For general contractors building ADUs in California, Title 24 Part 6 (Building Energy Efficiency Standards) represents one of the most complex—and most commonly misunderstood—compliance requirements. While structural, plumbing, and electrical codes are relatively straightforward, Title 24 introduces performance-based calculations, climate-specific requirements, and mandatory third-party verification that can delay permits if not properly addressed.
Why GCs Need to Understand Title 24: Unlike other building codes where you can rely on "standard practice," Title 24 compliance requires climate-specific calculations, performance modeling using CEC-approved software, third-party verification through certified HERS raters, complete documentation submitted with permit applications, and field testing during and after construction.
In This Guide
- Understanding Title 24 for ADU Projects
- 2026 Code Changes: What's New
- Compliance Pathways Explained
- Mandatory Requirements Breakdown
- HVAC & Heat Pump Requirements
- Water Heater Specifications
- Battery Storage Ready (BESS) Requirements
- Building Envelope & Insulation Standards
- Lighting & Electrical Requirements
- HERS Testing & Field Verification
- Climate Zone Considerations
- Common Plan Check Corrections
- Required Documentation & Forms
- Cost Implications for GCs
- How to Avoid Permit Delays
Understanding Title 24 for ADU Projects
What is Title 24?
Title 24, Part 6 of the California Code of Regulations establishes minimum energy performance requirements for all new residential construction in California, including ADUs. Created following the Warren-Alquist Act of 1974, these standards are updated every three years by the California Energy Commission (CEC) to progressively reduce energy consumption and greenhouse gas emissions.
All ADUs Must Comply
Title 24 applies to:
- Detached backyard ADUs (new construction)
- Attached ADUs (additions to primary residence)
- Garage conversions (when creating new dwelling units)
- Junior ADUs (units under 500 sq ft within existing homes)
- Factory-built/modular ADUs
Even conversion projects trigger Title 24 requirements when installing new HVAC systems, water heaters, windows, or altering the building envelope.
Critical: A single missing form or incorrect calculation can result in plan check corrections that delay your project by weeks. Understanding Title 24 requirements upfront is essential for accurate cost estimating and realistic timelines.
2026 Code Changes: What's New
The 2025 Building Energy Efficiency Standards were adopted in September 2024 and took effect January 1, 2026. Any ADU project with permit applications submitted on or after this date must comply with the new code.
Key Changes Affecting ADU Construction
1. Expanded Heat Pump Requirements
The 2026 code significantly expands heat pump adoption as California moves toward building electrification. For newly constructed ADUs:
- Heat pumps are now the baseline for space conditioning calculations
- Traditional air conditioning replacements may require heat pump systems instead
- California's goal: 500,000 heat pump installations within the first three years
Impact for GCs: Plan for heat pump HVAC systems in all new ADU construction. Budget accordingly—heat pumps typically cost $3,000-$8,000 more than traditional AC units but provide both heating and cooling.
2. Battery Storage Ready (BESS-Ready) Requirements
New ADUs must now be "battery ready" under Section 150.0(s), meaning:
- Electrical panels must accommodate future battery storage systems
- Dedicated space and conduit for batteries must be provided
- Panels with 200-amp service require 225-amp busbar ratings
Exception: If the ADU's electric service is 125 amps or less, BESS-ready requirements do not apply.
3. Enhanced Ventilation Standards
The 2026 code strengthens indoor air quality requirements with new ventilation rate calculations and monitoring provisions, particularly for units under 500 sq ft.
4. Continued Solar Requirements
Solar photovoltaic requirements remain in effect for newly constructed ADUs, though specific sizing depends on climate zone, building orientation, and energy consumption modeling.
5. Electric Water Heater Provisions
For ADUs 500 sq ft or smaller with insufficient space for a 240V heat pump water heater (HPWH), Exception 1 to Section 150.1(c)8 allows installation of instantaneous electric water heaters with point-of-use distribution per Reference Residential Appendix RA4.4.5.
Projected Impact: According to the California Energy Commission, the 2026 standards are projected to save $4.8 billion in energy costs over time, reduce greenhouse gas emissions by 4 million metric tons, and increase construction costs by approximately 3-5% for typical ADUs.
Compliance Pathways Explained
California offers two methods for demonstrating Title 24 compliance. Understanding which path is appropriate for your project is critical for accurate bidding and successful plan check approval.
Prescriptive Compliance Method
How It Works
The prescriptive approach requires each individual building component to meet specific minimum or maximum values outlined in the code. Think of it as a checklist—every item must meet the standard.
Requirements Include:
- Minimum insulation R-values for walls, ceilings, and floors
- Maximum window U-factors and Solar Heat Gain Coefficients (SHGC)
- Specific HVAC equipment efficiency ratings (SEER, HSPF, EER)
- Mandatory water heater types (typically heat pump water heaters)
- Required duct sealing and insulation values
- Specific lighting efficacy minimums
When to Use Prescriptive
- Simple, straightforward ADU designs
- Standard rectangular floor plans
- Typical construction methods
- Projects where you want certainty without modeling
Example: A 600 sq ft detached ADU in Climate Zone 9 (Los Angeles) using prescriptive compliance must have: R-30 ceiling insulation, R-15 wall insulation, U-0.30 windows with SHGC ≤ 0.23, 16 SEER2 / 9.5 HSPF2 heat pump, Heat pump water heater (≥ 3.5 UEF), and LED lighting throughout.
Performance Compliance Method
How It Works
The performance approach uses CEC-approved software (CBECC-Res) to model your proposed ADU's energy consumption against a "standard design" baseline. If your design uses less energy than the standard, it complies—even if individual components don't meet prescriptive minimums.
Key Concept: Energy Budget
The software calculates an energy budget by creating a virtual version of your ADU with prescriptive-compliant components, then compares it to your actual design. You can "trade" better performance in one area for lesser performance in another, as long as total energy use stays within budget.
Example Trade-Offs Possible
- Install higher-efficiency windows → Use less expensive insulation
- Optimize building orientation → Reduce solar panel size
- Install premium HVAC system → Use standard water heater
- Add external shading → Allow larger window areas
| Factor | Prescriptive | Performance |
|---|---|---|
| Flexibility | Limited | Maximum |
| Modeling Cost | $0 | $800-$1,500 |
| Potential Savings | None | $2,000-$5,000 |
| Best For | Simple designs | Complex/unique projects |
Need Help with Title 24 Compliance?
Andalusia Drafting includes comprehensive Title 24 compliance with every ADU permit package. We handle all energy calculations, documentation, and HERS coordination.
Get a Free QuoteMandatory Requirements Breakdown
Regardless of whether you choose prescriptive or performance compliance, certain Title 24 requirements are mandatory for all ADU projects. These cannot be traded off or modeled away—they must be included in every design.
Section 110.2: Mandatory Equipment Requirements
HVAC Systems Must Include
- Thermostatic controls with setback capability
- Duct sealing verified by HERS rater (≤ 6% leakage for new construction)
- Minimum equipment efficiency ratings:
- Air conditioners: ≥ 15 SEER2, ≥ 11.5 EER2
- Heat pumps: ≥ 15 SEER2, ≥ 8.8 HSPF2, ≥ 11.5 EER2
- Furnaces: ≥ 80% AFUE (95% for weatherized)
- Refrigerant charge verification by HERS rater
- Airflow measurement by HERS rater
Water Heating Systems Must Include
- Minimum efficiency ratings:
- Heat pump water heaters: ≥ 3.5 UEF (most common for ADUs)
- Tank-type electric: ≥ 0.93 UEF
- Gas storage: ≥ 0.64 UEF
- Hot water pipe insulation (R-3 minimum)
- Recirculation systems (if installed) with controls and timer
Lighting Requirements
- High-efficacy light sources in all permanently installed fixtures
- Minimum efficacy: 65 lumens per watt for indoor, 45 for outdoor
- Motion sensors or vacancy sensors for certain applications
- Certified fixtures listed with CEC
Section 150.0: Mandatory Features and Devices
Building Envelope
- Vapor retarders where required by climate zone
- Air sealing at all penetrations, joints, and assemblies
- Verified air leakage ≤ 5 ACH50 (tested by HERS rater)
- Insulation installation verification by HERS rater
- Windows must have labels showing U-factor and SHGC
Ventilation
- Mechanical ventilation meeting ASHRAE 62.2 requirements
- Continuous or intermittent ventilation systems
- Exhaust fans in kitchens (100 CFM) and bathrooms (50 CFM)
- Whole house fans for certain climate zones and ADU sizes
HERS Verification Required: All ADU projects require third-party verification through a certified HERS rater for: duct system leakage testing, air handler/furnace airflow measurement, refrigerant charge verification, building envelope air leakage, insulation installation, and fenestration (windows/doors). Cost: $400-$800 for a standard ADU.
HVAC & Heat Pump Requirements
The 2026 Title 24 update places significant emphasis on heat pump technology as California transitions toward all-electric buildings.
New Construction ADU Requirements
For all newly constructed ADUs, heat pumps are now the baseline assumption in energy calculations. While the code doesn't explicitly prohibit other systems, using anything other than a heat pump makes compliance significantly more difficult and expensive.
Minimum Heat Pump Specifications (2026)
- SEER2: ≥ 15 (Seasonal Energy Efficiency Ratio, cooling)
- HSPF2: ≥ 8.8 (Heating Seasonal Performance Factor, heating)
- EER2: ≥ 11.5 (Energy Efficiency Ratio, steady-state cooling)
Common Heat Pump Types for ADUs
| Type | Best For | Typical Cost | HERS Testing |
|---|---|---|---|
| Mini-Split Systems | Small ADUs (400-800 sq ft) | $3,500-$6,500 | Refrigerant charge only |
| Multi-Split Systems | Larger ADUs (800-1,200 sq ft) | $6,000-$10,000 | Refrigerant charge per head |
| Ducted Heat Pump | Complex layouts, high ceilings | $8,000-$14,000 | Duct leakage, airflow, charge |
Ductwork Requirements
If your ADU uses a ducted HVAC system, ductwork must meet strict standards:
- All ducts in unconditioned spaces must be insulated to R-8 minimum
- Joints and seams sealed with mastic or approved tape (no duct tape)
- Maximum allowable leakage: 6% of total system airflow
- Testing performed at rough inspection before drywall
Pro Tip: For garage conversions, mini-split systems often provide the most cost-effective compliance path, avoiding duct testing requirements entirely.
Water Heater Specifications
Water heating represents approximately 20% of residential energy use, making it a critical component of Title 24 compliance. The 2026 code strongly favors electric heat pump water heaters (HPWHs) for all new ADU construction.
Mandatory Water Heater Requirements
For newly constructed ADUs using the prescriptive compliance method, heat pump water heaters are mandatory under Section 150.1(c)8.
Heat Pump Water Heater Specifications
- Minimum Uniform Energy Factor (UEF): ≥ 3.5
- Must be NEEA Advanced Tier certified
- Typical tank size for ADUs: 40-50 gallons
- Requires 240V electrical service
- Installation cost: $2,500-$4,000 installed
Exception for Small ADUs (≤ 500 sq ft)
Section 150.1(c)8 Exception 1 provides relief for very small ADUs where space for a traditional HPWH is limited:
- ADU must be ≤ 500 square feet
- Insufficient space for 240V heat pump water heater installation
- Must install instantaneous electric water heater (tankless)
- Must use point-of-use distribution per Reference Appendix RA4.4.5
- All hot water fixtures within 10 feet of water heater
HPWH Installation Requirements
- Space: Minimum 750 cubic feet of surrounding air space (1,000+ for optimal efficiency)
- Drainage: Condensate drain to approved location, drain pan required
- Temperature: Operates efficiently in 40°F-90°F ambient temperatures
- Electrical: Dedicated 30-amp, 240V circuit required
- Noise: 40-50 dB (similar to refrigerator)
Battery Storage Ready (BESS) Requirements
One of the significant new requirements in the 2026 Title 24 code is making newly constructed ADUs "battery ready" to support California's goals for energy storage and grid resilience.
What Does "Battery Ready" Mean?
Battery Energy Storage System (BESS) ready requirements don't mandate installing a battery—they require making your ADU ready for future battery installation without major electrical system modifications.
When BESS-Ready Requirements Apply
- Mandatory for: All newly constructed detached and attached ADUs with electrical service greater than 125 amps
- Exempt: ADUs with 125-amp service or less, conversion projects, Junior ADUs under 500 sq ft
Section 150.0(s) Requirements
Electrical Panel Requirements
The electrical panel must have a busbar rating greater than or equal to the panel's main breaker rating plus 25 amps.
- Option 1: 200-amp panel with 225-amp busbar (most common)
- Option 2: 150-amp panel with 200-amp busbar
- Busbar rating must be clearly marked on the panel
- Incremental cost: $100-$150
Dedicated Battery Space
- Minimum dimensions: 3 feet wide × 2 feet deep × 4 feet high
- Cannot be occupied by other equipment or storage
- Acceptable locations: garage, mechanical room, exterior wall with weather protection
- Must be labeled: "Reserved for Future Battery Energy Storage System"
Conduit Pathway
- Minimum 1-inch diameter conduit from main panel to battery space
- Must be continuous and properly supported
- Installed during rough electrical (before drywall)
- Cost: $250-$550 total
Building Envelope & Insulation Standards
The building envelope—walls, roof, windows, doors, and foundation—is critical to Title 24 compliance. Proper insulation and air sealing directly impact energy performance, HERS testing results, and long-term operating costs.
Prescriptive Insulation Requirements
Ceiling/Attic Insulation
| Climate Zone | Minimum R-Value |
|---|---|
| Zones 1-9 | R-30 |
| Zones 10-16 | R-38 |
Wall Insulation
| Framing | Minimum R-Value |
|---|---|
| 2×4 Framing | R-15 or R-13 + R-5 continuous |
| 2×6 Framing | R-21 or R-19 + R-5 continuous |
Window Requirements
| Climate Zone | Max U-Factor | Max SHGC |
|---|---|---|
| 6, 9 (LA area) | 0.30 | 0.23 |
| 10 (Inland Empire) | 0.30 | 0.23 |
| 12 (Sacramento) | 0.30 | 0.23 |
| 13, 14 (Bay Area) | 0.32 | 0.25 |
| 15, 16 (Mountains/Desert) | 0.30 | 0.40 |
Critical: Every window must have an NFRC (National Fenestration Rating Council) label showing U-Factor and SHGC. HERS rater will verify labels during inspection. Missing labels = failed inspection.
Air Sealing Requirements
Air leakage is a mandatory Title 24 requirement verified by HERS testing. Poor air sealing is a leading cause of HERS test failures.
Maximum Allowable Leakage: 5.0 ACH50
HERS rater will pressurize the ADU with a blower door to 50 Pascals and measure how much air leaks out.
Critical Air Sealing Locations
- Top and bottom plates: Seal to drywall/sheathing with foam or caulk
- Penetrations: All electrical boxes, plumbing, HVAC registers
- Window/door rough openings: Spray foam around entire opening
- Band joists: Spray foam or rigid foam + caulk
- Attic access hatches: Weatherstripping around perimeter
- Recessed lighting: Use IC-rated, airtight cans
Cost of Air Sealing: Materials $200-$400, labor $500-$1,000. Cost of Failed Test: Re-test fee $250-$400, corrections $300-$800, project delay 1-2 weeks. Total cost of failure: $550-$1,200 plus delays.
Lighting & Electrical Requirements
Lighting represents approximately 10-15% of residential energy use. Title 24 mandates high-efficacy lighting throughout ADUs.
Minimum Efficacy Standards
- Indoor lighting: 65 lumens per watt minimum
- Outdoor lighting: 45 lumens per watt minimum
- All lighting must be certified by California Energy Commission
Lighting Controls Required
- Bathrooms: Vacancy sensor OR occupancy sensor with manual override
- Closets/Storage: Vacancy sensor OR automatic shutoff after 15 minutes
- Outdoor Lighting: Photocell control OR astronomical time clock OR motion sensor
Recessed Lighting Requirements
- Must be IC-rated (Insulation Contact) if in insulated ceiling
- Must be airtight-rated for envelope air sealing
- LED integrated fixtures or LED-dedicated sockets
HERS Testing & Field Verification
HERS (Home Energy Rating System) testing is mandatory for all ADU projects and represents one of the most critical aspects of Title 24 compliance. Failed HERS testing is a leading cause of final inspection delays.
What is HERS Testing?
HERS testing is third-party verification performed by state-certified HERS raters to confirm that your ADU was built according to Title 24 specifications.
Mandatory HERS Verification Requirements
| Test | When | Standard | Cost |
|---|---|---|---|
| Duct System Leakage | Rough inspection | ≤ 6% of airflow | $150-$250 |
| Building Air Leakage | Final inspection | ≤ 5.0 ACH50 | $200-$350 |
| HVAC Airflow | Final inspection | 85-115% of design | Included |
| Refrigerant Charge | Final inspection | ±10% of target | $150-$250 |
| Insulation Quality | Rough inspection | No gaps/voids | $100-$200 |
Total HERS Testing Cost: $600-$1,050 for typical ADU
Common HERS Test Failures & How to Avoid Them
Failure #1: Duct Leakage (Most Common)
How to Pass: Use mastic (not duct tape) on all joints. Seal boot-to-register connections before drywall. Consider rigid metal ducts instead of flex. Have HVAC installer perform pre-test before calling HERS rater.
Failure #2: Air Leakage (Second Most Common)
How to Pass: Seal all penetrations as work progresses. Foam around all window/door rough openings. Caulk top plates to drywall. Use airtight recessed light fixtures. Pre-drywall air sealing walkthrough.
Failure #3: Refrigerant Charge
How to Pass: Use qualified HVAC installer familiar with HERS requirements. Follow manufacturer charging procedure exactly. Account for actual line set length in charge calculation. Allow system to run 15+ minutes before testing.
Climate Zone Considerations
California's 16 climate zones significantly affect energy requirements. The same ADU design in different zones requires different insulation values, window specifications, and equipment sizing.
Common Climate Zones for ADU Construction
| Zone | Areas | Heating Needs | Cooling Needs |
|---|---|---|---|
| 6 | San Diego coastal | Minimal | Low-moderate |
| 9 | Pasadena, Burbank, inland LA | Mild | Moderate |
| 10 | Riverside, San Bernardino | Moderate | High |
| 12 | Sacramento Valley | Moderate-high | Very high |
| 13 | Bay Area coastal | Moderate | Minimal |
| 16 | High desert/mountains | Very high | Moderate-high |
Cost Variation by Climate: The same 600 sq ft ADU costs $9,700-$14,000 for Title 24 compliance in Climate Zone 6 (San Diego), but $14,200-$20,500 in Climate Zone 16 (High Desert)—a difference of $4,500-$6,500.
Common Plan Check Corrections
Understanding the most frequent Title 24 plan check corrections helps avoid delays and resubmittals.
Top 10 Title 24 Plan Check Corrections
- Climate Zone Not Specified: Add prominent notation to title sheet
- Incomplete Building Envelope Information: Create insulation schedule with R-values for all assemblies
- HVAC Specifications Incomplete: Show SEER2/HSPF2/EER2 ratings (not old SEER)
- Water Heater Information Missing: Specify type, UEF rating, and location
- Title 24 Forms Missing: Include complete, signed CF-1R that matches plans
- Lighting Information Inadequate: Create fixture schedule with efficacy values
- BESS-Ready Requirements Not Shown: Show panel busbar rating and battery space
- Air Sealing Details Insufficient: Add details for critical locations
- Ventilation Requirements Not Addressed: Show exhaust fans and CFM ratings
- Solar Ready Requirements Not Shown: Show pathway from attic to panel
Cost of Plan Check Corrections: Direct costs $500-$1,100 per cycle. Indirect costs (delays, scheduling conflicts): $1,000-$3,000+. Multiple correction cycles can add 4-12 weeks to your timeline.
Required Documentation & Forms
Form CF-1R: Certificate of Compliance
Documents the proposed ADU design and demonstrates Title 24 compliance. Submitted with building permit application.
- Project information (address, climate zone, floor area)
- Building envelope specifications
- Mechanical systems details
- Water heating specifications
- Electrical and lighting information
- Must be signed by responsible party
Form CF-2R: Certificate of Installation
Verifies that equipment and materials were installed according to CF-1R specifications. Completed by installing contractors.
Form CF-3R: Certificate of Verification
Documents HERS rater field verification and testing results. Submitted directly to building department by HERS rater after final testing.
Important: CF-3R must be submitted before Certificate of Occupancy can be issued. Missing CF-3R can delay CO by weeks.
Cost Implications for GCs
Direct Title 24 Compliance Costs (600-800 sq ft ADU)
| Category | Cost Range |
|---|---|
| Energy Modeling & Documentation | $0-$500 |
| Building Envelope (insulation, windows, air sealing) | $2,400-$4,300 |
| Mechanical Systems (heat pump HVAC, HPWH, duct sealing) | $3,200-$6,500 |
| Electrical (BESS-ready, solar-ready) | $400-$850 |
| Lighting (LED fixtures, controls) | $250-$700 |
| HERS Testing | $600-$1,050 |
| Total | $6,850-$13,900 |
As Percentage of Construction Cost: 3.3-5.0% of total construction
Costs of Non-Compliance
- Duct Leakage Failure: $1,200-$2,650 (corrections + re-test + delays)
- Air Leakage Failure: $900-$2,150
- HVAC Performance Failure: $1,450-$3,100
- Plan Check Corrections (per cycle): $1,500-$4,100 (direct + indirect)
How to Avoid Permit Delays
Pre-Submittal Strategies
1. Engage Energy Consultant Early
Before plans are 50% complete. Cost: $200-$400. Savings: 2-4 weeks in plan check, $1,000-$3,000 in corrections.
2. Use Title 24 Compliance Checklist
Before permit submittal, verify:
- Climate zone clearly noted
- CF-1R complete, signed, matches plans exactly
- All insulation R-values specified
- All window U-factors and SHGC values shown
- HVAC equipment with SEER2/HSPF2/EER2 ratings
- Water heater type and UEF specified
- Lighting schedule with efficacy values
- BESS-ready compliance shown (if required)
3. Pre-Submittal Meeting with Building Department
For complex or unique projects. Cost: Your time (1-2 hours). Potential benefit: Eliminate entire correction cycle.
Construction Phase
Schedule HERS Rater Early
- Contact HERS rater 2 weeks before rough inspection needed
- Before official testing, do your own pre-check
- Consider informal pre-test service ($100-$200) to identify issues
Coordinate Final Inspections
- Day 1: Final HERS testing (all systems operational)
- Day 3-5: HERS rater submits CF-3R
- Day 5-7: Final building inspection (after CF-3R received)
- Day 7-10: Certificate of Occupancy issued
Let Us Handle Your Title 24 Compliance
At Andalusia Drafting, we include comprehensive Title 24 compliance with every ADU permit package. 100% compliant plans on first submittal, zero Title 24 corrections.
Get Your Free AssessmentKey Takeaways for General Contractors
- Title 24 is Mandatory and Enforced: No exceptions for ADUs. HERS testing is third-party verified. Failed tests delay Certificate of Occupancy.
- Upfront Planning Prevents Costly Delays: Engage energy consultant early. 80% of problems are preventable with proper planning.
- Professional Support Provides ROI: Investment in expertise returns 3-5X in time and money saved.
- Common Issues Are Predictable and Avoidable: Follow proven best practices. Train crews on quality installation. Pre-check work before formal testing.
- Documentation is Critical: CF-1R, CF-2R, CF-3R forms must be complete. Plans must match forms exactly.
Disclaimer: This guide provides general information about Title 24 requirements as of March 2026. Building codes and energy regulations are updated regularly. Always verify current requirements with local building departments and the California Energy Commission. This guide is for informational purposes and does not constitute professional engineering or legal advice. Consult qualified professionals for project-specific guidance.