Can I build two ADUs on my California property?

In most cases, yes — California's statewide ADU law is intentionally generous about allowing additional units, and on many properties you can add more than one. The exact combination depends on whether your lot is single-family or multifamily and on any additional allowances your local jurisdiction provides.

Single-family lots: one ADU plus one JADU

On a typical single-family lot, state law allows one ADU and one JADU (Junior ADU, up to 500 SF created within the existing home). That means a homeowner can often have the main house, a detached or attached ADU, and a junior unit converted from a bedroom or attached space — three independent living arrangements on one lot. Some cities go further under their local ordinances and permit additional ADUs, so it is worth checking your specific jurisdiction.

Multifamily lots: substantially more

On lots with existing multifamily buildings, the allowances expand significantly. Under SB 1211 (enacted in 2025), eligible multifamily properties may add up to eight detached ADUs, subject to conditions such as not exceeding the number of existing units and meeting setback and height standards. Multifamily lots also have separate provisions for converting non-livable interior space (storage rooms, attached garages) into ADUs. The precise count and conditions vary — confirm current applicability with your local jurisdiction.

What multiple units mean for MEP design

Each ADU is its own complete, independent dwelling and therefore requires its own building permit and its own MEP plan set — you cannot reuse one unit's plans for another, because each references a specific floor plan, location, climate zone, and utility configuration. Building multiple units on one property also raises capacity questions the design team must resolve:

• Electrical — can the existing service feed multiple new subpanels, or is a service upgrade or separate metering required? A load calculation for the whole property answers this.
• Plumbing — does the existing sewer lateral and water service have capacity for multiple added units, or are new connections needed?
• Gas / all-electric — local reach codes may push multiple units toward all-electric, affecting both mechanical and plumbing design.

The constraint on multiple ADUs is rarely the zoning allowance — it is usually utility capacity. Plan the electrical service and sewer/water connections for all units together, up front, rather than discovering a shortfall on the second build.

A practical approach

1. Confirm your lot type (single-family vs. multifamily) and the unit count your jurisdiction allows.
2. Have your design team evaluate total electrical, water, and sewer capacity for all proposed units.
3. Budget a separate MEP set and permit for each unit.
4. Open utility service requests early, since multiple units are more likely to trigger upgrades.

ADU unit-count rules changed materially with recent legislation and vary by jurisdiction — verify current requirements with your local building department. When you are ready to engineer each unit, our Full MEP Package covers all three disciplines per unit, and our pricing is flat by square footage. See the California ADU requirements page for more.