pack and Permit-Record Methodology
Every verdict on this site cites a rule and a checked date, and every permit figure comes from an official ledger. This page shows how both are built, what they cannot tell you, and when they are re-checked.
The short answer
A 75-rule pack checked against primary sources, plus 752 official permit records — with every gap stated
- Rules: 75 rules for California, unincorporated Marin County, San Rafael, Mill Valley and San Francisco. 65 are verified against primary sources; 3 come from chaptered bill text awaiting a re-pull on Dec 28, 2026; 5 are shown only with their attribution; 2 are held back because no source supports them.
- Permit records: 752 ADU permits from three official ledgers — City of Mill Valley issuance reports, the County of Marin open-data permit set, and San Francisco’s DBI open data — pulled Nov 4, 2026.
- The standing caveat: a declared permit valuation is recorded for fee calculation. It is not what a project finally cost.
Rules pack compiled Nov 4, 2026. Permit pull dated Nov 4, 2026. Next scheduled re-checks: Dec 28, 2026 (state law ahead of Jan 1, 2027) and Jan 2, 2027 (fee-waiver expiry).
Who runs this site
A matching service, not a builder
ADU Build Works is an ADU research and matching service for Marin County and San Francisco. It is not a builder, a licensed contractor, a law firm or a public agency, and it does not do construction. The service is run by email: there is no public phone line, and every question sent to the address in the footer gets a written answer.
The contractor roster is enrolling and no contractor is signed yet. When a seat fills, How it works will say who the roster covers and how they were screened, and homeowners in line are told the contractor’s name before any introduction.
The rules pack
How a rule earns its place in a verdict
Each rule records the statement, its threshold, its source, the date it was checked and one of four confidence labels. The checker only shows a rule in the way its label allows.
| Label | What it means | Rules |
|---|---|---|
| Primary-verified | The primary source (statute, municipal code, official programme page or fee schedule) was opened and read | 65 |
| Verified via chaptered text | 2026 bills confirmed from chaptered text and legal alerts while the state’s legislative site blocked automated reads; re-pulled at the Dec 28, 2026 gate | 3 |
| Attributed | Shown only with its source named and a confirm-with-the-agency instruction | 5 |
| Not verified — held back | Never shown as fact; the verdict says the point is unconfirmed instead | 2 |
Where a town’s own ordinance has not been verified for the checker, the verdict says it rests on the California state floor and labels every rule as a state rule. Another town’s caps, fees or review triggers are never swapped in.
The permit records
Three official ledgers, read the same careful way
| Ledger | Window | ADU permits | Standalone | What it does not carry |
|---|---|---|---|---|
| City of Mill Valley monthly “Permits Issued with Fees and Values” reports | Sep 2025 – Sep 2026 (11 of 13 monthly reports; Nov 2025 and Jul 2026 could not be located) | 27 | 12 | Square footage for half the records |
| County of Marin open data, building permits (county-issued only) | Issued 2023 – Nov 2026 | 256 | 189 | Fees, status, square footage; its locality field is a postal name, not the permitting jurisdiction |
| San Francisco DBI building permits flagged as ADUs | Filed 2023 – Nov 2026 | 469 | 314 | Fees; costs are applicant estimates at filing |
- Standalone versus mixed. A permit that bundles an ADU with a remodel or a new main house is flagged mixed and kept out of every ADU median. Mixed permits run several times higher, which is exactly why they are excluded.
- Timing. The same records give the time from application to issuance. For standalone ADUs the median was 186 days in Mill Valley, 205 days in unincorporated Marin and 216 days in San Francisco (permits issued by the pull date). The state’s 60-day clock runs only from a complete application, so real waits run longer.
- Privacy. No owner names or street addresses are published. Examples are shown at town or district level with the permit number, so anyone can trace them to the official source.
- San Rafael. The city publishes no bulk per-permit data, so its guide carries no permit evidence and no borrowed numbers.
Cost figures
Planning ranges are labelled as planning ranges
The Marin cost bands are dated planning ranges, published as estimates and never validated against permit valuations, because declared valuations measure something different. San Francisco verdicts never show a Marin figure; where no San Francisco band is sourced, none is shown.
Check the method on your own lot
Run the checker and read the sources it cites
Check my lot
FREE · FAST VERDICTStep 1 of 2 — your address and one tap on what you want to build. That is enough for a first verdict; sharpen it afterwards only if you want to.
Every type, answered — not just the one you picked
True cost — the planning band, the fees on record, and what the band leaves out
Not in the band — budget these separately; no honest source lets us put a number on them for your lot, so none is invented:
How long until someone can move in?
Dates that change this decision
What the permit record shows
What would change this answer
Lay your quotes side by side
Print this sheet and write each contractor's figures in a column. Every row is something a comparable bid has to state; a blank in a quote is a question for that contractor, not a saving. The first column is your brief, filled from your answers.
| Line every quote must state | Your brief | Quote A | Quote B | Quote C |
|---|
Check each contractor's licence number on the Contractors State License Board's public lookup (cslb.ca.gov) before you compare prices. Figures in your brief are the rule caps and planning estimates shown above, not bids.
Make your verdict more exact (optional)
Skip these — save my brief now ↓San Francisco screening — two questions that decide an SF project
In San Francisco, space a tenant uses can be a protected “housing service” — it changes what’s allowed, so we ask now, not later. Why this matters →
Stored and confirmed
Anything wrong in that summary? Email us at adu@adubuildworks.com and we'll correct the record.
We already have this brief from you
If something changed — a different project, a new budget — email us at adu@adubuildworks.com and we'll update the record. Your verdict itself is above, and it stays yours.
That didn't go through — nothing was sent
Your verdict is right here on this page, and it stays yours. Prefer to do this by email? Write to us at adu@adubuildworks.com with your address and what you'd like to build, and we'll set it up with you — no dead end.