Title 24 for Unpermitted Work and As-Built Permits
Legalising unpermitted work means permitting it now, under the code in force when you apply: the 2025 Energy Code for applications from 1 January 2026. The Energy Commission treats a permit to legalise conditioned space added without a permit as an addition, so it is documented like new work, from drawings of what was actually built.
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Today's code applies, not the one in force when it was built
The code edition is set by the permit application date. Buildings whose permit applications are submitted on or after 1 January 2026 must comply with the 2025 Energy Code. A permit to legalise work is a new application, so work done years ago is assessed against the 2025 standards, not the code of the year it was built.
Unpermitted ADUs have extra protection under state ADU law. For an ADU built before 1 January 2020, a local agency cannot deny the permit because the unit violates building standards, unless it finds that correcting the violation is necessary for health and safety, or the building is substandard. That is Government Code Section 66311.7, as summarised in HCD's ADU Handbook. The department still decides what corrections apply.
How the Energy Code classifies the work
- An unpermitted room addition or enclosed patio. The CEC's compliance manual lists "obtaining a permit to legalize an existing, conditioned space that was previously added to a residential building without a permit" as an addition. The addition rules apply, with limits that depend on its size; see room additions.
- A garage converted without a permit. Newly conditioned space is also an addition, and solar PV is not required for additions. See garage conversion ADUs.
- Unpermitted remodelling inside existing rooms. New windows, a replaced furnace or water heater, re-insulation: these are alterations, judged on the altered components. See remodels.
Documenting what is inside the walls
For the existing house, the performance method allows default values based on the year of construction where the installed features are unknown. That does not cover the legalised space. The CEC's manual is clear on the parallel case of a conversion: existing walls that enclose newly conditioned space count as new, and verification of existing conditions applies only to altered components of the original house.
So the walls, roof and floor of the legalised space need actual values. Insulation may be established by opening a section of wall or ceiling, through the attic or crawl space, or from other evidence your building department accepts; the department decides what it needs to see. Where insulation is missing or below the requirement, it is added, or the shortfall is made up elsewhere through the performance approach.
Windows are entered from their NFRC labels where they survive. Without a rating, the code's default U-factors and SHGC values for unrated products apply, from Tables 110.6-A and 110.6-B.
Existing systems and ECC verification
Heating, cooling, ducts and water heating installed without a permit are documented as they are. Where the report relies on measures that need field verification, such as duct leakage, airflow or refrigerant charge, the CF1R is registered and an ECC-Rater tests the installed system on site. A failed test means corrections before sign-off.
One rule matters for unpermitted ADUs in particular. The California Mechanical Code does not allow return air from one dwelling unit to be discharged into another, so a unit cannot share the main house's ducted furnace. It needs its own system, and the CEC's manual notes that systems without ducts are an option.
Drawings for an after-the-fact permit
The energy report is built from drawings of the building as it exists. For the energy report, the as-built set should show:
- a dimensioned floor plan with every room labelled
- elevations showing every window and exterior door, with sizes
- wall, roof and floor construction, with insulation where known
- the heating, cooling and water heating equipment, with model numbers
If the drawings guess, so does the report. Follow your department's own checklist for legalisation; for unpermitted ADUs, the department must publish a checklist of the conditions that make a building substandard. Our guide to what plans to upload lists what we need, and plan check corrections covers questions about existing construction.
Residential reports start from $245 and ADU reports from $199, with standard delivery in 2–3 business days and unlimited revisions until you comply.
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 for the Energy Code. The edition follows the permit application date, so a permit applied for today is assessed under the 2025 standards.
Possibly. The legalised space needs actual insulation values rather than defaults, and the building department decides what evidence it accepts. Ask before cutting anything open.
No. Newly conditioned space is an addition under the Energy Code, and additions are not required to install PV.
It depends on the department. The code lets departments waive or simplify documentation for additions under 300 square feet that need no field verification, so ask before ordering.