Buying Coastal Property in Sonoma and Marin: Permits, Bluffs and Septic

A coastal development permit is the approval California’s Coastal Act requires for most development in the coastal zone, and on the Sonoma and Marin coast it is issued by the county under its Local Coastal Program, with some decisions appealable to the California Coastal Commission. For a buyer, the permit rules decide whether you can add a room, replace a septic system, rebuild after a loss or rent the house to visitors. They also explain why so many coastal homes come with permit questions that inland houses don’t.

This post covers both coasts: Bodega Bay, The Sea Ranch, Jenner and the rest of the Sonoma coast, and Dillon Beach, Tomales Bay, Point Reyes, Bolinas, Stinson Beach and Muir Beach in Marin. It explains what counts as development, what is exempt, how bluffs and septic systems change the answer, which hazards the disclosure form leaves out, and the rental rules in each county as of October 2026.

The Coastal Act and the two Local Coastal Programs

The California Coastal Act (Public Resources Code section 30000 and following) sets statewide policies for the coast. Coastal counties carry them out through a Local Coastal Program: a land use plan plus implementing zoning, certified by the Coastal Commission. With a certified program, the county issues most coastal permits itself, while the Commission keeps direct authority over tidal and offshore areas.

Sonoma’s update took several steps. Permit Sonoma says the Board of Supervisors adopted the updated plan on July 17, 2023, the Coastal Commission conditionally certified it on November 14, 2024, and the Board adopted it as certified on February 4, 2025. The county is carrying it out by amending its Coastal Zoning Ordinance and Coastal Administration Manual, so check which version of the zoning applies to your parcel.

Marin’s bay shoreline is a different regime. Our guide to Marin waterfront homes covers BCDC permits for Belvedere, Tiburon and Sausalito.

What counts as development, and what’s exempt

“Development” is broad. Permit Sonoma’s coastal plan FAQ says activities are considered development unless the plan lists them as exempt, and gives lot line adjustments, special events and road maintenance as examples.

Statutory exemptions

Public Resources Code section 30610 says “no coastal development permit shall be required” for several categories. The ones buyers ask about:

• Improvements to an existing single-family home, except classes the Coastal Commission has identified as risky.
• Repair and maintenance that doesn’t enlarge what is being repaired.
• Replacement after a disaster, if the new structure conforms to zoning, serves the same use, sits in the same place and doesn’t exceed the destroyed structure’s floor area, height or bulk by more than 10 percent.

When a home improvement still needs a permit

The Commission’s regulation, 14 CCR section 13250, lists home improvements that aren’t exempt. A permit is required for improvements:

• on a beach, in a wetland, seaward of the mean high tide line, in an environmentally sensitive habitat area or in a highly scenic area designated in a certified plan;
• “within 50 feet of the edge of a coastal bluff”;
• that expand or construct water wells or septic systems;
• between the sea and the first public road, or within 300 feet of the beach, that add 10 percent or more of floor area or raise height by more than 10 percent, or that add structures such as garages, fences, docks or shoreline protective works.

The regulation also treats guest houses and self-contained residential units as separate from the main house, so a second unit isn’t simply an “improvement” to it. That matters if you’re planning an ADU near the coast.

Marin’s categorical exclusions

Marin has Coastal Commission orders that exclude some projects in mapped areas. Examples on the county’s page:

• An addition of no more than 50 percent of existing floor area or 1,000 square feet, whichever is less, if it meets zoning. It doesn’t apply to structures built before 1930 or within the historic boundaries of Tomales, Marshall, Point Reyes Station, Olema, Inverness, Bolinas or Stinson Beach.
• New homes on vacant legal lots in mapped exclusion areas of Olema, Old Dillon Beach and Tomales, and in the Oceana Marin subdivision with an engineered foundation plan and a sewer capacity certification from the North Marin Water District.

The exclusions generally don’t reach tidelands, wetlands or beaches, and the exclusion must be approved before the building permit is issued.

Appeals to the Coastal Commission

A county permit isn’t always final. Permit Sonoma’s coastal plan FAQ (updated March 2024) lists where approvals can be appealed to the Coastal Commission: between the first public road and the sea, within 300 feet of a beach (or of the mean high tide line where there is no beach), within 300 feet of a coastal bluff edge, and within 100 feet of a wetland, estuary or stream. The FAQ also explains when a principally permitted use can be appealed, so ask Permit Sonoma how those rules apply to your project.

For a buyer, appealability adds time and uncertainty to a remodel or new home. Measure the lot against those distances before you count on a project.

Bluffs, erosion and seawalls

Bluff-top lots carry the hardest rules on either coast. The Coastal Act requires new development to “assure stability and structural integrity” and not to require protective devices “that would substantially alter natural landforms along bluffs and cliffs” (Public Resources Code section 30253). Section 30235 allows seawalls and revetments mainly where they’re needed for coastal-dependent uses or to protect existing structures or public beaches from erosion.

In practice, that means a buyer shouldn’t assume a future seawall will protect a bluff-top house. Before you buy:

1. Ask the county which bluff setback standard applies and whether a geologic or geotechnical report is required for your plans.
2. Get the existing reports, permits and any recorded conditions from the seller, including any condition about future shoreline protection.
3. Have a geotechnical engineer look at the bluff, drainage and foundation during your inspection period.

Bolinas and Stinson Beach show how erosion and flooding shape a whole town; our Bolinas and Stinson Beach guides cover their seawall and sea-level-rise history.

Septic systems and water near the coast

Most coastal homes outside a few districts rely on septic, and coastal rules make septic work a permit question twice over: the health department’s permit and, because 14 CCR 13250 names septic construction and expansion, often a coastal permit too.

• Marin: our guide to Marin County septic systems explains which agency regulates which systems, including the separate program in Stinson Beach, and where the county’s rule update stands.
• Sonoma: Permit Sonoma’s well and septic staff handle systems in the unincorporated county, and some coastal communities are on district sewers instead. See our post on wells, septic and rural utilities in Sonoma County.

Septic capacity often sets the limit on bedrooms, ADUs and rentals, so check it before you plan any of them. Water matters as much: several coastal towns depend on small districts or wells, which our town guides for Bodega Bay, Inverness and Dillon Beach describe.

Tsunami and sea-level rise: what the disclosure misses

California’s Natural Hazard Disclosure Statement covers FEMA flood zones, dam inundation, fire hazard zones, earthquake fault zones and seismic hazard zones (Civil Code section 1103.2). It has no line for tsunami or sea-level rise.

The California Geological Survey publishes tsunami hazard area maps for coastal counties, including Sonoma and Marin. CGS says they are “intended for local jurisdictional, coastal evacuation planning uses only” and “do not meet disclosure requirements for real estate transactions.” Look up the address anyway: it tells you whether the home is in an area emergency planners expect to evacuate.

For sea-level rise, read the county’s plan and any community study, and get a flood insurance quote early in escrow. Our guide to the natural hazard disclosure report explains what a commercial report adds to the state form.

Vacation rentals on the coast

Rental income is a common part of the plan for a coastal second home, and the rules differ sharply by county.

Marin

Marin’s October 2026 short-term rental procedures cap licenses at 1,200 across the unincorporated county, excluding Dillon Beach, which has its own cap of 204. Township caps include Stinson Beach 192, Inverness 86, Bolinas 54, Marshall 27, Point Reyes Station 26, Muir Beach 19, Tomales 11 and Olema 3.

Where demand exceeds the cap, owners join a waitlist and get 30 days to apply when a license opens. Licenses last two years, and ADUs created after January 1, 2020 that meet the criteria for a statewide ADU exemption can’t be licensed. Our post on short-term rental rules in Marin County covers the rest, including what happens to a license at sale.

Sonoma

Permit Sonoma says vacation rentals are allowed with a permit in the Coastal Zone. Rentals need a vacation rental permit, a certified vacation property manager, a vacation rental license and compliance with performance standards, and they aren’t allowed in R1, R2 or R3 zones, on Williamson Act land or in ADUs.

Our post on Sonoma County vacation rental rules explains the process. At The Sea Ranch, association rules apply on top; see our Sea Ranch guide.

If rental income matters to the purchase, confirm the parcel’s eligibility and the status of any existing permit or license in writing before you remove contingencies. Diamond may refer you to partners we work with; you’re free to choose any provider.

A coastal buyer’s checklist

1. Confirm the parcel is in the coastal zone, and whether it’s in an appealable area.
2. Pull the permit history: coastal permits, exclusions or exemptions, and building permits with final sign-offs.
3. Compare the permits with what’s built, especially decks, second units and septic.
4. Get the septic and water records from the county or district.
5. Check FEMA flood, tsunami and fire maps, and get insurance quotes.
6. For a bluff lot, get a geotechnical review and read any recorded permit conditions.
7. Confirm rental eligibility and license status in writing.

Small coastal towns like Jenner have their own quirks, from estuary flooding to slide-prone highways, so read the town guide alongside this one.

Questions people ask

Do I need a coastal development permit to remodel my house?

Not always. Improvements to an existing single-family home are generally exempt, but not if the home is within 50 feet of a bluff edge, on a beach or wetland, or near the shoreline and the work adds 10 percent or more of floor area or raises the height by more than 10 percent. Building or expanding a septic system or well also needs a permit.

Can I rebuild after a fire or storm without a coastal permit?

Often, under the disaster replacement exemption, if the new structure conforms to zoning, serves the same use, is in the same location and is no more than 10 percent larger in floor area, height or bulk.

Where does the coastal zone end in Sonoma County?

Permit Sonoma describes it as running from the first coastal ridgeline to three miles out to sea. Check the parcel’s zoning and the county’s coastal zone map for a specific lot.

Is Sonoma County’s new Local Coastal Plan in effect?

Yes. Permit Sonoma says the Board adopted the plan as certified by the Coastal Commission on February 4, 2025, and it is now in effect, with the coastal zoning ordinance being amended to carry it out.

Do tsunami maps appear on the natural hazard disclosure?

No. The state form has no tsunami line, and the Geological Survey says its tsunami maps don’t meet real estate disclosure requirements. Check them yourself.

How many short-term rental licenses does Stinson Beach allow?

Marin’s October 2026 procedures list 192 for the Stinson Beach township, with a waitlist when licenses are full.

If you’re looking at a home on the Sonoma or Marin coast, we can pull its permit history, septic records and rental status with you before you write an offer. Start with our buyer services.

This is general information, not legal advice; talk to a California land use attorney or the county planner about your property.

Sources & notes

• California Public Law: Public Resources Code section 30610 (permit exemptions)
• Cornell Legal Information Institute: 14 CCR 13250 (improvements to existing single-family residences)
• California Public Law: Public Resources Code section 30253
• California Public Law: Public Resources Code section 30235
• California Public Law: Civil Code section 1103.2
• Permit Sonoma: Local Coastal Plan Update
• Permit Sonoma: Local Coastal Plan frequently asked questions
• Permit Sonoma: Vacation rentals
• County of Marin Planning: Local Coastal Program
• County of Marin: Coastal permit categorical exclusions
• County of Marin: Short-term rental administrative procedures (October 2026)
• California Geological Survey: Tsunami hazard area maps

Bluff setback distances, current septic code details and sea-level-rise disclosure proposals aren’t stated here because we didn’t verify them for this post; ask the county for the standard that applies to your parcel.

Last reviewed October 2026 by Matthew Martinez.