Can my electrician or HVAC contractor draw the MEP plans for my ADU?

Often, yes, for the systems they will install. Business and Professions Code section 6737.3 lets a licensed contractor design electrical or mechanical systems for work that contractor will perform and supervise within its license classification. Most wood-frame ADUs also fall under the general design exemption in B&P 5537 and 6737.1, so a contractor can usually prepare those plans just as any other designer could.

What the law allows

• Design for their own installation. Under B&P 6737.3, a contractor in the business of installing electrical or mechanical systems may design those systems in accordance with applicable codes and standards for work it performs and supervises, and may prepare shop and field drawings for work it has contracted to do.
• Not for someone else's installation. The same section states that nothing in it implies a contractor may design work to be installed by another person.
• Exempt buildings. The California Architects Board's guide says a contractor may design whatever an unlicensed person may design under B&P 5537. For buildings outside that exemption, contractors who do not install and supervise the systems must have an architect or engineer design them.
• License classification. The Contractors State License Board lists C-10 (Electrical), C-20 (Warm-Air Heating, Ventilating and Air-Conditioning) and C-36 (Plumbing). The design allowance follows the classification the contractor holds.

Trade-offs to weigh

• Coordination. With separate electrical, HVAC and plumbing drawings, someone still has to confirm the panel load includes the heat pump and water heater, the condensate drain has a route, and the equipment matches the Title 24 report.
• Bidding. Plans drawn by one contractor around its own equipment can make it harder to compare bids from others.
• Contractor changes. If the contractor who designed a system leaves the project, ask how the replacement will handle any plan revisions before work continues.
• Plan check content. The city expects the same items whoever draws the sheets: load calculations, equipment schedules, fixture counts, venting and code notes. Sheets missing those items can come back with corrections.

Questions to ask before you agree

1. Will the plans include everything your city's submittal checklist asks for, including calculations?
2. Who answers plan check corrections, and is that part of the price of the job?
3. Who updates the Title 24 report if equipment changes?

What this means for your MEP plans

Contractor-prepared drawings can work, especially for a single trade. If you want one coordinated set that any licensed installer can bid and build from, independent MEP plans keep the design separate from the installer. MEP Plans USA prepares coordinated mechanical, electrical and plumbing sheets for California ADUs, delivered as PDFs, with a standard turnaround of 5 business days and two revisions plus city plan-check corrections included. Compare options in choosing an MEP plan provider and see the Full MEP Package. Confirm local acceptance with your building department; this is not legal advice.

Sources: bpelsg.ca.gov, cab.ca.gov, cab.ca.gov, cslb.ca.gov.