Any project that adds heated or cooled floor area to a home is an addition under the California Energy Code, and it needs a Title 24 report (CF1R). We prepare it for the 2025 Energy Code, which applies to permits applied for on or after January 1, 2026.
What counts as an addition?
The CEC defines an addition as any change that increases conditioned floor area and conditioned volume. That includes:
- A new room or second story.
- An attached ADU.
- Turning a garage, porch or storage room into living space.
Additions follow Section 150.2(a).
Which rules depend on the size of the addition?
The CEC's 2025 compliance manual lists prescriptive allowances by size:
| Addition size | Max glazing (prescriptive) | QII | Rafter roof insulation |
|---|---|---|---|
| Up to 400 sq ft | 75 sq ft or 30% of floor area, whichever is greater | Does not apply | R-22 |
| Over 400, up to 700 sq ft | 120 sq ft or 25% of floor area | Does not apply | R-22 |
| Over 700 sq ft | 175 sq ft or 20% of floor area, whichever is greater | Applies | Not listed as an allowance |
West-facing glass is also capped in climate zones 2, 4 and 6 through 15. For additions of 700 square feet or less, the cap is 60 square feet. Over 700 square feet, it is 70 square feet or 5% of floor area, whichever is greater.
Other exceptions that apply to every addition:
- 300 square feet or less: no cool roof product required.
- 1,000 square feet or less: no whole-house fan required.
- Solar PV: not required for additions.
What about heating and cooling?
Extending existing ducts. The manual says an existing system extended to serve the addition must meet the duct insulation and duct leakage requirements. If existing equipment serves the addition, its refrigerant charge and airflow tests are not required.
New system for the addition. It must meet all the space conditioning rules for a new home. That includes refrigerant charge verification in all climate zones for heat pumps, and in zones 2 and 8 through 15 for air conditioners. Fan airflow and watt draw testing applies in all climate zones.
Those tests are done by an independent ECC (HERS) rater.
How is the addition modeled?
The CEC manual describes three approaches:
- Addition alone. Only the addition is modeled. It needs little information about the house. It also gets less window allowance. A 400 square foot addition is limited to 20% glazing this way, instead of 30%.
- Existing + addition + alteration. The whole house is modeled. Upgrades to the existing house can offset the addition. Nothing in the existing house has to be changed. This approach needs plans and data for the existing house.
- Existing + addition as new construction. Used when the changes to the house are extensive. Everything must meet current code, so it is harder to pass.
If you are also altering the house, prescriptive projects use a CF1R-ADD form for the addition and a CF1R-ALT form for the alterations.
What about the water heater?
If you add a water heater to serve an addition of 500 square feet or less, an electric water heater with point-of-use piping is allowed prescriptively.
What do I send to get started?
- Floor plan of the existing house and the addition, with dimensions
- Elevations with window and door sizes
- Wall and roof details for the new work
- Heating, cooling and water heating plans for the addition
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Frequently asked questions
Does a home addition need a Title 24 report?
Yes. Any change that adds conditioned floor area and volume is an addition under the Energy Code and must comply with Section 150.2(a). Most additions use a prescriptive CF1R-ADD form or a performance CF1R-PRF report.
Does an addition need solar panels?
No. The CEC compliance manual says PV requirements do not apply to additions or alterations.
Can my existing furnace serve the addition?
Yes. If you extend existing ducts, they must meet duct insulation and duct leakage requirements. If you install a new system for the addition, it must meet new-home requirements, including refrigerant charge verification.
How much window area can an addition have?
Under the prescriptive rules it depends on size. Up to 400 square feet: 75 square feet of glazing or 30% of floor area, whichever is greater. Over 400 up to 700: 120 square feet or 25%. Over 700: 175 square feet or 20%, whichever is greater.
Related
Sources
- energy.ca.gov/filebrowser/download/8641?fid=8641
- energy.ca.gov/sites/default/files/2026-07/CEC-400-2025-010-F.pdf
- energy.ca.gov/filebrowser/download/8634?fid=8634
- energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center-6/2025
- energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/2025-building-energy-efficiency