Multifamily and Duplex Properties for Sale in Bethel Island: Zoning and Rent Rules

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What multifamily in Bethel Island looks like

"Multifamily" on Bethel Island rarely means an apartment building. The island is an unincorporated Delta community of single-family waterfront homes, mobile home parks, RV parks and marinas with liveaboard and seasonal populations. Rental investment here usually means one of three things: a waterfront house with an ADU or junior ADU, a duplex where the zoning allows it, or a mobile home or RV park. Contra Costa LAFCO’s service review describes housing mostly along the island’s edge and interior roads, plus the Delta Coves subdivision of 495 planned units. For the financing side, see financing 2-4 unit properties and apartment building loans.

Where the zoning allows it

Contra Costa County zones the island under Division 84. Check the county zoning map for each parcel.

District	Units allowed	Key standards
F-1 Water Recreational	One single-family home, plus an ADU and a junior ADU under Chapter 82-24	R-6 lot and height standards. 50 ft from a levee centerline. Two parking spaces per unit.
R-6 and other single-family districts	Single-family homes, ADUs, JADUs	SB 9 may apply where state criteria are met
D-1 Two-Family (where mapped)	One duplex per lot	8,000 sq ft minimum lot
T-1 Mobile Home Park	Mobile home parks, travel trailer parks, RV parks and campgrounds by land use permit	3 acre park minimum, 12 units per gross acre, 2,500 sq ft per space, 200 sq ft of recreation area per space
-FH Flood Hazard combining	Overlay	Elevated single-family homes, duplexes and second units may reach 3½ stories if the lowest story is only parking, storage or access

We did not confirm any M-district apartment zoning on Bethel Island. The 1989 Bethel Island Area Specific Plan draft EIR (CEQAnet) studied about 1,000 new homes on Bethel Island and 2,000 on Hotchkiss Tract. Check with the county whether any of those designations are in force before assuming higher density.

ADUs and SB 9. F-1 lists ADUs and junior ADUs as permitted uses, so a waterfront house can usually add one. See our ADU investment guide. SB 9 lot splits and two-unit projects do not apply in places such as FEMA floodways and some hazard areas without mitigation, so most Bethel Island parcels need case-by-case review. See our SB 9 lot split guide.

Rent rules: state law only

Unincorporated Contra Costa County has no local rent cap on the Attorney General’s rent cap page. Covered units on Bethel Island follow the Tenant Protection Act. Contra Costa is in the AG’s San Francisco Area region, where the cap is 6.3% for increases starting August 1, 2025 and 8.8% for increases from August 1, 2026 through July 31, 2027. Single-family homes and condos owned by individuals can be exempt from AB 1482 with the required notice, and newer Delta Coves homes may fall under the 15-year new-construction exemption. See our AB 1482 guide and just cause eviction guide.

Mobile home parks. Spaces in a mobile home park are governed by the state Mobilehome Residency Law, not AB 1482’s apartment rules. We did not find a county mobile home rent ordinance for unincorporated Contra Costa. Confirm with the county before buying a park.

Bethel Island rental property rules

Short stays. We did not verify county short-term rental rules for the island. Confirm with the Department of Conservation and Development before underwriting vacation rental income.
Levee approvals. BIMID requires its approval for construction, alterations, docks, ramps, levee steps, tree planting and demolition that affect the levee. It replants three trees for each tree removed from levee areas. A project that needs a variance is paused until a variance is filed under Ordinance 18.
Cannabis. The island is in the county’s cannabis exclusion district, which bans commercial cannabis activity, including on rental property.

Flood, levee, water and sewer

These are the real limits on adding units:

Below sea level. LAFCO reports that more than 95% of the island’s roughly 3,500 acres are below sea level, protected by an 11.5-mile levee. BIMID reports the levee meets FEMA standards. Flood insurance and elevation requirements still drive construction costs.
Water. Diablo Water District serves Delta Coves and Beacon West. CSA M-28 serves the Willow Park Marina area and the Willow mobile home park. Most other homes rely on private wells or about 30 small private water companies. LAFCO notes groundwater is often high in iron, manganese and dissolved solids, and some wells exceed the arsenic standard. An ADU on a well needs proof of adequate potable supply.
Sewer. Ironhouse Sanitary District serves the whole island, which helps ADU feasibility compared with septic-only Delta areas. Confirm connection and capacity fees.
Older units. Many island homes and park units are older or modified. Buildings with three or more units and elevated balconies or walkways need SB 721 inspections. Peat soils make foundations and seismic review important.

Underwriting a Bethel Island multifamily purchase

Confirm the county zoning (F-1, D-1, T-1 or single-family) and any -FH overlay, and verify each unit was legally permitted.
Identify the water provider or well, test the water, and confirm Ironhouse sewer service.
Get a flood elevation certificate and a flood insurance quote for every structure.
For mobile home or RV parks, review the land use permit, space count and Mobilehome Residency Law compliance.
Collect leases, the rent roll and estoppel certificates, and check AB 1482 status for each unit.
Model insurance, levee-related taxes, reassessed property tax and the county transfer tax of $0.55 per $500 (Clerk-Recorder) in our rental property analysis.

Questions people ask

Does Bethel Island have rent control?

No local rent control. Covered units follow AB 1482, with an 8.8% cap for increases from August 1, 2026.

Can I add an ADU to a waterfront home on Bethel Island?

Usually. The F-1 zone permits ADUs and junior ADUs under county ADU rules, subject to the 50-foot levee setback and flood elevation requirements.

Who provides sewer on Bethel Island?

Ironhouse Sanitary District serves the entire island.

Are mobile home parks allowed?

Yes, in the T-1 district with a county land use permit, on at least 3 acres at no more than 12 units per gross acre.

Do I need levee district approval to build?

Yes, if the work affects the levee. BIMID must approve home construction, alterations, docks and similar work near the levee.

Is drinking water a concern?

It can be. LAFCO notes island groundwater often has high iron, manganese and dissolved solids, and some wells exceed arsenic standards.

Sources & notes

Note: D-1 and multifamily zoning on the island were not confirmed on the county map. County short-term rental rules and SB 9 eligibility for specific parcels were not verified.

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

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