How much does it cost to build an ADU in Marin County? The usual ADU job filed with Marin County is $205,000, from 111 priced permits (October 2023 through September 2026). A filed value is what the contractor wrote on the permit, not a quote or the final bill.
The usual ADU job filed with Marin County is $205,000, from 111 priced permits, October 2023 through September 2026. Half of jobs were filed for less, half for more. A filed value is what the contractor wrote on the permit, not a quote or the final bill. An ADU permit here usually takes 555 days from issue to final inspection. How long permits take →
Approximately, from each firm's own spread: every firm's range of filed values, weighted by its 111 priced permits across 99 firms, pooled into one. Half of Marin County (unincorporated) ADU permits were filed between $92,600 and $376,000.
| Percentile | Filed value | Reads as |
|---|---|---|
| 10th | $39,900 | 1 in 10 permits filed below |
| 25th | $92,600 | 1 in 4 filed below |
| 50th | $207,000 | the middle permit |
| 75th | $376,000 | 1 in 4 filed above |
| 90th | $612,000 | 1 in 10 filed above |
Firms split into thirds by the usual value of the homes they work on, with each third's usual filed value weighted by permits. Home values: Marin County assessed land and improvement values from MarinMap parcels (Proposition 13 values, which usually sit well below market value). Under Proposition 13 a home bought decades ago can carry a value far below what it would sell for today, so treat the home-value matching and the price-versus-similar-jobs comparison as rough.
| Firms working on | Usual home value | Usual filed value | Firms | Permits |
|---|---|---|---|---|
| Lower third | under $1,333,602 | $100,000 | 32 | 34 |
| Middle third | $1,333,602–$2,491,376 | $300,000 | 33 | 36 |
| Upper third | $2,617,676 and up | $200,000 | 33 | 40 |
Top 10 by permits in the last 12 months. Usual is each firm's middle filed value; middle half is the range its middle half of jobs were filed in; both are shown for firms with 5 or more priced permits. Busy is not the same as careful: pick what you value to build a list.
| Firm | Permits | Last 12 mo | Usual |
|---|---|---|---|
| Cohan Structures | 3 | 2 | — |
| Kelly Domer Partners Inc. dba Pacific Constr | 3 | 2 | — |
| Emr Construction Inc | 4 | 1 | — |
| Natomas Labs Inc, dba Villa Homes | 2 | 1 | — |
| Hildebrand Renovation | 2 | 1 | — |
| Precedent Construction | 1 | 1 | — |
| Avilas Construction Inc | 1 | 1 | — |
| Bob Ellison Woodworking | 1 | 1 | — |
| Kieran Collins Construction | 1 | 1 | — |
| I Construction & Structural Inc | 1 | 1 | — |
Line your quote up against the file. In Marin County (unincorporated), 1 in 10 ADU filed values sit under $39,900, the middle half between $92,600 and $376,000, and 1 in 10 over $612,000.
Marin County files the fewest ADU permits in February (32 against an average month of 100) and the most in April (173). If you can choose, ask for quotes in a quiet month. We have no prices by month, so this is about crews' schedules, not a discount. When each trade is busiest in Marin County →
Source: Marin County Community Development Agency building permits on homes in unincorporated Marin (the County's open-data permit and inspection files). The window is October 2023 through September 2026; a permit filed after that isn't here yet.
Usual is the middle permit: half were filed for less, half for more. Only permits with a filed value count; a value of $0 or none is left out.
The spread is approximate: we keep seven points of each firm's own range of filed values, not every permit, and pool them.
Nobody paid to be on this page and nobody can. How the records work in Marin County (unincorporated) →
ADU cost in other cities: Nashville Raleigh Denver San Diego Honolulu Palo Alto Bellingham San Francisco Anaheim Sacramento County (unincorporated)
Other job costs in Marin County (unincorporated): Roofing · HVAC · Electrical · Solar & Battery · Kitchen, Bath & Remodel · Windows & Doors · Water Heater · Plumbing & Gas · Foundation & Retaining Wall · EV Charger · Siding & Stucco · Pool & Spa · Decks & Stairs · Addition