What are MEP Plans?

MEP plans are the engineering drawings that show how a building's Mechanical, Electrical, and Plumbing systems will be designed, sized, installed, and coordinated. For a California ADU, they are the documents a plan checker uses to confirm your heating and cooling, power and lighting, and water and waste systems are safe and code-compliant before a permit is issued.

The three disciplines explained

Each letter is a full engineering discipline with its own set of plan sheets, labeled M-1/M-2, E-1/E-2, and P-1/P-2:

• Mechanical (M) — heating, cooling, and ventilation. This covers the HVAC system (most commonly a ductless mini-split heat pump in California ADUs), heat load calculations, equipment schedules, bathroom and kitchen exhaust, and the whole-building ventilation required by ASHRAE 62.2 and Title 24.
• Electrical (E) — power and lighting. This covers the electrical floor plan, panel schedule, NEC/CEC load calculations, dedicated appliance and EV circuits, GFCI and AFCI protection, and smoke/CO detector locations.
• Plumbing (P) — water, waste, and gas. This covers water supply routing and sizing, the drain-waste-vent (DWV) system, the water heater, fixture schedules confirming CALGreen low-flow compliance, and gas piping where allowed.

What a permit-ready set actually contains

A complete California ADU MEP set is more than a floor plan with symbols on it. It includes a cover sheet citing the applicable codes (CBC, CEC, CPC, CMC, and the current Title 24 energy code), formal calculations (Manual J heat load and NEC Article 220 electrical load), equipment schedules listing make, model, capacity, and efficiency ratings, and all the notes and callouts a reviewer expects. These are construction documents, not preliminary sketches.

How MEP plans differ from architectural plans

It's a common point of confusion. Architectural plans show what the building looks like and how it is laid out — room dimensions, window and door locations, exterior elevations. MEP plans show only the engineering systems inside: the ductwork, circuits, pipes, and equipment schedules. The two are separate documents that must be coordinated with each other, which is why an MEP engineer works from your completed architectural drawings rather than the other way around. Structural plans are a third, separate discipline covering foundations, framing, and load-bearing elements.

Why they matter for your project

Inspectors and building departments cannot verify code compliance on systems they cannot see documented. Well-prepared MEP plans help ensure the ADU is safe, energy efficient, and capable of supporting a full household — and they are the single most effective way to avoid the plan check corrections that delay permits. They also serve as the reference document at every construction inspection, from rough-in (before the walls close) through final, so accurate plans translate directly into clean inspections. Each discipline is covered in depth on its own page: see Mechanical Plans, Electrical Plans, and Plumbing Plans.

Requirements vary by jurisdiction — confirm the specifics for your project with your local building department. If you want the engineering handled end-to-end, our Full MEP Package delivers all three disciplines as one coordinated, permit-ready set.