Title 24 for Legalizing an Old Garage Conversion
An old garage conversion is classified as an addition when you legalize it, even though the room is finished. The department decides how compliance is shown, the existing walls count as new, and any ducts extended from the house or new equipment are tested on the finished work.
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Finished room, new-work rules
The compliance manual lists permitting previously unpermitted conditioned space as an addition, and converting a garage into living space is on the same list. The Commission's ADU guidance adds that the department decides how compliance is demonstrated and whether an ADU is newly constructed or an addition. Solar is not required for an addition.
What is behind the old garage walls
Existing walls around newly conditioned space count as new, so there is no credit for verifying them. Where the siding stays, the prescriptive wall value is R-15 in 2x4 framing or R-21 in 2x6. The infilled door opening is new framing and is shown as a wall, or as glass or a door if one was installed. A garage slab needs no perimeter insulation in zones 1 to 15. Ask what evidence of insulation the department accepts, such as an opened wall bay.
Tests on finished work
- Extended ducts. If the room runs off the house furnace's ducts, the combined system tests at 10 percent leakage or 7 percent to outside. Where neither can be met, an ECC-Rater smoke-tests the sealed ducts and visually inspects every accessible connection, boot and plenum joint (RA3.1.4.3.6 and RA3.1.4.3.7). Ask the department what it treats as accessible.
- A unit with its own kitchen. A central-return furnace cannot serve an ADU, because the Mechanical Code bars discharging return air into another dwelling unit. A mini-split or multi-split may need ECC-Rater testing, including refrigerant charge, and a vented range hood is verified.
The pre-2020 protection
One extra argument exists for a unit: an ADU or junior ADU built before 1 January 2020 cannot be refused a permit for building-standards violations unless the agency finds correction necessary for health and safety, or the building is substandard (Government Code 66311.7). HCD words it for ADUs and JADUs only.
Edition and drawings are on unpermitted work, classification is on legalizing unpermitted construction, and the checklist for the unit is on garage conversion ADUs. A room above a garage is a bonus room. See ADU Title 24 reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
Not by itself. The permit application is judged against the code in force when it is submitted, and the department decides how the space is classified.
That depends on what the department accepts as evidence of the insulation. Existing walls around newly conditioned space count as new, so no credit is available for verifying them.
Explore Existing Buildings
- Title 24 for Unpermitted Work and As-Built Permits
- Buying a Home With an Unpermitted Addition or Garage Conversion: Where Title 24 Fits
- Expired Permit: Which Title 24 Code Applies?
- An Open Permit That Was Never Finaled: What the Energy Paperwork Still Needs
- Can You Reuse a Title 24 Report?
View all Existing Buildings guides → · Permits and Compliance · Title 24 guide