Who is legally allowed to prepare MEP plans for an ADU in California?

For most wood-frame ADUs, California law does not require the MEP plans to be prepared by a licensed architect or engineer. Business and Professions Code sections 5537 and 6737.1 let any person prepare plans for wood-frame single-family dwellings, small multiple dwellings and appurtenant structures up to two stories and a basement. Your building department can still require a licensed professional in specific situations, so confirm before you hire.

What the exemptions say

The same exemption appears in the Architects Practice Act (B&P 5537) and the Professional Engineers Act (B&P 6737.1). It covers:

• Single-family dwellings of wood-frame construction not more than two stories and basement in height.
• Multiple dwellings of no more than four units, with the same construction and height limits.
• Garages or other appurtenant structures of wood-frame construction within the same height limit.

The California Architects Board's guide for building officials adds two details that matter for ADUs. On a lot that already has a house, an unlicensed person can design at most three additional units. And the exemption refers only to wood framing, so a metal-framed structure does not qualify.

When a licensed professional comes back in

• Unconventional framing. If any portion deviates from the conventional wood-frame requirements in Title 24, the building official must require that portion to be prepared and stamped by a licensed engineer or architect.
• Local judgment. The Architects Board says building officials may require part or all of a structure to be designed by an architect or engineer when they see an undue risk to public safety.
• Local policy. Some departments publish their own rules. Los Angeles, for example, issues a policy bulletin that lists these exemptions and the project types that need a licensed engineer's or architect's signature.

Who else may prepare them

• Architects. The Architects Board states that architects may prepare, stamp and sign mechanical, electrical and plumbing drawings.
• Engineers. Licensed electrical and mechanical engineers may, within their branch. Under B&P 6704, only licensed or specifically exempt people may practice civil, electrical or mechanical engineering.
• Contractors. Licensed contractors may design the electrical or mechanical systems they will install themselves (B&P 6737.3).

Whoever prepares plans for someone else must sign them (B&P 5536.1).

What this means for your MEP plans

Being exempt under state law is not the same as being accepted at your city's counter. The practical question is what your building department asks for on your project. MEP Plans USA prepares MEP plans for California ADUs and checks the stamp expectations for your city; where a jurisdiction requires a Professional Engineer's stamp, it is available as a separately quoted add-on. See whether MEP plans need a PE stamp and the California ADU permit guide. This is general information, not legal advice. Rules vary, so confirm with your building department.

Sources: cab.ca.gov, bpelsg.ca.gov, cab.ca.gov, bpelsg.ca.gov, dbs.lacity.gov.