A garage conversion is an addition under the California Energy Code, because it turns unconditioned space into conditioned space. We prepare the Title 24 report (CF1R) that shows your converted garage meets the 2025 Energy Code.
Why is a garage conversion an addition?
The CEC defines an addition as any change that increases conditioned floor area and conditioned volume. A garage is not heated or cooled. Once it becomes living space, it is. The CEC's ADU FAQ says this is true whether the garage is attached to the house or detached. Additions follow Section 150.2(a).
What does that mean for my project?
No solar requirement. The CEC's compliance manual says PV requirements do not apply to additions or alterations.
Existing walls count as new. The CEC says walls around newly conditioned space are treated as new for the Energy Code. They must meet the insulation rules for an addition. You cannot take a credit for them as "existing."
2x6 walls can stay as they are outside. For prescriptive compliance, existing 2x6 walls can be insulated with R-21 in the cavity. Continuous insulation is not required for those walls.
QII depends on size.
- 700 square feet or less: the prescriptive QII inspection does not apply. A rater must still verify it if the report takes QII as a credit.
- Over 700 square feet: QII applies. For a converted garage, it does not include header insulation, or air sealing if the existing air barrier stays in place.
Cool roof only in some zones. Additions over 300 square feet in climate zones 10 through 15 must meet cool roof rules for steep-sloped roofs. Low-sloped roofs are covered in zones 13 and 15. Many Los Angeles County cities, such as Long Beach, Torrance and Pasadena, are in zones 6, 8 or 9, where the steep-slope rule does not apply.
Small-space water heating. If the conversion is 500 square feet or less and gets its own water heater, an electric water heater with point-of-use piping is allowed prescriptively.
What about heating and cooling?
Most garage conversions use a ductless mini-split. The CEC says mini-splits can trigger ECC (HERS) rater testing, including refrigerant charge in all climate zones. If you extend the main house's existing ducts instead, the manual says the extended system must meet duct insulation and duct leakage requirements.
If the conversion becomes a separate ADU, the existing house's furnace cannot serve both. The CEC notes the California Mechanical Code does not allow return air from one dwelling to be sent into another.
Addition alone, or the whole house?
The CEC manual describes two common ways to model an addition:
- Addition alone. Only the converted garage is modeled. It is simpler and needs little information about the house.
- Existing + addition + alteration. The whole house is modeled. This can allow more window area and lets upgrades to the house offset the addition. It needs plans and data for the existing house.
We pick the approach that fits your plans and tell you why.
What do I send to get started?
- Floor plan of the garage with dimensions
- Elevations showing windows and doors
- Wall, roof and slab details, if drawn
- Heating, cooling and water heating choices, if known
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Frequently asked questions
Is a garage conversion an addition or an alteration under Title 24?
An addition. The CEC says converting unconditioned space, like a garage, into conditioned space is an addition, whether the garage is attached or detached. It follows Section 150.2(a).
Does a garage conversion ADU need solar panels?
No. The CEC compliance manual says PV requirements do not apply to additions or alterations.
Do I have to remove the siding to add continuous insulation?
Not for prescriptive compliance with existing 2x6 walls. The CEC says those walls can be insulated with R-21 in the cavity, and continuous insulation is not required for them.
Does a garage conversion need QII?
Not if it is 700 square feet or less and complies prescriptively. Over 700 square feet, QII applies, but for a converted garage it excludes header insulation and air sealing where the existing air barrier stays in place.