Does California require separate mechanical permits for ADUs?

An ADU's mechanical work nearly always requires permitting, but whether it is issued as a separate mechanical permit or rolled into the combination building permit depends on your jurisdiction. For a new ADU, the HVAC and ventilation are typically reviewed and inspected under the same combination permit as the building, electrical, and plumbing scopes — but the mechanical scope still has to be shown, plan-checked, and inspected on its own merits.

How permitting is usually structured

• New ADU construction: Most California cities issue a single combination building permit that covers building, mechanical, electrical, and plumbing (the "MEP" trades) together. The mechanical plans are part of that submittal and receive their own plan-check review and field inspections.
• Standalone HVAC work in an existing unit: Replacing or adding HVAC outside of a larger project often pulls a dedicated mechanical permit.
• Larger or phased projects: Some jurisdictions break the trades into separate trade permits issued to the licensed contractor performing each scope.

The practical point is the same in every case: the mechanical design must be documented and approved. A combination permit doesn't reduce what the mechanical plans have to show.

What the mechanical review checks

Regardless of how the permit is packaged, the reviewer verifies the same items:

1. A Manual J heat load calculation supporting the equipment sizing.
2. A complete equipment schedule (make, model, BTU/hr, efficiency) meeting Title 24 minimums.
3. ASHRAE 62.2 whole-building ventilation, designed and documented separately from heating and cooling.
4. Local exhaust — bath fans and a kitchen hood ducted to the exterior.
5. Outdoor condenser location with property-line and window setbacks.
6. Refrigerant line-set or duct routing shown.
7. Condensate drainage routing.

Why it matters who pulls the permit

In many jurisdictions a licensed mechanical (C-20 HVAC) contractor pulls the mechanical permit and is responsible for the installation matching the approved plans. Homeowners acting as owner-builder may pull permits themselves where allowed, but the inspection standard is identical. Either way, the work must be inspected and the permit closed with a passed final — which also matters because most heat pump rebate programs require a closed permit before they release funds.

Whether mechanical is a separate permit or part of a combination permit, the mechanical plans still must be complete. Bundling them with a Title 24 report keeps the equipment on the drawings consistent with the energy calcs and avoids the most common mismatch correction.

Permit structures, fees, and which trades are combined vary significantly by jurisdiction — confirm the exact requirements with your local building department before you submit. Our mechanical plans are prepared to satisfy mechanical plan check whether issued standalone or as part of a combination permit, and the Full MEP package keeps all three trades coordinated. See how it works or start your order.