Title 24 for an ADU: Energy Forms and Plan-Check Requirements

Every accessory dwelling unit built or permitted in California must satisfy title 24 adu energy standards before the local building department will issue a building permit. Title 24, Part 6 of the California Code of Regulations establishes mandatory building energy efficiency standards governing wall insulation, window heat transmission, heating and cooling equipment, water heaters, and ventilation.

In This Guide

1. Which Code Edition Governs Your Permit Application?
2. Title 24 Rules by ADU Type: Detached, Conversion, or Addition
3. The Document Chain: CF1R, CF2R, and CF3R Forms
4. Prescriptive vs. Performance Compliance Paths
5. Core Energy Components: Insulation, Glazing, and Heat Pumps
6. Homeowner Coordination Checklist for Title 24
7. Frequently Asked Questions

Which Code Edition Governs Your Permit Application?

California updates its Building Standards Code every three years through the California Energy Commission (CEC). When planning title 24 compliance for adu california projects, your requirements depend on the exact date your application is formally accepted for plan check by your municipal building department:

• The 2022 California Energy Code: Governs all complete permit applications officially submitted to the city between January 1, 2023, and December 31, 2025. It established high-efficiency heat pumps as the prescriptive baseline for space and water heating in new construction.
• The 2025 California Energy Code: Takes effect for all permit applications submitted on or after January 1, 2026. The 2025 edition refines residential ventilation standards, increases electric readiness mandates, and optimizes heat pump performance baselines across California's 16 distinct climate zones.

The date of permit submittal, not the date construction begins or when plans are approved, locks in your governing code standards. If your plans are formally accepted by the city on December 28, 2025, your project remains governed by the 2022 Energy Code even if plan check review extends into mid-2026.

Title 24 Rules by ADU Type: Detached, Conversion, or Addition

Title 24 treats different ADU construction types under distinct regulatory umbrellas. How your unit is classified dictates whether you must satisfy full new-construction standards or relaxed alteration rules:

ADU Classification	Title 24 Regulatory Status	Envelope & Insulation Requirements	Solar PV Mandate	HERS Verification Required
Newly Built Detached ADU	Newly Constructed Low-Rise Residential Building	Full Title 24 envelope: 2x6 walls, continuous exterior insulation, U-0.30 windows	Yes (mandatory unless meeting small size or roof shade exceptions)	Yes (duct leakage, ventilation, refrigerant charge)
Attached ADU Addition	Residential Addition	Applies only to the new exterior envelope and newly added mechanical equipment	No (additions to existing homes are exempt from solar PV)	Yes (for newly added HVAC ducts or equipment)
Garage Conversion to ADU	Unconditioned Space to Conditioned Living Space Addition	Must insulate existing 2x4 stud walls, seal concrete slab, insulate roof to R-30	No (conversion of existing building volume is exempt from solar)	Yes (duct testing if ducted system; exempt if ductless mini-split)
Junior ADU (JADU)	Internal Alteration of Existing Conditioned Space	Existing envelope is already conditioned; applies only to new lighting and fixtures	No	Rarely (only if dedicated new ducted HVAC is installed)

1. Newly Constructed Detached ADUs

A standalone backyard cottage is classified as a brand-new residential dwelling. It must comply with all whole-building energy provisions. This includes high-performance walls (typically 2x6 studs with R-20 cavity insulation plus R-4 continuous exterior rigid foam), minimum R-30 to R-38 roof insulation, maximum 0.30 window U-factors, and whole-house mechanical ventilation under ASHRAE 62.2 rules. Solar photovoltaic panels are mandatory under Section 150.1(c)14 unless the building qualifies for a shade or minimal roof area exemption.

2. Attached ADUs (Additions)

An attached ADU built as an addition to an existing house must comply with energy rules for the new conditioned footprint. The energy calculations evaluate the newly added walls, roof, and windows, along with any newly installed mechanical equipment. Attached additions are legally exempt from the state solar panel mandate.

3. Garage Conversions to ADUs

Converting an existing detached or attached garage changes an unconditioned storage volume into conditioned living space. Under Title 24, this is processed under addition and alteration standards. You do not need to tear down existing 2x4 exterior framing, but you must add cavity insulation (minimum R-13 to R-15), seal the concrete slab against moisture, install high-efficiency heating and cooling, and insulate the roof. Garage conversions are exempt from solar PV installation. Explore our detailed guide on garage conversion to ADU for step-by-step structural details.

4. Junior ADUs (JADUs)

Because a Junior ADU (up to 500 square feet) is created entirely within the existing conditioned envelope of the primary single-family home, its exterior shell already complies with previous residential standards. Title 24 compliance is minimal, requiring only high-efficacy JA8-certified LED lighting, CalGreen-compliant low-flow plumbing fixtures, and proper mechanical ventilation if a dedicated bathroom is added.

For an overview of the broader permitting milestones that run parallel to energy calculations, consult our complete guide to the ADU building permit process.

The Document Chain: CF1R, CF2R, and CF3R Forms

Energy compliance is not a single form submitted once and forgotten. The California Energy Commission enforces a three-stage document chain that tracks energy specifications from the drawing board through final construction:

Design Stage (CF1R)  ──>  Construction Stage (CF2R)  ──>  Final Inspection (CF3R)
Architect & Consultant    Installing Contractors          Certified HERS Rater

Stage 1: The Certificate of Compliance (CF1R)

The CF1R form is the document required for municipal plan check submittal. It is generated by a certified energy consultant using state-approved compliance software (such as CBECC-Res or EnergyPro).

• Newly Constructed Buildings: Uses the CF1R-NCB-01-E performance compliance document.
• Additions and Conversions: Uses the CF1R-ADD-01-E or prescriptive envelope forms (CF1R-ENV-01-E).
• Registration Mandate: In most California jurisdictions, the CF1R must be registered with an approved HERS provider (CalCERTS or CHEERS) and carry an official digital registry watermark before the city will accept it.
• Drawing Set Requirement: City plan examiners require the complete multi-page CF1R report to be printed directly onto a full-size architectural drawing sheet (often Sheet T24-1) and signed by both the Documentation Author and the designer of record.

Stage 2: The Certificate of Installation (CF2R)

During construction, the licensed general contractor and trade subcontractors complete CF2R forms. These documents certify that the physical materials and equipment installed on site match the exact specifications listed on the approved CF1R.

For example, your insulation installer completes the CF2R-ENV-01-E verifying wall and ceiling R-values, while your mechanical contractor completes the CF2R-MCH-01-E confirming the make, model, SEER2 cooling rating, and HSPF2 heating efficiency of the installed heat pump.

Stage 3: The Certificate of Verification (CF3R)

Before your city building inspector conducts the final inspection and signs off on the Certificate of Occupancy, an independent third-party HERS Rater must visit the job site to conduct diagnostic testing and complete CF3R forms.

The HERS rater verifies:

• Duct Leakage Testing: Confirms ducted HVAC systems have less than 5 percent total air leakage. (Ductless mini-splits with less than 25 feet of ductwork are exempt from duct leakage testing).
• Blower Door Envelope Testing: Measures building envelope air tightness when required by performance calculations.
• Fan Efficacy and Airflow: Verifies continuous mechanical ventilation fans deliver required cubic feet per minute (CFM) under ASHRAE 62.2.
• Refrigerant Charge Verification: Confirms proper refrigerant levels on central split heat pump systems.

The HERS rater registers the passed CF3R forms directly into the CalCERTS or CHEERS database, where your municipal building inspector verifies them electronically before final approval.

Prescriptive vs. Performance Compliance Paths

When preparing your CF1R energy documentation, your design team selects one of two compliance paths recognized by Title 24:

The Prescriptive Path

The prescriptive method is a rigid checklist. Each individual building component must satisfy exact state-mandated efficiency numbers without exception:

• Hard maximum window and door area capped at 20 percent of total gross floor area.
• Mandatory wall insulation consisting of 2x6 framing with R-20 cavity insulation plus R-4 continuous exterior rigid foam in most climate zones.
• Mandatory dedicated heat pump water heater meeting strict efficiency tiers.

While conceptually straightforward, the prescriptive method is rarely used for modern ADUs because it offers zero design flexibility. If you want large floor-to-ceiling sliding glass doors to open your ADU to the backyard, the prescriptive path will fail your plans because your window-to-floor ratio exceeds 20 percent.

The Performance Path (Recommended)

Over 90 percent of permitted California ADUs use the performance path. Using CEC-approved computer modeling software, an energy consultant creates a digital 3D model of your ADU and simulates its energy use over an entire year across your local climate zone.

The software establishes an energy budget (measured in Time Dependent Valuation or TDV energy) based on a theoretical reference home. As long as your proposed ADU consumes equal to or less energy than the state budget, your design passes.

The performance path allows smart design trade-offs:

• Upgrade Mechanicals to Expand Glass: Installing a higher-efficiency ductless mini-split (such as 20+ SEER2) or upgrading ceiling insulation allows you to incorporate large 8-foot patio sliders that exceed prescriptive window caps.
• Avoid Thick Exterior Rigid Foam: Careful trade-offs often allow builders to use standard 2x4 framing with high-density spray foam or 2x6 walls without cumbersome exterior continuous foam boards, simplifying stucco and siding installation.

Core Energy Components: Insulation, Glazing, and Heat Pumps

To ensure your ADU passes Title 24 plan check on the first submittal, coordinate these three primary building systems early during architectural drafting:

1. High-Performance Windows and Doors

Fenestration (windows, sliding glass doors, and glazed entry doors) must carry certification labels from the National Fenestration Rating Council (NFRC):

• U-Factor: Measures heat loss. Most California climate zones mandate a maximum U-factor of 0.30 or lower.
• Solar Heat Gain Coefficient (SHGC): Measures solar heat radiation entering the home. Cooling-dominated climate zones mandate an SHGC of 0.23 or lower.

Temporary NFRC stickers must remain on all window glass until your city building inspector completes the final inspection. Removing these stickers prematurely is a common mistake that delays permit sign-off.

2. Space Heating and Cooling (HVAC)

Under current California standards, electric heat pumps serve as the baseline for residential space conditioning:

• Ductless Mini-Split Heat Pumps: The most popular choice for California ADUs. They eliminate ductwork entirely, avoiding costly HERS duct blast testing, and provide independent temperature zones for living rooms and bedrooms.
• Gas Furnaces: Installing natural gas heating in a new detached ADU carries severe performance penalties under Title 24, requiring expensive compensating upgrades elsewhere in the building envelope.

3. Domestic Water Heating

Water heating represents roughly 25 to 30 percent of an ADU's annual energy budget:

• Heat Pump Water Heaters (HPWH): The standard prescriptive baseline. Compact 50-gallon hybrid heat pump water heaters (from manufacturers like Rheem or Bradford White) fit cleanly into an exterior mechanical closet.
• Tankless Electric vs. Tankless Gas: Electric resistance tankless water heaters consume immense peak wattage and struggle to pass Title 24 performance modeling without massive solar arrays. Tankless natural gas water heaters can pass in additions and conversions where gas lines already exist, but heat pumps remain the cleanest compliance path for new detached builds.

Homeowner Coordination Checklist for Title 24

Use this coordination checklist with your designer and energy consultant before submitting plans to your municipal building department:

• Identify California Climate Zone: Confirm which of California's 16 climate zones applies to your parcel (for example, Los Angeles coastal is Zone 6, while inland valleys are Zones 9 or 14).
• Finalize Window and Door Schedules: Confirm window sizes, glass types, and verified NFRC ratings (U-factor ≤ 0.30 and SHGC ≤ 0.23).
• Specify Exact HVAC Equipment: Record the exact manufacturer, model number, SEER2 cooling rating, and HSPF2 heating rating for your heat pump.
• Specify Water Heater Type: Verify your water heater make, storage volume, and Uniform Energy Factor (UEF) rating.
• Verify Solar PV Strategy: For detached new builds, confirm roof layout for solar panels or document shaded roof exemptions with certified aerial canopy measurements.
• Register the CF1R: Ensure your energy consultant registers your calculation report with CalCERTS or CHEERS and generates an official registry watermark.
• Print CF1R Directly on Permit Sheets: Confirm that the complete Title 24 energy report is embedded onto full-size drawing sheets in your architectural plan set.
• Hire a Certified HERS Rater Early: Contact a local certified HERS rater before closing up walls to schedule mandatory rough framing and final duct/blower door testing.

Frequently Asked Questions

Does every ADU in California require Title 24 calculations?

Yes. Every permitted ADU in California requires Title 24 energy documentation. Newly constructed detached units and additions converting unconditioned garages must submit a certified CF1R energy report to obtain building permits. Even small internal Junior ADUs must comply with mandatory lighting, plumbing, and mechanical efficiency rules, though their paperwork is significantly simpler.

How much does a Title 24 report cost for an ADU?

A professional residential Title 24 energy calculation report for an ADU typically costs between $250 and $550 when prepared by an independent energy consultant. When you work with a full-service design firm like Build With A Plan, Title 24 energy modeling and plan sheet integration are bundled directly into the permit design package. Third-party HERS rater field inspections during construction typically cost between $400 and $800.

Are solar panels required on all California ADUs under Title 24?

No. Solar photovoltaic (PV) panels are only required on newly constructed, standalone detached ADUs. If you build an attached ADU addition, convert an existing garage, or finish a basement, solar panels are not required by state law. Furthermore, detached ADUs qualify for solar exemptions if the roof is shaded by mature trees or adjacent buildings, or if the roof surface area is too small to host a minimal 1.8 kW DC array.

Can I do my own Title 24 calculations?

Practically speaking, no. While California law technically allows property owners to prepare prescriptive forms, municipal building departments almost universally reject hand calculations for accessory dwellings. Title 24 plan check requires computer simulation files generated by CEC-certified software (like CBECC-Res) registered in an approved state HERS database. Working with an experienced energy consultant ensures your plans pass plan check without correction notices.

What happens if my ADU fails HERS testing after construction?

If a HERS rater identifies excessive duct leakage (over 5 percent) or improper mechanical ventilation airflow during the CF3R diagnostic visit, the installing contractor must correct the defect before the rater can sign and register the certificate. The city building inspector will not issue a final building sign-off or Certificate of Occupancy until all verified CF3R forms are registered in the state database.