Does a manufactured home ADU need a Title 24 energy report or solar panels?

Generally no for the home itself. The California Energy Commission says manufactured homes are governed by Title 25 rather than the Title 24 Energy Code, and HCD's ADU Handbook notes that manufactured homes are excluded from the Energy Code's solar requirement for newly constructed detached ADUs. The site work that connects the home to your property, including the foundation system, electrical service, water, and sewer, still goes through your local building department.

What counts as a manufactured home

Under Health and Safety Code section 18007, a manufactured home was built on or after June 15, 1976, on a permanent chassis; is transportable in one or more sections (at least 8 body feet wide or 40 body feet long in traveling mode, or at least 320 square feet when set up); and is designed as a single-family dwelling with or without a foundation. It is built to federal HUD standards and carries a HUD label. State ADU law expressly includes manufactured homes in the definition of an ADU.

Not the same as modular or factory-built

A modular unit approved under California's Factory-Built Housing program is a different product, built to the California Building Standards Code, and the CEC says factory-built homes must comply with Title 24, Part 6. If your prefab ADU carries an HCD factory-built insignia instead of a HUD label, expect Title 24 compliance documents and, for a new detached unit, solar PV unless an exception applies.

Who permits what

• The home: federal standards and HCD's Title 25 regulations govern its construction, including the plumbing, heating, air conditioning, and electrical systems built into it. The CEC adds that additions to a manufactured home also fall under Title 25.
• The installation: to install a manufactured home on a foundation system on your lot, Health and Safety Code section 18551 requires a building permit from the local enforcement agency, which inspects the installation and issues the certificate of occupancy.
• The ADU approval: your city or county still reviews the ADU under State ADU Law, including setbacks and other objective standards.

What it means for your MEP plans

• Electrical: the home arrives with its own panel. Site plans cover the feeder or service to it, sized by a load calculation that includes your existing house, plus grounding and trench routes.
• Plumbing: plans show the water service, the sewer connection to your existing lateral or a new one, and any gas line if the home uses gas.
• Mechanical: usually limited to items outside the home's factory scope, such as the outdoor condenser location.
• Title 24: not required for the home under the CEC's guidance; confirm how your building department wants that documented at intake so the application is not held up.

Confirm the label before you plan permits, because "prefab" is used loosely and the two paths are very different. See the California ADU requirements guide, subpanels for detached ADUs, and ADU sewer connections.

Sources: energy.ca.gov, energy.ca.gov, hcd.ca.gov, hcd.ca.gov.