Multifamily and Duplex Properties for Sale in Muir Beach: Zoning and Rent Rules

What multifamily in Muir Beach looks like

Muir Beach has no apartment buildings. It is a small coastal village of single-family homes, many with a cottage, studio or ADU, hemmed in by federal and state parkland. The county’s LCP Unit I calls the community essentially built out, with surrounding lands planned for agriculture. In practice, "multifamily" here means a home with a permitted ADU or JADU, or a rare older parcel with two legal homes. For financing a two-unit property, see financing 2-4 unit properties; apartment building loans are unlikely to be relevant.

Where the zoning allows it

Muir Beach is entirely in the Coastal Zone, under county Chapter 20.62. Recent county permits show the common zoning: C-RA-B1 at APN 199-221-21, and C-RA:B-2 with a C-SF5 (2–4 units per acre) plan designation at 20 Sunset Way.

The coastal code treats densities as maximums, not entitlements. The county’s West Marin housing sites list includes no Muir Beach sites.

ADUs. ADUs are the main way to add a unit, and they usually need a Coastal Development Permit. The 2025 approval at APN 199-221-21 allowed a 750-square-foot ADU over a garage, 15 feet tall, with a replacement septic system. A pending permit at 20 Sunset Way proposes a 484-square-foot detached ADU. See our ADU investment guide.

SB 9. SB 9 applies only in urbanized areas and urban clusters and has coastal limits. Assume it does not apply in Muir Beach unless the county confirms otherwise; see our SB 9 lot split guide.

Rent rules: state law plus county ordinances

Rent cap. No local cap applies. The Attorney General’s rent cap page sets the AB 1482 cap for the San Francisco area, which includes Marin, at 8.8% for increases from August 1, 2026 through July 31, 2027. Most Muir Beach rentals are single-family homes owned by individuals, which can be exempt with proper notice. See our AB 1482 guide.

County just cause. Chapter 5.100, Ordinance 3705 of December 2018, covers properties with three or more units on one legal lot. Permitted ADUs and JADUs do not count, but unpermitted units and STR units do. A Muir Beach home with an unpermitted studio and a permitted ADU may still be outside it, while one with two unpermitted cottages may be inside it. See our just cause eviction guide.

Mediation. Increases above 5% in 12 months go to the county’s mandatory mediation program if the tenant asks within 10 calendar days.

Muir Beach rental property rules

• Short-term rentals. Muir Beach is a capped STR township. The county’s administrative procedures list 20 initial licenses, falling to 19. A buyer joins a waitlist; licenses do not simply pass with a sale, and certain ADUs built after January 1, 2020 cannot be licensed.
• Business license and registry. Every rental needs a county business license, $15 per dwelling unit per year. Units covered by just cause must be in the county rental registry.
• Source of income. The county’s Renting in Marin page bars discrimination against voucher holders.

Water, septic and creek limits

Water. The Muir Beach Community Services District serves 159 paying customers from two wells and Redwood Creek watershed sources. It stores about 12 days of supply in a 200,000-gallon tank built in 2010 and an older 100,000-gallon redwood tank, and can deliver up to 45,000 gallons per day. Marin LAFCo’s West Marin review recommended more storage and emergency interties. Ask the CSD whether an added unit needs a new meter or charges.

Septic. There is no sewer. Many Muir Beach ADU permits include septic replacement, as the 2025 approval did. Budget for a septic evaluation before you count on a second unit.

Redwood Creek. LCP Unit I notes that Redwood Creek supports steelhead and silver salmon runs and that septic effects on the creek have been monitored. Creekside parcels should expect stricter wastewater and setback review.

Older homes and fire. Many homes are older wood-frame houses on steep lots. Consider a seismic retrofit check. SB 721 rarely applies, since it covers buildings of three or more units, but see our SB 721 guide if a parcel has three units with elevated decks. The volunteer Muir Beach fire department and the CSD’s wildfire prevention membership matter for insurance.

Coastal permits and the categorical exclusion map

The 2019 certified LCP Land Use Plan, adopted by the Board of Supervisors in 2018 and certified by the Coastal Commission on February 6, 2019, gives Muir Beach its own land use policy map and categorical exclusion area map. The exclusion map matters to an owner because some minor residential work inside a mapped exclusion area can skip a full Coastal Development Permit, while the same work outside it cannot. The Lance Angel approval shows the usual path for a new unit: the county required a full CDP because the project was not otherwise exempt under Section 20.68.030. The LUP also caps most new construction in the coastal zone at 25 feet, and the county can set lower heights to protect public views. In a village surrounded by national parkland, view and visual review can shape a second unit as much as zoning does.

Underwriting a Muir Beach multifamily purchase

1. Confirm the coastal zoning and the permit status, including coastal permits, of every unit.
2. Get CSD water service records and confirm whether added units have meters.
3. Get septic permits, capacity and any repair history.
4. Separate long-term rent from STR income, and verify license status and renewal limits.
5. Classify tenancies under AB 1482 and county just cause, and collect estoppel certificates.
6. Model insurance, septic reserves and taxes in our rental property analysis.

Questions people ask

Sources & notes

1. Marin County Coastal Zoning Code Ch. 20.62
2. Marin County LCP Land Use Plan Unit I (amended through 2010)
3. Marin County permits: P5846, P5997
4. Marin County, West Marin housing element sites
5. Marin County renter pages: Renting in Marin, Just Cause, Mandatory Mediation
6. Marin County: STR administrative procedures, business license
7. Muir Beach CSD, water system and Marin LAFCo West Marin MSR draft
8. California Attorney General, Rent Caps
9. Marin County 2019 certified LCP Land Use Plan

Note: We did not open the 1978 community plan or county SB 9 eligibility maps, and did not confirm whether any C-R2 or C-RMP parcels exist in Muir Beach.

General information, not legal or tax advice. Last reviewed October 2026 by Matthew Martinez.

Related: Muir Beach real estate guide · Commercial real estate in Muir Beach · Multifamily investing guide · Investor services