Multifamily and Duplex Properties for Sale in Byron: Zoning and Rent Rules

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What multifamily in Byron looks like

Byron is a farm town of about 800 people in unincorporated eastern Contra Costa County, so its rental housing is small scale. It includes older houses and duplexes in the original town blocks, rural homes with second units on agricultural land, mobile homes, and farm employee housing. An investment here is usually a house with an ADU, a duplex, or a small mixed-use building on the old commercial street, not an apartment complex. See financing 2-4 unit properties and apartment building loans.

Where the zoning allows it

Byron is zoned by Contra Costa County under Division 84. Read the county zoning map for each parcel. The districts that allow two or more units are:

District	Units allowed	Key standards
D-1 Two-Family	One duplex per lot	8,000 sq ft minimum lot. Two covered spaces per unit
M-29 to M-6 Multiple Family	Apartments at 6 to 29 units per acre, by district	M-29 needs a 10,000 sq ft lot. Confirm whether any is mapped in Byron
R-6 and other single-family districts	One home plus an ADU and junior ADU. SB 9 where eligible	Lot sizes by district
Agricultural districts	Farm dwellings and, under county and state rules, ADUs and farmworker housing	Williamson Act contracts may limit residences
T-1 Mobile Home Park	Mobile home, travel trailer and RV parks by land use permit	3 acre minimum, 12 units per gross acre, 2,500 sq ft per space

New county projects of five or more units must meet the county’s 15% inclusionary rule under Chapter 822-4, or pay an in-lieu fee for projects up to 125 units. Projects of one to four units are exempt.

ADUs and SB 9. County zoning allows ADUs on residential lots under Chapter 82-24. See our ADU investment guide. SB 9 applies only in urbanized areas or urban clusters, and it excludes prime farmland, some hazard zones and recently tenant-occupied housing. Many Byron parcels are agricultural or rural, so check eligibility parcel by parcel. See our SB 9 lot split guide.

Rent rules: state law only

The Attorney General’s rent cap page lists no local cap for unincorporated Contra Costa County. Covered units in Byron 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 owned by individuals are exempt with the statutory notice. A duplex where the owner lives in one unit is also exempt. Mobile home park spaces fall under the state Mobilehome Residency Law. See our AB 1482 guide and just cause eviction guide.

Byron rental property rules

No local registry or inspection program. We found no county rent registry or rental inspection program for unincorporated Byron. State habitability law and county code enforcement apply.
Farmworker housing. Employee housing for farmworkers is regulated by state law and the state housing department, in addition to county zoning. Confirm the permit status of any bunkhouse or employee units on a farm purchase.
Airport compatibility. Byron Airport sits between the town and the Alameda County line. The county’s 2005 master plan notes that the Byron Airport Land Use Compatibility Plan sets safety zones and that future development must comply with them. The county amended that plan in 2022 as part of the Airport Development Program. Residential density near the runways can be limited, so check the zone for any parcel close to the airport.

Sewer, septic, water and older buildings

Sewer capacity is the real limit on new units in Byron:

Byron Sanitary District. LAFCO’s directory says the district, formed in 1948, collects, treats and disposes of sewage for the Byron community, about 0.53 square miles and roughly 800 residents. A board of five meets monthly. An ADU or duplex inside the district needs a connection and capacity charge. Ask the district about capacity before you buy.
Septic outside the district. Rural parcels depend on septic systems approved by county environmental health. Adding a unit can require a larger or new system.
Water. Byron Bethany Irrigation District supplies farm water. Domestic water may come from wells or small systems, so test potable supply.
Older stock. Town-center houses and small buildings are often pre-1960 wood frame. Get an engineer’s view on seismic retrofit and foundations. A building with three or more units and elevated balconies needs SB 721 inspections.

Underwriting a Byron multifamily purchase

Confirm the county zoning and whether the parcel is inside the Byron Sanitary District.
For ADUs or new units, get sewer capacity or septic approval in writing first.
Check airport compatibility zones and any Williamson Act contract.
Classify each unit under AB 1482, including the owner-occupied duplex and single-family exemptions.
Collect leases, the rent roll and estoppel certificates, and confirm permits for every unit.
Add reassessed property tax, district charges and the county transfer tax of $0.55 per $500 (Clerk-Recorder) in our rental property analysis.

Questions people ask

Does Byron have rent control?

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

Who provides sewer in Byron?

The Byron Sanitary District serves the town, about half a square mile. Rural parcels use septic.

Can I build a duplex in Byron?

Yes, on land zoned D-1 or a county multifamily district, with an 8,000 square foot minimum lot in D-1. Sewer or septic capacity must be confirmed.

Does SB 9 apply in Byron?

Only on eligible parcels. SB 9 excludes prime farmland and some other areas, and many Byron parcels are agricultural.

Does the airport affect housing in Byron?

It can. Parcels near Byron Airport are subject to its compatibility plan, which can limit residential density.

Are mobile home parks allowed?

Yes, in the county T-1 district with a land use permit, on at least 3 acres at up to 12 units per gross acre.

Sources & notes

Note: Zoning of individual Byron parcels, sewer capacity and county farmworker housing provisions were not verified. Inclusionary and D-1 details are drawn from county code reviewed for our Contra Costa County pages.

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

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