What plans are needed for a garage conversion?

A California garage-to-ADU conversion typically needs a coordinated set of architectural, structural (where required), mechanical, electrical, and plumbing (MEP) plans, plus a registered Title 24 energy compliance document. The conversion turns a non-habitable storage space into a legal dwelling, and the building department reviews every system that makes that space safe to live in.

The full plan set for a garage conversion

Converting a garage means proving the new living space meets habitability code — insulation, egress, ceiling height, light and ventilation — and that its active systems are designed to residential standards. A typical permit package includes:

• Architectural plans — floor plan, site plan, and elevations showing the new layout, closing of the garage door opening, egress windows, and finished room arrangement. These are the foundation the MEP engineer works from.
• Structural details — when framing the old door opening, modifying the slab, or altering the roof, structural sheets or details may be required.
• Mechanical (M) plans — a residential heating, cooling, and ventilation design, almost always a mini-split heat pump plus whole-building ventilation per ASHRAE 62.2.
• Electrical (E) plans — a new circuit layout, panel/subpanel schedule, and load calculation sized for an independent dwelling.
• Plumbing (P) plans — a DWV and water-supply design for the new kitchen and bathroom, since garages rarely have any plumbing.
• Title 24 CF1R — the registered energy compliance certificate, prepared under alteration rules for conversions.

Why a garage starts further behind than it looks

Homeowners often assume an existing structure shortcuts the process. It rarely does. A garage is built and wired for non-habitable, non-residential use: bare or minimal insulation, a concrete slab with no below-grade plumbing, a couple of general-purpose circuits, and ventilation that depended on the gap around the door. Making it habitable means engineering each system close to new-construction standards — which is exactly why the plan set is so complete.

Checklist before you order plans

• Completed architectural floor plan, site plan, and elevations
• Project address (for climate zone and code confirmation)
• Existing main-panel size, if known
• Preferred HVAC type, or "unsure"
• Any special requests: EV charger, panel upgrade, specific appliances

How the disciplines fit together

The reason these plans are issued as a coordinated set rather than independent documents is that they constantly reference one another. The mini-split shown on the mechanical sheet needs a dedicated circuit reflected in the electrical load calculation; the water heater on the plumbing sheet has an efficiency rating that must match the Title 24 CF1R; the bathroom exhaust fan appears on both the mechanical and electrical sheets. When separate vendors prepare these pieces in isolation, the mismatches surface during plan check as corrections. A single team working from the same architectural plans keeps the equipment schedules, circuit assignments, and energy modeling consistent — which is the difference between a clean first review and several correction rounds.

What is and isn't included

MEP plans cover the active engineered systems — ductwork and HVAC equipment, circuits and panels, pipes and fixtures. They do not cover the architectural and structural scope: framing the closed door opening, insulation assemblies, egress windows, exterior cladding, and ceiling-height work. Those belong on the architectural and structural sheets, prepared by your designer or architect. Knowing the split up front helps you assemble a complete submittal package rather than discovering a missing sheet mid-review.

Requirements vary by jurisdiction — confirm the exact submittal list with your local building department. If you want one coordinated team handling all three disciplines plus Title 24, our Full MEP Package starts at $1,495, and you can start your order with just your architectural plans. See how it works for the step-by-step.