Why Do I Need Title 24 Calculations?

Call (626) 365-1518 | Alternative Energy Systems

Why Do I Need Title 24 Calculations is a practical question when architectural plans already show the building, windows, walls, roof, rooms, and equipment locations.

The reason is that construction drawings describe what you intend to build, while Title 24 calculations evaluate how the energy-related parts of that design work together under California’s Building Energy Efficiency Standards.

Depending on the project, the calculations can evaluate:

• Building size
• Conditioned floor area
• Building orientation
• California climate zone
• Exterior wall assemblies
• Roof and ceiling assemblies
• Floor assemblies
• Insulation
• Window area
• Window performance
• Glazed exterior doors
• HVAC equipment
• Duct systems
• Ventilation
• Water heating
• Commercial lighting and controls when applicable
• Other regulated building systems

The calculations help determine whether the proposed energy design satisfies the applicable compliance path or whether changes should be considered before the permit documents are finalized.

They also create a technical basis for the compliance forms submitted with the construction plans.

Alternative Energy Systems brings more than 30 years of California energy-compliance experience to residential, multifamily, mixed-use, and commercial projects.

Call (626) 365-1518 if you need calculations prepared for a current project or need existing energy documentation reviewed.

Title 24 Calculations Turn Building Plans Into Measurable Energy Compliance

A set of architectural plans can show that a wall contains insulation or that a building has energy-efficient windows.

That does not necessarily establish whether the complete proposed design satisfies the applicable California Energy Code requirements.

The calculations place measurable values behind those design decisions.

For example, they can consider:

• How much glazing the building has
• Where that glazing is located
• How efficiently the glazing performs
• How much insulation is included in different assemblies
• What HVAC system serves the building
• Where ducts are located
• How water is heated
• How the complete design performs in the applicable climate zone

That information provides a more complete picture than looking at any one component by itself.

Why Can’t the Building Department Just Look at the Plans?

Some energy characteristics cannot be determined from architectural drawings alone.

Two windows that look identical on an elevation may have different:

• U-factors
• Solar heat gain coefficients

Two HVAC units that occupy the same space can have different efficiencies.

Two wall assemblies can look similar on a floor plan while using different insulation values or construction methods.

The calculations organize these technical characteristics so the applicable energy requirements can be evaluated consistently.

What Do Title 24 Calculations Actually Prove?

The calculations are used to demonstrate how a particular project addresses the applicable Energy Code.

Depending on the compliance method, that can mean showing that:

• Applicable mandatory requirements are addressed
• Prescriptive requirements are satisfied
• The proposed design meets the applicable performance requirements

For performance compliance, approved software evaluates the proposed building against the applicable standard design.

The purpose is not simply to generate a pass/fail label.

The calculation identifies the energy-related characteristics that make up the compliant design.

Performance Calculations Allow Building Features to Work Together

One of the major benefits of performance compliance is the ability to evaluate the building as a system.

A project does not necessarily succeed or fail because of one component alone.

For example, a building with a large amount of glazing may potentially improve performance elsewhere through measures involving:

• Better window specifications
• Improved insulation
• More efficient HVAC equipment
• Roof improvements
• Other qualifying energy measures

The calculation evaluates the interaction among those features.

This can provide more design flexibility than treating every building component independently.

Prescriptive Compliance Is Different From Performance Calculations

Not every project requires a full performance model.

California also allows applicable projects to demonstrate compliance through prescriptive requirements.

Under a prescriptive approach, the project follows specific requirements established for applicable components and systems.

Depending on the scope, that can involve:

• Insulation levels
• Window performance
• Roof requirements
• HVAC efficiency
• Water heating
• Lighting requirements
• Other applicable measures

The appropriate compliance method depends on the project.

A smaller alteration may need limited prescriptive documentation, while a new home or more complex project may benefit from performance analysis.

Not Every Project Needs the Same Type of Calculation

The amount and type of analysis depend on:

• Building classification
• Project scope
• Climate zone
• Whether the work is new construction
• Whether the work is an addition
• Whether the work is an alteration
• Systems being modified
• Selected compliance method

That is why one energy report should not simply be copied from another project.

Climate Zone Is an Important Part of the Calculation

California uses 16 building climate zones.

Performance budgets and certain prescriptive requirements vary according to climate zone and building type.

This matters because buildings in different parts of California experience different:

• Heating loads
• Cooling loads
• Outdoor temperatures
• Solar conditions
• Seasonal energy demands

The calculation therefore needs the correct project location and climate-zone information.

Why Building Orientation Matters

Orientation affects how the building interacts with the sun.

Windows facing different directions can receive different amounts of solar exposure.

For projects using performance analysis, the relationship among:

• North-facing glazing
• South-facing glazing
• East-facing glazing
• West-facing glazing

can influence the modeled building performance.

This is one reason the calculation needs an actual project plan instead of only a total square-foot number.

Window Area Can Have a Significant Effect on the Calculation

Windows are an important part of the building envelope.

The analysis may consider:

• Total window area
• Window size
• Window orientation
• U-factor
• Solar heat gain coefficient
• Glazed exterior doors

A building with extensive glazing may perform differently from another building of similar size with much less glass.

That difference needs to be reflected in the energy analysis.

Why Window U-Factor Is Included

U-factor describes thermal performance associated with a window or glazed assembly.

Lower heat transfer through glazing can influence overall building performance.

The value used in the energy calculation should correspond to the product eventually selected for the project.

If the contractor later substitutes a window with different performance values, the energy documentation may need review.

Why Solar Heat Gain Coefficient Is Included

Solar heat gain coefficient relates to the amount of solar energy passing through glazing.

That can affect cooling performance, particularly where solar exposure is significant.

The effect also interacts with:

• Window orientation
• Window area
• Climate zone
• Overall building design

This is another reason the calculations evaluate the complete project rather than simply verifying that windows are labeled energy efficient.

Insulation Is Evaluated as Part of the Complete Envelope

Title 24 calculations can incorporate insulation associated with:

• Exterior walls
• Roofs
• Ceilings
• Attics
• Floors
• Other thermal boundaries

Different assemblies can have different energy characteristics.

The architectural sections and energy calculations should therefore describe compatible construction.

Roof Construction Can Affect Energy Performance

The roof is exposed to outdoor temperatures and solar conditions.

Depending on the project, calculations can consider:

• Roof insulation
• Ceiling insulation
• Attic configuration
• Roofing characteristics
• Applicable cool-roof measures

A roof design should not be changed after the report is completed without checking whether that change affects the energy documentation.

HVAC Efficiency Is Part of the Energy Analysis

Heating and cooling equipment can be a major part of building energy use.

Calculations may include information involving:

• System type
• Heating efficiency
• Cooling efficiency
• Heat-pump systems
• Number of systems
• Controls
• Duct configuration

If the mechanical design changes after the original calculation, the report may require review.

Duct Location Can Change the Result

Duct systems located inside conditioned space can interact with the building differently from ducts located in:

• Attics
• Crawlspaces
• Garages
• Other unconditioned areas

The energy analysis should reflect the actual proposed duct configuration rather than an assumption that is later changed during construction.

Ventilation Must Be Coordinated With the Mechanical Design

Energy-efficient buildings also need appropriate ventilation.

Depending on the building type and scope, the analysis and compliance documentation can involve:

• Whole-building ventilation
• Local exhaust
• Outdoor-air systems
• Other applicable ventilation measures

The energy report should remain coordinated with the mechanical plans.

Water Heating Can Affect the Calculations

Water heating is another important building energy use.

The analysis may include:

• Equipment type
• Energy source
• Efficiency
• Heat-pump water heating
• Central systems
• Individual systems
• Other applicable characteristics

Changing the water-heating system after the calculations are completed can affect the compliance package.

Commercial Projects Can Require Lighting Calculations

For nonresidential projects, Title 24 calculations can also address commercial lighting.

Depending on the project, this may involve:

• Fixture types
• Fixture quantities
• Fixture wattage
• Space use
• Lighting power
• Lighting controls
• Daylighting controls
• Exterior lighting

Commercial lighting documentation should match the electrical and architectural drawings.

Title 24 Calculations Help Identify Problems Before Plan Check

The calculations are valuable before permit submission because they can reveal incomplete or conflicting project information.

AES may identify questions such as:

• Does the conditioned floor area match throughout the plans?
• Are all windows shown in the schedule?
• Have window-performance values been identified?
• Do the wall sections identify insulation?
• Is the roof assembly complete?
• Has the HVAC equipment been selected?
• Are duct locations shown?
• Is the water-heating system clear?
• Are commercial lighting schedules complete?

Resolving those issues before formal plan review can reduce preventable corrections.

The Calculations Help Coordinate the Report With the Plans

One of the most common sources of permit problems is a disagreement between the energy documentation and the construction drawings.

Examples include:

• The report shows one floor area while the plans show another
• The report uses one window specification while the schedule lists another
• The report assumes one insulation assembly while the section shows another
• The report uses one HVAC system while the mechanical plan shows another

A correct calculation based on outdated plans can still create problems.

The report and drawings need to describe the same current design.

The Calculations Can Identify Which Specifications Need to Be on the Plans

Once the compliant design is established, the project team can identify which energy-related specifications need to remain part of the final construction documents.

These may include:

• Window-performance requirements
• Insulation values
• Roof characteristics
• Mechanical efficiencies
• Duct requirements
• Water-heating specifications
• Commercial lighting measures

This gives the architect and contractor clearer information about what must be preserved during construction.

The Calculations Can Help With Product Selection

Calculations can influence decisions before products are purchased.

For example, the project team can compare proposed:

• Windows
• HVAC systems
• Water heaters
• Insulation assemblies
• Other energy-related products

against the assumptions in the energy documentation.

That can help reduce the risk of purchasing something that conflicts with the approved design.

They Can Also Reveal Design Tradeoffs

Performance analysis can be useful when the design team wants to preserve an architectural feature that does not follow a simple prescriptive approach.

For example, the project might prioritize:

• More glazing
• A particular window configuration
• A certain roof design
• A preferred mechanical system

The energy model can help determine whether qualifying improvements elsewhere in the design can support the proposed configuration.

The final solution still needs to comply with mandatory requirements and the applicable performance rules.

Why Do I Need Title 24 Calculations for a New Home?

New residential construction needs to address the applicable California Energy Code requirements.

A whole-building analysis can evaluate how the home’s:

• Geometry
• Orientation
• Envelope
• Glazing
• Insulation
• HVAC
• Duct systems
• Ventilation
• Water heating

work together.

The calculations then provide the technical basis for the applicable compliance forms.

Why Do I Need Title 24 Calculations for an ADU?

ADUs can require energy-compliance analysis whether they are:

• New detached structures
• Attached additions
• Garage conversions
• Conversions of other existing spaces

A detached ADU may need to be evaluated as a complete new residential structure.

A conversion may require the analysis to distinguish existing construction from the new conditioned space.

For additional information, review ADU Title 24.

Why Do I Need Title 24 Calculations for an Addition?

An addition introduces new conditioned space and new envelope components.

The project may add:

• Exterior walls
• Roof area
• Windows
• Insulation
• Heating and cooling loads

Depending on the project, compliance may be demonstrated through a prescriptive or performance method.

The calculations or applicable forms establish which requirements apply to the proposed addition.

Why Do I Need Title 24 Calculations for a Garage Conversion?

A garage conversion can change unconditioned space into conditioned living space.

The project may need to address:

• Existing wall construction
• New wall insulation
• Ceiling or roof insulation
• Floor conditions
• Windows
• HVAC
• Ventilation

The analysis helps define what the converted space needs to include as part of the current design.

Why Do I Need Title 24 Calculations for a Remodel?

Not every remodel requires the same analysis.

However, energy compliance can become relevant when the project changes:

• Windows
• Exterior walls
• Insulation
• Roofing
• HVAC systems
• Ducts
• Water heating
• Commercial lighting

A limited alteration may use prescriptive or system-specific documentation instead of a full whole-building performance calculation.

Why Do I Need Title 24 Calculations for a Multifamily Project?

Multifamily buildings have their own applicable Energy Code requirements and compliance documentation.

The analysis can involve:

• Dwelling units
• Common areas
• Envelope systems
• Central mechanical systems
• Individual mechanical systems
• Water heating
• Lighting
• Other applicable features

The project should be classified correctly before the calculations are prepared.

Why Do I Need Title 24 Calculations for a Commercial Project?

Commercial projects can involve several interacting energy systems.

Depending on the project, the analysis may evaluate:

• Building envelope
• Storefront glazing
• Mechanical systems
• Ventilation
• Service water heating
• Interior lighting
• Exterior lighting
• Lighting controls

Commercial projects can also involve coordination among architects, mechanical engineers, electrical designers, lighting designers, contractors, and property owners.

For related professional services, review Title 24 compliance services and Title 24 energy analysis.

Do Title 24 Calculations Guarantee Permit Approval?

No.

The calculations support the energy-compliance portion of a permit package.

A building department may also review:

• Architectural requirements
• Structural requirements
• Electrical requirements
• Mechanical requirements
• Plumbing requirements
• CALGreen requirements
• Fire and life-safety requirements
• Other applicable codes

A properly prepared energy analysis does not guarantee approval of the entire construction project.

Can the Building Department Require Revised Calculations?

Yes.

Revisions may be necessary when:

• The plans change
• The conditioned floor area changes
• Windows change
• Insulation changes
• The roof design changes
• HVAC equipment changes
• Water heating changes
• Commercial lighting changes
• The building department identifies incomplete or inconsistent information

The revised calculations should reflect the actual current project rather than simply modifying isolated numbers.

Do Calculations Need to Be Updated if the Contractor Changes Equipment?

Potentially.

If a product substitution changes an input used in the approved analysis, the existing documentation should be reviewed.

This can include changes to:

• Windows
• HVAC systems
• Water heaters
• Insulation assemblies
• Other modeled or specified components

A substitution that appears equivalent by size or function is not necessarily equivalent for energy compliance.

Can I Reuse Title 24 Calculations From Another Project?

No project-specific energy calculation should automatically be reused for a different building.

The analysis can depend on:

• Address
• Climate zone
• Building type
• Floor area
• Geometry
• Orientation
• Windows
• Envelope construction
• Mechanical systems
• Water heating

Two similar-looking buildings can therefore produce different energy results.

Can I Reuse Old Calculations From the Same Building?

Old calculations can sometimes provide useful background, but they should not automatically be submitted for new work.

The previous analysis may reflect:

• An older Energy Code cycle
• An earlier project scope
• Old windows
• Old HVAC equipment
• Different floor area
• Different construction plans

AES can review the old report together with the current plans.

The Current Energy Code Requires Current Compliance Methods

For applicable permit applications filed on or after January 1, 2026, California uses the 2025 Building Energy Efficiency Standards.

When the performance compliance method is used, approved 2025 compliance software is required.

CEC-approved software evaluates the proposed project using the modeling rules established for the current Energy Code.

For official information about current compliance software, review the California Energy Commission 2025 Energy Code Compliance Software page.

What Information Is Needed Before Calculations Can Be Completed?

Helpful project documents can include:

• Floor plans
• Exterior elevations
• Building sections
• Roof plans
• Window schedules
• Window specifications
• Insulation information
• HVAC specifications
• Duct-location information
• Ventilation information
• Water-heating information
• Commercial lighting plans when applicable
• Commercial lighting-control information when applicable
• Existing energy reports
• Building-department correction comments

Not every project requires every item.

AES can review what is available and identify missing information.

Before submitting documents, review what AES will need from you.

How Are Title 24 Calculations Prepared?

The process begins with the actual project rather than a generic template.

1. Identify the Project Scope

AES determines whether the project involves new construction, an ADU, addition, conversion, alteration, multifamily project, commercial tenant improvement, HVAC work, lighting work, or another applicable scope.

2. Review the Plans

The building geometry, envelope, windows, mechanical systems, and other applicable information are reviewed.

3. Confirm the Climate Zone and Building Classification

The correct project location and building type are important inputs.

4. Identify Missing Information

Incomplete specifications or conflicting plan information are identified before final analysis.

5. Complete the Applicable Compliance Analysis

The project is evaluated through the applicable prescriptive or performance compliance method.

6. Prepare the Compliance Documentation

The resulting forms identify the energy measures associated with the proposed design.

7. Coordinate the Results With the Plans

The final energy requirements should agree with the current construction drawings.

Why Early Calculations Can Make the Design Process Easier

Starting before the plans are completely finalized gives the project team time to address energy issues while design decisions are still flexible.

Early review can identify:

• Glazing that affects performance
• Missing insulation requirements
• Mechanical-system questions
• Roof-performance issues
• Incomplete lighting information
• Other energy-related conflicts

Waiting until immediately before permit submission can turn ordinary design decisions into last-minute plan revisions.

Why Choose Alternative Energy Systems?

Alternative Energy Systems provides professional Title 24 calculations, compliance reports, revisions, and energy-related plan-check support throughout California.

AES brings more than 30 years of California energy-compliance experience to:

• New residential construction
• ADUs
• Garage conversions
• Additions
• Residential remodels
• Multifamily projects
• Mixed-use buildings
• Commercial construction
• Office tenant improvements
• Retail projects
• Restaurant projects
• Warehouse alterations
• HVAC projects
• Commercial lighting projects
• Energy-related plan-check corrections

AES prepares calculations using the actual building plans and available specifications so the resulting documentation corresponds to the project being permitted.

Learn more through the About Us page or review company background on the clients page.

Get Title 24 Calculations Based on Your Actual Project

Call (626) 365-1518 | Alternative Energy Systems

Understanding Why Do I Need Title 24 Calculations comes down to one central point:

California energy requirements must be applied to the actual building being designed.

The calculations provide a way to evaluate how the proposed:

• Building geometry
• Climate zone
• Envelope
• Windows
• Insulation
• Roof
• HVAC systems
• Ducts
• Ventilation
• Water heating
• Commercial lighting when applicable

work together under the applicable compliance method.

They also create the technical basis for energy-compliance documentation that can be coordinated with the permit drawings.

Alternative Energy Systems can review your plans, identify the information needed, prepare the applicable calculations, and assist with energy-related revisions or plan-check comments.

Call (626) 365-1518 or begin through the contact page.

When service and payment have already been arranged, payment can be completed through the AES payment page.

Frequently Asked Questions: Why Do I Need Title 24 Calculations?

Why Do I Need Title 24 Calculations?

They evaluate the energy-related characteristics of a California building project and provide the technical basis for demonstrating compliance with the applicable Energy Code requirements.

Are Title 24 calculations the same as architectural plans?

No. Architectural plans describe the proposed construction, while energy calculations evaluate energy-related features within that design.

What do the calculations evaluate?

Depending on the project, they can evaluate building geometry, climate zone, orientation, windows, insulation, roofs, HVAC, ducts, ventilation, water heating, lighting, and other applicable systems.

Why does conditioned floor area matter?

Conditioned floor area helps define the building space being heated or cooled and is an important project characteristic in energy analysis.

Why does climate zone matter?

California uses 16 building climate zones, and performance budgets and certain prescriptive requirements vary according to climate zone and building type.

Why does building orientation matter?

Orientation can affect solar exposure through windows and therefore influence building heating and cooling performance.

Why are windows included?

Window area, orientation, U-factor, solar heat gain coefficient, and other fenestration characteristics can significantly affect building energy performance.

Why is insulation included?

Insulation affects heat transfer through walls, roofs, ceilings, floors, and other parts of the thermal envelope.

Why is HVAC included?

Heating and cooling systems are major energy users, and equipment type, efficiency, ducts, and controls can affect compliance.

Why are ducts included?

Duct location, sealing, insulation, airflow, and other conditions can affect mechanical-system energy performance.

Why is ventilation included?

Applicable ventilation systems need to be coordinated with mechanical design and Energy Code requirements.

Why is water heating included?

Water heating is a significant building energy use and can affect the applicable compliance analysis.

Why is commercial lighting included?

Nonresidential Energy Code compliance can regulate lighting power, fixture wattage, controls, daylighting, and other lighting measures.

Do all projects need performance calculations?

No. Some projects can comply through applicable prescriptive requirements or system-specific forms rather than whole-building performance modeling.

What is performance compliance?

Performance compliance uses approved energy-modeling software to compare a proposed building against the applicable standard design or energy budget.

What is prescriptive compliance?

Prescriptive compliance follows specific component and system requirements established by the Energy Code.

Can calculations provide design flexibility?

Performance analysis can allow qualifying energy-efficiency tradeoffs among different building features while still satisfying applicable mandatory and performance requirements.

Do new homes need Title 24 calculations?

New homes are subject to applicable Energy Code requirements. The exact calculations and forms depend on the compliance method.

Do ADUs need Title 24 calculations?

Applicable ADUs require energy-compliance documentation based on whether they are detached, attached, or conversions and on the selected compliance method.

Do additions require calculations?

Applicable additions require Energy Code compliance, which may be demonstrated through a prescriptive or performance method depending on the project.

Do garage conversions require calculations?

They commonly require energy-compliance review because unconditioned space is being converted into conditioned living space.

Do remodels require calculations?

Some do. Alterations affecting regulated energy components can require prescriptive, performance, or system-specific compliance documentation.

Do commercial tenant improvements need calculations?

They can. Lighting, mechanical systems, ventilation, water heating, glazing, and other altered systems can trigger nonresidential Energy Code requirements.

Can Title 24 calculations reduce plan-check problems?

Accurate, coordinated calculations can help identify missing or conflicting energy information before submittal, although they cannot guarantee that the building department will issue no corrections.

Do Title 24 calculations guarantee permit approval?

No. Energy compliance is only one portion of the complete building permit review.

Can calculations be revised?

Yes. Revisions may be necessary when energy-related features of the design change.

Do calculations need to match the plans?

Yes. The energy analysis and construction drawings should represent the same current project.

Can I reuse calculations from another project?

No project-specific analysis should automatically be reused. Address, climate zone, floor area, orientation, windows, envelope, and building systems can all differ.

Can I reuse old calculations from the same property?

They may provide background, but the applicable code cycle, construction scope, plans, and building systems should be reviewed before reuse.

What Energy Code is currently used?

For applicable permit applications filed on or after January 1, 2026, California uses the 2025 Building Energy Efficiency Standards.

What software is used for performance compliance?

Performance calculations under the current code must use software approved by the California Energy Commission for the applicable building type and project scope.

What should I send AES to begin?

Current floor plans, elevations, sections, roof plans, window information, insulation details, HVAC specifications, water-heating information, commercial lighting information when applicable, and any existing correction comments are useful starting documents.

How do I get started?

Call Alternative Energy Systems at (626) 365-1518 and provide the current project plans for review.