ADU Specialists — Marin First
We're ADU specialists — it's all we do. Tell us your address and what you want to build. You get a straight, plain-language answer for your lot, what it should cost, and — with your separate OK — your brief goes to the matched roster for your territory, so you can receive up to 2–3 comparable quotes and choose. No homework. No 40-page guide to read first.
Marin planning ranges (estimates, not bids) from ADU Build Works research, Nov 2026 — the full Marin cost guide shows what drives them, and your verdict prices your lot specifically. A builder's site visit produces the exact number.
Roster status, plainly: our founding roster is enrolling and no builders are listed yet. Your verdict and plan are yours in full either way — and checked homeowners are first in line for matching when their territory's seats fill.
Step 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.
Not in the band — budget these separately; no honest source lets us put a number on them for your lot, so none is invented:
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.
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 →
Anything wrong in that summary? Email us at [email protected] and we'll correct the record.
If something changed — a different project, a new budget — email us at [email protected] and we'll update the record. Your verdict itself is above, and it stays yours.
Your verdict is right here on this page, and it stays yours. Prefer to do this by email? Write to us at [email protected] with your address and what you'd like to build, and we'll set it up with you — no dead end.
Market figures are estimates from the ADU Build Works demand audit, Nov 2026 — the feasible-lot count is a modelled estimate, and the permit pace is a floor range from reported Marin counts, not a promise about any single lot. Cost figures on this page are planning ranges (estimates, not bids); every guide on this site carries that town's real fees and rules, or it doesn't ship.
DEC 31, 2026
Unincorporated Marin County's ADU fee waivers — up to $2,500 per ADU, $1,500 per JADU, more if deed-restricted — run through Dec 31, 2026. The qualifying event that must happen by that date is unconfirmed in the county's published programme — confirm with Marin County CDA before relying on the deadline. Who qualifies, and how to apply →
JAN 1, 2027
California's newest law (AB 956) takes effect: two detached ADUs on one single-family lot. Homeowners who plan now — including the two-unit option in the checker above — are first in line when it lands. What it means in San Francisco →
Costs, answered straight
Guide sites bury cost in page four. We put it on the homepage, because a homeowner who can't see the money can't decide — and a visitor who can't decide never becomes a lead.
Planning ranges for Marin County, as of Nov 2026. Ranges are estimates, not bids. The Marin ADU cost guide carries the full anatomy — what's included, what's not, and what drives your number up or down — and Mill Valley's cost page shows that town's real fees and permit record.
How it works
The homeowner never has to become an expert — that's our job. The same checker sits at the foot of every guide on this site, and it is the only door.
01
One short form — address, town, what kind of home, what you want, what it's for, when, budget — and, after your verdict, your name and the best way to reach you, so the plan can actually arrive.
~60 seconds · works on a phone
02
What fits, what your town allows, what it should cost, and what could slow it down — hillside, septic, fire zone, HOA. Answered for your lot, not in general, with the unknowns named instead of hidden.
Your town's actual fees & rules
03
With your separate OK, your checker answers become a quote brief offered to the matched roster for your territory — never more than three licensed contractors, and only roster contractors ever see leads. You may receive up to 2–3 comparable quotes and you choose; contractors are named before any introduction. Honest status: the founding roster is enrolling and no builders are listed yet — checked homeowners are first in line for matching when seats fill, and the plan is theirs in full either way. The full model, published →
Up to 2–3 quotes · your OK first · never sold to a list
See what a plan looks like
No architectural jargon, no homework. This sample shows what a readable plan looks like: a layout in plain words, next to the verdict — what you can build, what it should cost, and what happens next. The free checker gives you the verdict half today, for your own lot. It does not draw a layout: that comes from the designer or builder you hire, and so do the technical permit drawings (the city's construction paperwork).
ADU Build Works
adubuildworks.com · Lot plan
SAMPLE PLANIllustrative only — not drawn for any real lot
Sample / illustrative plan. One typical layout, drawn to show what a readable plan looks like — a sample, not a professionally prepared design for a specific property. The checker does not draw a layout for your lot; your designer or builder does, from its size, its setbacks (the required gaps between the ADU and your fences) and your town's rules.
What the verdict says, in plain language:
What you can build — in pictures
Representative photos of the ADU types our guides price — each with its Marin planning range right on the picture, so the dreaming and the deciding happen together.
$300k – $500k · 1-bed, Marin
The Marin classic: a standalone home in the garden — for parents, adult kids, or a tenant. One unit, or two under the new law.
$120k – $220k
The garage door comes out, a front door and real windows go in — and the space you already have becomes a home. The fastest, cheapest route to an ADU.
$250k – $400k
The garage stays — the home goes on top. A smart answer for smaller lots: a full apartment upstairs, parking kept below.
JADU $80k – $180k
What conversions and cottages feel like from the sofa: a real kitchen, room for a bed and a couch, and light all day. This is the part that surprises people — in a good way.
$250k – $450k
Factory-built or contemporary designs that land faster on flatter lots — and for anyone who wants the build measured in weeks on site, not months.
Planning ranges are estimates, not bids — a builder's site visit produces the exact number. Town-specific numbers live on the cost pages: start with the Marin cost guide.
Coverage
Coverage follows the money, not the map. Marin stays the foundation; San Francisco's first five guides are live now, ahead of the January 1, 2027 opening; Napa and the northern arc follow in the next waves.
Every guide carries its jurisdiction's real fees, rules and permit picture — or it doesn't ship.
Questions, answered
For most Marin single-family lots, yes — California law guarantees at least one ADU (including an 800 sq ft state-exempt unit) on a single-family lot, and many lots fit more. What decides your answer is your town's rules, your lot's flags (hillside, septic, fire zone, HOA) and the type you want. That's exactly what the checker screens, in about 60 seconds.
Cost and speed run garage conversion → JADU → above-garage → detached; privacy and rental value usually run the other way. The cost guide lays the types side by side, and your verdict recommends a starting type for your lot and budget.
It can. For townhouses and condos the CC&Rs sit alongside the town's rules, and some communities restrict or effectively block ADUs. The checker branches on your answer and your plan starts with an HOA/CC&R check — before any design money is spent.
Likely yes, if you start in time: the county waives up to $2,500 per ADU and $1,500 per JADU (more for deed-restricted units) through December 31, 2026. The fee-waiver guide has the tiers, the conditions and the application steps. Inside incorporated towns, your town's own fees apply instead.
Your plan comes to you on the channel you picked. Your record is stored only when our system confirms it (you'll see that confirmation on screen — never a fake "received"). If you tick the quotes box, your brief is offered to the matched roster for your territory — at most 3 licensed contractors, and only roster contractors ever see leads — so you may receive up to 2–3 comparable quotes and choose. The founding roster is enrolling and no builders are listed yet, so a stored brief today is first in line for matching when seats fill; nothing is shared with any contractor before seats fill and contractors are named. Full model: How it works.
One address is all it takes to find out what fits, what it costs, and who can build it. The checker is the whole site in one form — everything else just brings you to it.
Check my lot — free →