01“ADU” does not identify the entire energy-code scope
California ADUs are subject to the Energy Code, but the word ADU does not identify one universal compliance path. A newly built detached dwelling, a garage becoming conditioned space and a room already inside the conditioned house can follow different requirements. Before requesting a CF1R, establish the building’s previous condition, proposed dwelling boundary and affected systems. That decision is more useful than searching for a generic “ADU exemption.”
For current planning, the 2025 California Energy Code generally applies to permit applications recorded on or after January 1, 2026. Earlier valid applications may use the 2022 edition; the AHJ confirms its recorded application date and treatment of later changes. Construction start, a drawing date and the date someone orders a report are not substitutes for that application record.
This guide concerns Title 24 Part 6 energy documentation. CALGreen is Part 11, and planning eligibility, zoning, structural work and other building-code reviews are separate. Use the CEC’s ADU FAQs for statewide educational guidance, then confirm the actual permit scope with the responsible designers and reviewing department. No local ordinance or approval outcome is assumed here.
CEC 2025 ADU FAQsConfirm 2022 versus 2025 by application date
02Classification decision tree
Describe the physical work before selecting a form or modeling boundary. The CEC distinguishes newly constructed buildings, additions and alterations; keeping that distinction visible prevents a misleadingly simple quote from becoming the wrong permit package.
- +New detached building: a structure constructed as a new dwelling is treated as newly constructed single-family for Energy Code purposes. It must address mandatory requirements and the applicable prescriptive or performance route; its small size alone does not remove those obligations.
- +Attached new ADU: show the common wall, floor or ceiling and the newly conditioned area and volume. The CEC treats attached ADUs as additions, with the applicable Section 150.2(a) pathway rather than automatically treating them as new detached buildings.
- +Unconditioned garage conversion: a previously unconditioned garage becoming conditioned space is an Energy Code addition, even when its footprint does not grow. The same conditioning-history question matters for a detached existing garage; detached does not always mean newly constructed.
- +Previously conditioned conversion: converting existing conditioned space into an ADU or JADU is an alteration. Applicable changed components and systems follow Section 150.2(b); do not model it as newly added conditioned area without checking the history.
- +Mixed project: mark conversion, new floor area and changes to the original home separately. Supply prior permitted records where available. If existing work is undocumented, ask the AHJ how it must demonstrate compliance rather than assuming an old use or heater establishes a permitted conditioned building.
CEC ADU resource hub and older-edition materialsProject-specific ADU and garage-conversion report support
03A JADU is a defined Energy Code term, not just a small ADU
The CEC’s 2025 FAQs describe the Section 100.1 Energy Code definition of a junior accessory dwelling unit: no more than 500 square feet, entirely within a newly constructed or existing single-family building, with a kitchen, a separate entrance and an interior entry to the main living area. Sanitation may be separate or shared. Read the full definition rather than using the area limit alone.
That definition does not establish planning eligibility or settle every system requirement. A JADU inside a new building is different from work within an existing dwelling. For an existing building, identify whether the project adds conditioned area or changes already conditioned space and which components are affected. The energy-documentation scope follows those facts; the designer and AHJ resolve the applicable classification.
04Choose prescriptive or performance after establishing the scope
Prescriptive compliance follows the applicable component and system provisions for the classified work. Performance compliance evaluates an eligible proposed design using approved software for the governing edition. Mandatory measures still apply. A performance model is not permission to ignore ventilation, installation requirements or a required verification simply because a calculation passes.
Ask what decision the model should answer. A detached design may need comparison of glazing, envelope and equipment options before the permit package is fixed. An addition/conversion needs the appropriate Section 150.2 boundary and evidence. If a straightforward prescriptive approach fits the design, an extensive option study may add little value; if important design choices remain open, preliminary modeling can make those choices explicit.
Separate preliminary assumptions from final selections. Record unresolved window performance, assemblies and systems before pricing a final run. The permit-ready compliance output should match the coordinated drawing revision; it is not the same deliverable as a quick option comparison.
Energy modeling and controlled option studiesPrescriptive versus performance decisionsAddition-alone versus existing-plus-addition boundaries
05ADU intake checklist
Send existing and proposed information together. A well-labeled packet lets the preparer identify the correct scope instead of guessing from a rendered exterior or an isolated floor plan. Mark unknown values as unknown; do not copy another project’s specifications.
- +Project record: address, reviewing AHJ, application date if known, permit identifiers, prior reports and the project type: detached new building, attached addition, conversion or a combination.
- +Plans and areas: site orientation, dimensioned existing/proposed plans, elevations and sections; conditioned area and volume, dwelling count in the requested scope, and clear boundaries between the ADU and original home.
- +Envelope: window and glazed-door sizes, orientation, U-factor and SHGC from the selected schedule/product data; roof, wall, slab and floor assemblies, insulation intentions and retained versus replaced components.
- +HVAC and ventilation: the proposed system and equipment information, areas served and any affected existing system. Identify a proposed extension separately from a dedicated system; do not assume that sharing a meter makes shared air distribution acceptable.
- +Domestic hot water and other coordination: water-heating equipment and distribution intentions, any claimed PV/battery provisions, electrical-readiness questions and the responsible systems designer. Avoid treating a generic equipment description as a final selection.
- +Submission history: complete plan-check comments, the actual reviewed sheets and a change log for revisions. Provide readable PDF plans; include supporting DWG or ZIP files where useful and keep sheet dates and identifiers consistent.
Complete what-to-send checklist with file-preparation advice
06Worked example: detached new dwelling versus garage conversion
ILLUSTRATIVE ONLY — not a client case, approved design or compliance result. Option A is a proposed 580 sq ft detached ADU built from the ground up. Option B converts a 580 sq ft existing unconditioned garage. The matching area makes the difference easier to see: it does not establish a threshold, exemption or common permit treatment.
For A, the team starts with newly constructed single-family requirements, mandatory measures and a prescriptive/performance choice. It coordinates envelope, HVAC, domestic hot water, ventilation and the applicable PV questions before finalizing the CF1R. For B, the team documents prior unconditioned use and evaluates the addition pathway under Section 150.2(a), with existing assemblies and new conditioning clearly identified.
The initial packet contains floor plans and a window schedule, but the garage wall assembly is unknown and both options say only “mini-split” for HVAC. The useful next step is not to assume both models are identical. The designer supplies the missing assembly evidence and system information; the preparer records any provisional assumptions and identifies which decisions prevent a final package.
Once those decisions are coordinated, the relevant compliance documents match the drawings. Installation and required ECC verification follow their own stages. No pass/fail result, solar exemption, local review deadline or mechanical-design approval is implied by this example.
07PV, existing systems and verification need scope-specific answers
The CEC’s 2025 ADU FAQs state that newly constructed detached ADUs need newly installed PV for the prescriptive requirement unless an applicable exception applies. Existing PV alone is not automatically the answer; the FAQs discuss adding new modules to an existing system. They also say attached ADUs, treated as additions, do not require PV under that new-construction requirement. Confirm the actual scope and exceptions instead of converting that statement into a universal exemption.
Do not assume that an existing furnace can simply extend into a separate dwelling. The CEC specifically addresses restrictions on using an existing dwelling’s ducted forced-air system to serve an ADU. A mechanical designer must resolve the actual system and ventilation approach. An energy report is not that design service.
For current-cycle residential work, use Energy Code Compliance, or ECC, verification terminology. HERS may appear in older-cycle documents or legacy searches. Read the actual required measures: a mini-split label does not by itself establish the complete verification list or eliminate it. Arrange the qualified participants and needed access before relying on construction-stage signoffs.
08From design report to construction records
Where the single-family form family applies, CF1R records design compliance, CF2R records installation and CF3R records required ECC verification. Confirm the correct family for the building rather than treating every residential classification as identical. Required registration and responsible declarations must be addressed through the applicable project/provider process; a draft model printout is not necessarily the registered submittal copy.
Title 24 Lab prepares design-phase documentation and coordinates handoffs; it does not claim to perform installer certification or field testing. Keep the accepted plan revision, equipment substitutions, applicable installation records and verification records together. If a reviewer identifies inconsistent features, respond comment by comment and coordinate drawings with the compliance package.
CF1R preparation and CF2R/CF3R responsibilitiesPlan-check corrections and coordinated resubmittals
09Six ADU energy-documentation questions
Use these answers to prepare for scope review, not to self-approve the project.
Does every ADU need the same CF1R package?
No. ADUs are subject to energy requirements, but building classification, existing conditioning, proposed work and edition determine the documentation. Confirm the permit’s required forms with the preparer and AHJ. A detached new building and an unconditioned garage conversion should not be assumed to follow identical paths.
Is a garage conversion an addition even without new floor area?
For Energy Code purposes, converting unconditioned space increases conditioned floor area and volume and is treated as an addition. Work inside already conditioned space is different. Document the prior condition and ask the AHJ about unclear or unpermitted history rather than inferring status from finishes or equipment alone.
Does a JADU automatically avoid energy documentation?
No. The Energy Code defines JADUs, but the applicable requirements depend on whether the work is in a new building, an addition or an alteration and which components change. The size limit alone is not an energy exemption or a determination of local planning eligibility.
Will the ADU need solar panels?
Newly constructed detached ADUs generally face the prescriptive PV requirement unless an applicable exception applies. The CEC distinguishes attached additions and discusses new modules added to existing systems. Supply the actual project and proposed PV arrangement; this guide does not grant a universal exemption or design the PV system.
Which code edition and verification terminology should I use?
Confirm the AHJ-recorded application date. Applications on or after January 1, 2026 generally use the 2025 Energy Code and ECC terminology. Earlier valid applications may use 2022 documents with legacy HERS language. Ask about later application changes instead of choosing an edition from the construction date.
Are field testing and permit fees included with report preparation?
No. Review the published scope and exclusions. ECC field testing, acceptance testing, registry fees, CALGreen and AHJ permit fees are separate. The responsible installer and qualified verifier complete their applicable construction-stage records; purchasing a design report does not perform those tasks.
10Next step: identify the scope before requesting a report
Use the existing residential square-footage pricing and dwelling count for the requested documentation scope, not an invented ADU-only menu. Send the existing/proposed plans and unresolved decisions with your quote request. Intake is scope review, not payment, production acceptance or permit approval.
Educational information, not legal advice. The AHJ determines permit requirements and local amendments; responsible designers determine project-specific technical solutions. Title 24 Lab remains a provisional brand, not a claim of credentials or local offices.
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