Building permits, zoning and land rules in Marin County, California

At a glance

Building permit

Required for most construction in unincorporated Marin County; narrow exceptions apply¹

Zoning

Title 22 governs all unincorporated areas; cities and towns have their own rules⁴⁵

Septic permits

Environmental Health Services permits new, replacement, repair, alteration and abandonment work⁶³

Owner-builder

A contractor-license exemption is available under conditions, but permits and inspections still apply⁷

RV living

Ordinary residential occupancy is not confirmed; camping is limited to campgrounds and hunting and fishing camps⁸⁹

Tiny homes

The county confirms only a temporary emergency-housing pathway; ordinary use depends on structure type and parcel zoning¹⁰¹¹

ADUs

Allowed in unincorporated Marin subject to building, zoning, water and wastewater requirements¹²

Septic soils

Only 1.6% of county soils lack severe limits for a conventional drain field¹³

Who to call

Contact details are copied from each office’s official page and were checked against it on October 16, 2026.

Do you need a building permit in Marin County, California?

Most construction projects in unincorporated Marin County require a building permit from Building and Safety¹. A one-story detached, non-habitable accessory structure may be exempt when it is no larger than 120 square feet and complies with zoning; a rural tool shed, workshop or horse stall may qualify at up to 300 square feet on a parcel of at least one acre, again subject to zoning¹. If the work is not on the county's exception list, assume a permit is needed and ask Building and Safety before starting¹. Permitted projects require inspections, and separate reviews or fees may come from Planning, Public Works, Fire, or Environmental Health Services¹⁴. Marin County Code Chapter 19.20 also offers voluntary alternative regulations for limited-density owner-built rural dwellings, and the community development agency issues a certificate of occupancy identifying compliance with that chapter once the work is approved¹⁵. The County Board of Supervisors adopted the updated California Building Standards Code with Marin amendments on December 9, 2025, and the updated state regulations took effect January 1, 2026¹⁶. The 2025 code and Marin-specific local amendments apply in unincorporated Marin, including updated green-building requirements effective January 1, 2026¹⁷. A Marin-specific restriction also prohibits fire-retardant treated wood in exterior construction within designated Wildland Urban Interface and Very High Fire Hazard Severity Zones, so ask Building and Safety whether the parcel falls in one before choosing materials¹⁶.

Who issues Marin County building permits, and how do you reach them?

Marin County Community Development Agency's Building and Safety Division handles permits, plan review and inspections for unincorporated Marin County¹⁸. The office is at 3501 Civic Center Drive, Suite 308, San Rafael, CA 94903, and its general number is 415-473-6550¹⁸. The county uses two application paths: quick online permits for listed maintenance and minor improvements, and plan review for new buildings, additions, remodels, conversions, ADUs, decks, accessory structures, pools and similar larger work¹⁹. All building permits begin through the county's online application, and plans for larger projects are submitted electronically and drawn to scale¹⁹²⁰. After issuance, schedule each required inspection with Building and Safety; the inspector checks the approved permit documents and the work covered by the permit¹⁴.

Does Marin County have zoning?

Marin County Title 22 contains the zoning and subdivision rules for every unincorporated area⁴. Inside city and town limits the local council sets planning and zoning instead, as in San Rafael²¹, Novato²², San Anselmo²³, Corte Madera²⁴ and Tiburon²⁵; the county's zoning rules below do not apply there². Use the Planning Division's parcel lookup to identify the district before applying a dimensional standard²⁶. Agricultural districts have parcel-specific minimum lot areas and height limits; primary structures in the listed agricultural districts generally have a 30-foot limit, while accessory structures in A15 through A60 districts have a 16-foot limit, subject to the code's measurement rules and exceptions²⁷²⁸. Sleepy Hollow parcels zoned R1:BD or A2:BD require at least 1,300 square feet of habitable floor area, excluding porches and garages²⁹. An ADU is allowed in unincorporated Marin: a Category 1 detached ADU is limited to 800 square feet, a Category 2 detached ADU generally to 1,200 square feet, rentals must run longer than 30 consecutive days, and the Director must decide a complete ADU permit application within 60 days; building, zoning, water, wastewater and septic requirements still apply³⁰. Ask Planning which standards and overlays apply to the exact parcel³¹.

How do septic permits work in Marin County?

Septic permits for any Marin County address, city or not, are the county's to issue. Marin County Environmental Health Services administers onsite wastewater treatment systems and requires a construction permit for a new septic system⁶³. Permits also cover listed replacement, repair, alteration and abandonment work, while additional permission may be needed in the Coastal Zone or Stream Conservation Area³². Environmental Health Services performs construction inspections, and the septic tank and disposal area cannot be covered before the Health Officer's inspection³³. Alternative systems require annual operating permits and professional monitoring³³. A property within 400 feet of a public sewer main must connect instead of expanding septic when the Health Officer finds connection physically and legally possible³⁴. Only 1.6% of Marin County soils lack severe limits for a conventional drain field, so a site evaluation should precede a land purchase or house design¹³. Simple graywater systems below 250 gallons per day may avoid a construction permit but still require advance notice, while larger or treated systems require county permits³².

Can you live in an RV or tiny home on land in Marin County?

Marin County has not confirmed a general right to live in an RV on a private parcel, and California generally limits RV occupancy to regulated mobilehome or special-occupancy parks unless a local ordinance provides otherwise³⁵. In unincorporated Marin County, camping may occur only in campgrounds and hunting and fishing camps and is limited to 30 days per calendar year per person, except camp staff; the applicable agricultural district may prohibit the use or require a Use Permit⁸. The Board of Supervisors declared a shelter crisis on March 11, 2025, for three years; paired with building-code changes, it allows removable cabins or RVs as temporary emergency shelter only in unincorporated areas and only for someone currently designated as homeless³⁶. Private owners may add such shelter without a permanent foundation under that rule, but it is not general authorization for residential RV occupancy³⁶⁹. Tiny homes need a recognized legal structure classification under California rules¹¹. On a single-family residential parcel, an RV may house dedicated caregivers for occupants who need medical care and help with daily activities, but only under a Temporary Use Permit that cannot run longer than 6 months³⁷. Marin's emergency tiny-home pathway is temporary and cannot be used as a short-term rental¹⁰. Manufactured-home rules for mobile-home parks do not authorize a unit on every parcel; those parks require the applicable health permit, rezoning petition and Master Plan³⁸.

Building a home in Marin County: the steps, in order

1. Confirm that the parcel is unincorporated, then use the Planning Division's zoning lookup and ask about allowed use, setbacks, flood districts and Coastal Zone constraints⁵²⁶. A qualifying agricultural project in the Coastal Zone needs an approved Coastal Permit Exclusion before building, septic or well permits can issue³⁹.

1. Confirm legal access because every structure or use must reach a public street through frontage, an easement or a recorded mutual-access agreement acceptable to the Director⁴⁰. A driveway in a state highway right-of-way also needs a Caltrans encroachment permit⁴¹.

1. Resolve water and wastewater before final design; new and replacement septic systems require county review, and only 1.6% of local soils lack severe conventional-drain-field limits³¹³. A private well in unincorporated Marin needs an Environmental Health Services permit before drilling and another permit before its water is used domestically⁴².

1. Start the correct online building-permit path and submit scaled electronic plans when plan review is required¹⁹²⁰.

1. Pay applicable fees, obtain the permit, and complete each required inspection before covering work⁴³¹⁴.

What should you check before buying land in Marin County?

Check the exact zoning district, jurisdiction and development overlays before relying on a listing description⁵²⁶. In Marin's Primary Floodway district, new buildings and structures are prohibited; the Secondary Floodway district allows underlying uses only under standards and agreements protecting ponding and drainage capacity⁴⁴⁴⁵. On qualifying undeveloped parcels in the San Geronimo Valley Stream Conservation Area, an exception analysis limits total parcel coverage to 1,000 square feet and requires the least possible stream-area encroachment⁴⁶. Verify road access, wastewater feasibility and water before closing because only 1.6% of county soils lack severe conventional-drain-field limitations⁴⁰¹³. Drilling a private well in unincorporated Marin requires a county permit, and domestic use of the installed well requires a permit to operate⁴². Splitting a parcel is regulated by the county's subdivision rules in Title 22 Article VI, which work alongside the California Subdivision Map Act and add zoning-district and slope-based minimum lot areas⁴⁷. It needs County approval, generally a Tentative Map and then a Parcel Map or Final Map, and subdivisions creating 5 or more parcels generally need Tentative and Final Maps⁴⁸. If rental income matters, residential rentals shorter than 30 days require county licensing, subject to a countywide cap and township-specific limits⁴⁹. Marin County's effective property-tax rate is about 0.7%, and the median annual property-tax bill is about $10,001⁵⁰⁵¹.

Watch-outs

• A permit exemption does not waive Marin County zoning: even a qualifying small accessory structure must comply with the parcel's zoning rules¹.
• Marin County's shelter-crisis authorization for RVs and tiny homes runs three years from March 2025, is limited to people currently designated as homeless, and does not establish ordinary residential occupancy on private land³⁶¹⁰.
• Development in Marin County's Primary Floodway district is far more constrained than ordinary underlying zoning because new buildings and structures are prohibited there⁴⁴.
• Camping in unincorporated Marin County is confined to campgrounds and hunting and fishing camps, with district-specific prohibitions or Use Permit requirements⁸.
• An ADU in unincorporated Marin County still must meet applicable building, zoning, water, wastewater and septic requirements¹².
• In unincorporated Marin County, fire-retardant treated wood is prohibited in exterior construction within designated Wildland Urban Interface and Very High Fire Hazard Severity Zones¹⁶.

Sources

1. Do I need a building permit?, quoted and re-checked
2. Title 22 - Development Code, quoted and re-checked
3. Septic systems/onsite wastewater treatment systems, quoted and re-checked
4. Title 22 - Development Code, quoted and re-checked
5. How your County government works, quoted and re-checked
6. Septic systems/onsite wastewater treatment systems, quoted and re-checked
7. Owner-Builder Overview, quoted and re-checked
8. Title 22 - Development Code, quoted and re-checked
9. County Declares Shelter Crisis to Provide Temporary Emergency Housing, quoted and re-checked
10. Emergency temporary housing under Marin's Shelter Crisis, quoted and re-checked
11. Information Bulletin 2016-01: Tiny Homes (California statewide rule), quoted and re-checked
12. Accessory dwelling units (ADUs), quoted and re-checked
13. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
14. Schedule a building inspection, quoted and re-checked
15. Marin County Code, Chapter 19.20, Voluntary Alternative Regulations for Limited Density Owner-Built Rural Dwellings, quoted and re-checked
16. marincounty.gov, quoted and re-checked
17. marincounty.gov, quoted and re-checked
18. Marin County Community Development Agency - Building and Safety (marincounty.gov)
19. How to apply for a building permit, quoted and re-checked
20. Submit plans before starting a big job, quoted and re-checked
21. San Rafael: SRMC 14.16.240 Manufactured homes (Marin County), quoted and re-checked
22. Novato: Novato Code, Chapter XIX Zoning, 19.60.020 Definitions (Marin County), quoted and re-checked
23. Town of San Anselmo: San Anselmo Code 10-3.412 Maximum Floor Area and Lot Coverage, Single-Family Below 150 MSL (Marin County), quoted and re-checked
24. Town of Corte Madera: Corte Madera Municipal Code § 18.08.220 (Marin County), quoted and re-checked
25. Town of Tiburon: Tiburon Code 16-100.020 Definitions (Marin County), quoted and re-checked
26. Title 22 - Development Code, quoted and re-checked
27. Marin County Code - Title 22, Development Code, quoted and re-checked
28. Marin County Code - Title 22, Development Code, quoted and re-checked
29. assets.marincounty.gov, quoted and re-checked
30. Title 22 - Development Code, quoted and re-checked
31. Marin County Community Development Agency - Planning Division (marincounty.gov)
32. Graywater systems, quoted and re-checked
33. Septic systems/onsite wastewater treatment systems, quoted and re-checked
34. Regulations for Design, Construction and Installation of Individual Sewage Disposal Systems, quoted and re-checked
35. hcd.ca.gov (California statewide rule), quoted and re-checked
36. County Declares Shelter Crisis to Provide Temporary Emergency Housing, quoted and re-checked
37. Chapter 22.50 - Temporary Use Permits, quoted and re-checked
38. Marin County Code Title 22 Development Code, quoted and re-checked
39. Coastal Permit Categorical Exclusions, quoted and re-checked
40. 2023 Development Code, quoted and re-checked
41. Encroachment Permits | Caltrans (California statewide rule), quoted and re-checked
42. Private water wells, quoted and re-checked
43. Planning Division Fees, quoted and re-checked
44. Marin County Code - Title 22, Development Code, quoted and re-checked
45. Marin County Code - Title 22, Development Code, quoted and re-checked
46. Marin County Code - Title 22, Development Code, quoted and re-checked
47. Title 22 - Development Code, quoted and re-checked
48. Title 22 - Development Code, quoted and re-checked
49. Short Term Rental (STR) License, quoted and re-checked
50. Effective property tax rate: Bolthole Index county data
51. Median property tax bill: Bolthole Index county data

Written October 16, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.