What electrical work is specific to garage conversions vs. new detached ADUs?

The code requirements for the finished dwelling are the same — both need a properly sized panel, GFCI/AFCI protection, dedicated circuits, smoke/CO alarms, and EV provisions — but how you get there differs sharply. A garage conversion adapts and corrects existing wiring, while a new detached ADU is a clean, ground-up design with its own grounding and feeder. Each path has its own typical electrical scope and its own common pitfalls.

Garage conversions — adapt, correct, and bring up to code

A garage was never wired as living quarters, so a conversion is largely about transforming and supplementing what's there:

• Existing wiring is usually inadequate. A garage often has just a couple of receptacles and a light on one circuit — nowhere near the circuit count a dwelling needs. New dedicated circuits for kitchen, laundry, bath, HVAC, and appliances get added.
• GFCI and AFCI retrofits. Old garage receptacles frequently lack GFCI, and habitable-room AFCI didn't exist when the space was built — both must be brought current.
• Existing subpanel or feeder may need upsizing. If the garage has a small subpanel, the load calc often shows it can't carry a full dwelling load.
• Smoke/CO alarms. The new sleeping room and each story need full alarm coverage, interconnected and hardwired — a routine legalization correction.
• Verifying concealed work. For unpermitted conversions, existing wiring is suspect until inspected — double-tapped breakers, reversed polarity, and improper splices are common finds.

New detached ADUs — clean design, but more infrastructure

A ground-up detached unit has no legacy wiring to correct, but it carries infrastructure a conversion attached to the house may not:

• A feeder run from the main house panel to the detached subpanel — typically four conductors in underground conduit, with voltage drop driving conductor size on long runs.
• Its own grounding electrode system. A detached structure generally needs its own ground rods (or a Ufer/concrete-encased electrode) bonded to the subpanel, in addition to the equipment ground in the feeder.
• Strict four-wire subpanel rules — isolated (floating) neutral, bonded ground, and no neutral-ground bond downstream of the main.
• Full solar and ESS-ready provisions. Newly constructed detached ADUs are the units most likely to trigger the solar PV mandate and ESS-ready requirements.

Quick comparison

Requirements vary by jurisdiction and code cycle — solar applicability, alarm rules, and what existing wiring may be reused differ between new construction and conversions. Confirm with your local building department.

Our electrical plans are tailored to whichever path you're on, and two revisions plus city corrections are included. See the ADU electrical guide for more, or place an order from $995.