California Title 24 Energy Modeling & Option Studies

Who benefits from a project-specific model?

Start with the decision you need to make, not a request for a generic “passing report.” For new construction, early modeling can compare glazing, assemblies and equipment while drawings can still change. For additions and remodels, first establish the affected area, systems and existing-building evidence. A model is useful when a permitted performance approach can answer a real design question; it is not automatically necessary for every small alteration.

For ADUs and garage conversions, establish whether the work creates a new building, newly conditioned space or an alteration before choosing boundaries. For commercial tenant improvements and NRCC documentation, identify affected envelope, lighting and mechanical scopes with the responsible designers. Not every tenant improvement needs a whole-building performance study. If the plans, scope or equipment decisions are too unsettled, resolve those first rather than paying for repeated runs that answer different questions.

Prescriptive versus performance: choose a useful path

Prescriptive compliance documents the applicable specified requirements for the project. It may fit a straightforward design that can meet those requirements without an option study. Performance compliance uses approved software to compare a proposed design with its applicable standard design and allows only the trade-offs permitted by the rules. Both retain mandatory requirements; modeling cannot waive them. The prescriptive-versus-performance guide provides a path-selection checklist.

The first question is not whether performance is “better,” but whether it can evaluate the design decision at hand. If a larger glazed opening is important, an option study can test eligible combinations while keeping mandatory measures intact. If a straightforward prescriptive path already fits, elaborate modeling may add cost without improving the permit package. Confirm the actual project type, edition and software rules before selecting either approach.

Five stages: preliminary studies to the permit handoff

Preliminary studies compare decisions using explicitly provisional inputs. Final modeling records the selected, coordinated design. Keep those milestones separate so an early favorable run does not become a misleading promise about a later drawing set.

1. 1. Intake: establish the plans, scope and code basis

   The owner or designer supplies the current plans, accepted application date, building classification, conditioned-area boundaries, orientation and schedules. Confirm the project-location climate-zone basis using appropriate CEC tools and project records, not a county-wide guess. Identify existing, altered and new features separately. Use what to send, the detailed energy-consultant intake checklist and the code-cycle guide; current guidance is the 2025 Energy Code for applications on or after January 1, 2026, subject to the actual permit history.

2. 2. Baseline model: check the first coordinated run

   The preparer builds the initial proposed-design model from the supplied geometry, assemblies and equipment information. The software generates the applicable standard-design comparison. Here “baseline run” means the initial proposed option, not an energy audit or proof of concealed existing conditions. Check area, window orientation, system assignments and edition before interpreting the result. The designer confirms inputs; unknown specifications remain labeled assumptions rather than invented favorable values.

3. 3. Option studies: compare controlled design choices

   Agree which variables can change: for example, a window package, an assembly improvement or a coordinated equipment alternative. Hold the other inputs and model boundary constant for each controlled comparison. Record the changed measure, result, cost/constructability questions and required verification commitments. Compare a bundle only when the owner and designers understand the entire bundle. Preliminary runs guide a decision; they are not the final permit CF1R or NRCC package.

4. 4. Compliance package: replace assumptions with selected specifications

   The responsible designers confirm final schedules, assemblies and systems. The preparer updates the model, reruns the selected design and coordinates compliance output with the named drawing revision. Check that window U-factor/SHGC, HVAC efficiencies and required measures agree across the package. If the design changed, do not reuse an old result. Unresolved inputs are an action list, not a reason to label preliminary output permit-ready.

5. 5. CF1R or NRCC handoff and required registry coordination

   For applicable single-family work, hand off the CF1R and required measures with clear installer CF2R and ECC-Rater CF3R responsibilities. Where registration is required, the applicant and responsible signatories arrange the approved ECC-Provider process and registered permit copy; preparation does not claim registry operation or included registry fees. Nonresidential work uses applicable NRCC design documents and separate construction/acceptance responsibilities, not residential certificates. See CF1R/CF2R/CF3R coordination and the certificate responsibility guide.

Worked comparison: a 450 sq ft addition and two boundaries

Fictional educational example—not an actual software run, engineering determination or promise of compliance: add 450 sq ft to an existing 1,550 sq ft single-family house. The addition has 90 sq ft of glazing with illustrative U-factor 0.30 and SHGC 0.25, plus the same proposed heat-pump selection and duct layout in each study. Those window ratings are example inputs, not statewide required values. No parcel climate zone or local rule is assumed.

The owner also proposes a roof/ceiling efficiency upgrade in the existing house. For this illustration only, assume review confirms that improvement is eligible, properly evidenced and included in the permitted scope. Addition-alone does not claim that out-of-boundary improvement. Existing-plus-addition-plus-alterations includes the affected existing house and agreed upgrade under the applicable software rules. Where existing-condition verification is required to support a credit, arrange it before the relevant work conceals the evidence; photographs alone do not establish every permitted baseline.

For current metrics, the CEC 2025 Energy Code overview describes long-term system cost (LSC) and source energy, with additions/alterations required to meet LSC. Applicable new-construction checks include source energy and the relevant LSC budgets. Do not transplant an older TDV/EDR threshold into a current report. The table simplifies one LSC comparison into a unitless teaching index: each model’s own standard-design LSC is set to 100. These are made-up arithmetic values, not official report units, energy bills or complete compliance results.

What the architect learns—and what the numbers do not prove

The addition’s glazing and HVAC selections are unchanged in the first two rows. The outcome differs because the boundary, its standard design and eligible existing-building commitments differ—not because a larger house automatically creates free credit. The sensitivity row shows why removing the existing-roof improvement can undo the apparent benefit. Never compare 104 and 98 as absolute whole-building energy use: both are normalized to different standard designs. Only each row’s proposed-versus-standard relationship is meaningful here.

If the permit truly covers only an addition and the applicable rules allow it, addition-alone can avoid collecting unnecessary whole-house information. If the owner is genuinely altering existing features and can support the required inputs and commitments, a combined study may be worth evaluating. Neither boundary is universally easier or correct. Review the addition-alone versus existing-plus-addition guide and CEC additions/alterations chapter before choosing. The chapter distinguishes new, altered and existing features and the effect of existing-condition verification on baseline assumptions.

The practical decision is whether the proposed improvement belongs in the owner’s real scope, budget and drawings. A favorable option must carry its construction and verification obligations into the final package. Check every applicable budget and mandatory measure in the approved software; passing this illustrative LSC check alone is not a complete compliance determination. This example is educational, not legal or mechanical-design advice.

Order the study you need, not an undefined series of reruns

Agree the question, model boundary, number of option comparisons and intended final deliverable at intake. A window study, a permit package and a full rebuild of an inherited model are different scopes. Send previous reports and source-model availability for revisions; do not assume a PDF can recreate every original input. The plan-check corrections service explains error corrections, design revisions and major model rebuilds without treating them as interchangeable.

Use the existing simple residential/commercial square-footage pricing and additional-dwelling-unit rules; this page introduces no new rates. Confirm option-study scope, exclusions and completeness before production. To get a project-specific scope, start a quote request and upload plans, with a short list of the choices you want compared. The how-it-works overview explains the handoff. Intake records a request, not payment, a production acceptance or permit approval.

Title 24 Lab remains a provisional brand. Design-document preparation is not field testing, mechanical design or a claim to be an ECC-Provider. Current residential verification uses ECC terminology; older searches and older-cycle documents may say HERS, which should not be silently relabeled. Use the applicable CEC single-family manual and project edition when deciding the documentation path. The HERS-to-ECC applicant guide explains legacy comments and current verification responsibilities. Before choosing a model boundary, use the ADU classification guide or tenant-improvement scope checklist to identify affected space and systems.

Taking a new-building option study to permit

Comparing modeled options and documenting a selected building are different milestones. If this study is for a new dwelling or nonresidential building, use the new-construction workflow to identify who confirms final schedules, coordinates the compliance output with drawings and arranges construction-stage documentation. Keep provisional assumptions labeled until the responsible designers resolve them; a preliminary result does not certify later substitutions or installed work. For applicable residential work, use the CF1R preparation and CF2R/CF3R handoff workflow to assign design, installer and ECC-Rater responsibilities.

Typical scope

• +A scoped model tied to supplied plans, the applicable software/edition and agreed building boundary.
• +Agreed option runs comparing eligible design choices, with provisional inputs identified.
• +Coordination of selected modeled measures with the designer’s current schedules and drawings.
• +Applicable design compliance output and an installation/verification responsibility handoff.

Documentation deliverables

Typical report-preparation outputs to confirm in the project scope; not a promise of field services or permit approval.

• +An input/assumptions record identifying the plan revision, scope, edition and unresolved selections.
• +An option comparison recording changed inputs, applicable budget results and required construction commitments—not utility-bill forecasts.
• +Final applicable CF1R or NRCC design output for the selected package, with required signatures/registration responsibilities identified.
• +A handoff of modeled measures, outstanding coordination items and applicable verification commitments. File/model delivery and comparison scope are agreed at intake.

Not included / not implied

• -Permit approval is decided by the building department; documentation does not guarantee approval.
• -Construction-stage installation certificates and ECC verification are separate responsibilities; field testing and installer certification are not included in report preparation.
• -CALGreen (Title 24, Part 11) documentation, permit processing and acceptance testing are separate scopes, not implied by a Part 6 energy report.
• -Structural, mechanical design or legal advice.
• -ECC field testing, acceptance testing, registry fees, CALGreen documentation and AHJ permit fees are excluded from the published preparation prices. Registry operation, installation certification and field verification remain separate responsibilities.

Questions