Accessory dwelling units are one of the most flexible ways to add living space and value to a California property, but they must meet the same energy rules as any new home. Title 24, California’s Energy Code, sets the baseline for how efficient your ADU needs to be.
If you plan carefully, you can go beyond bare minimum compliance and create a net-zero ready unit that is comfortable, affordable to run, and future proof.
This guide walks through what Title 24 means for ADUs, how to design for net-zero readiness, and practical steps to stay compliant without breaking your budget.
Understanding Title 24 and Its Impact on ADUs
Title 24 is a set of building energy efficiency standards that applies to most new residential construction in California, including detached ADUs, attached ADUs, and many garage conversions. For ADUs, the most relevant part is Title 24, Part 6, which governs the building envelope, HVAC, water heating, lighting, and renewable energy.
A few key points about how Title 24 affects ADUs:
- Most newly built or significantly altered ADUs must comply. New detached units, attached additions, and major garage conversions that create conditioned living space will trigger Title 24 review.
- You can comply using a prescriptive or performance path.
- The prescriptive path follows a checklist of minimum insulation, window, HVAC, and lighting requirements.
- The performance path uses energy modeling software to show that your proposed ADU uses no more energy than a reference design, which gives more flexibility on materials and systems.
- Climate zones matter. California is divided into climate zones with different baseline requirements for insulation, windows, and mechanical systems. An ADU in Los Angeles will have different targets than one in the Sierra foothills.
- Mechanical ventilation and indoor air quality are mandatory. Even very small ADUs must provide adequate fresh air and exhaust, which usually means dedicated fans, a balanced ventilation system, or continuous local exhaust.
Actionable steps at the planning stage:
- Involve a Title 24 consultant early, ideally at schematic design, instead of waiting until permit submittal.
- Tell your designer and contractor that your goal is a net-zero ready ADU, not just “passing Title 24.”
- Confirm up front whether your ADU is classified as new construction, an addition, or a conversion, since this affects solar and other requirements.
The Path to Net-Zero: What It Means for Your Accessory Dwelling Unit
A true net-zero energy home produces as much energy over a year as it consumes, usually by combining high efficiency with on-site solar. A net-zero ready ADU is built efficient enough that a modest solar and storage system can offset its annual energy use once you decide to install it.
Designing for net-zero readiness in an ADU focuses on four pillars:
- Tight, well insulated envelope
- Upgrade wall, roof, and floor insulation beyond code minimums where feasible.
- Use high performance windows with low U-factors and low solar heat gain where appropriate.
- Pay attention to air sealing around penetrations, top plates, and rim joists or slab edges.
- High efficiency HVAC and water heating
- Favor all-electric systems such as mini split heat pumps and heat pump water heaters.
- Right size equipment rather than oversizing, since ADUs often have small loads.
- Design efficient duct layouts or consider ductless systems to avoid energy losses.
- Low lighting and plug loads
- Use all LED luminaires and smart controls.
- Select ENERGY STAR appliances and induction cooking where layout allows.
- Plan for smart plugs or load management to control miscellaneous electronics.
- Solar and storage readiness
- Reserve roof area with good sun exposure for future photovoltaic panels.
- Design electrical panels, conduit, and wall space to accommodate a future battery and EV charger.
Net-zero readiness is as much about design discipline as it is about technology. The more efficiency you bake into the building fabric and systems, the smaller and more affordable the solar and storage system needs to be later.
Key Title 24 Requirements for New and Existing ADUs
While every project is unique, most ADU designs must address the same core Title 24 categories.
Building envelope and insulation
- Walls and roof assemblies must meet or exceed minimum R-value requirements for your climate zone. In many cases, continuous exterior insulation or advanced framing can help reduce thermal bridging.
- Slab or floor assemblies may require insulation at the perimeter or below the slab, especially for heated spaces.
- Windows and doors are limited by maximum U-factor and solar heat gain values. Larger glass areas, especially on west facing walls, may require better performing products to maintain compliance.
Practical tips:
- Coordinate window sizes and locations with your energy consultant instead of changing them late in design.
- Consider shading devices or deep overhangs on large glass areas to reduce cooling loads.
HVAC and ventilation
Title 24 sets minimum efficiency ratings for heating and cooling equipment and requires mechanical ventilation in dwelling units.
- Use high efficiency heat pump systems for heating and cooling whenever possible.
- Provide continuous or demand controlled ventilation, either through dedicated fans or a balanced system such as an ERV or HRV.
- If you use ducted systems, ducts must be sealed, tested, and often located within conditioned space or well insulated.
Water heating
Water heaters are a major energy use in small units, so Title 24 strongly favors efficient options.
- Heat pump water heaters are often the easiest path to compliance for new ADUs, especially all-electric designs.
- Short, well insulated hot water runs and central locations reduce wasted heat and wait times.
- Recirculation systems, if included, must use efficient controls.
Lighting and controls
Title 24 requires high-efficacy lighting and specific control strategies:
- Practically all permanent fixtures in an ADU should be high efficacy LED.
- Certain spaces must use occupancy or vacancy sensors.
- Outdoor fixtures attached to the building need high efficacy sources and appropriate controls, such as photocells or time clocks.
Solar and storage readiness
Most new detached ADUs are now brought under California’s solar requirements, while many conversion or attached units may qualify for exemptions. In addition, new dwelling units must typically be “energy storage system ready,” which means providing space and wiring pathways so a battery can be added later.
An experienced ADU contractor can help interpret which rules apply to your specific project type and jurisdiction.
Step-by-Step Guide: Designing Your ADU to Meet Title 24 Standards
Think of Title 24 compliance and net-zero readiness as a process, not a one time checklist.
Step 1: Define goals and budget
- Decide whether you want to meet minimum code, significantly exceed it, or pursue a formal net-zero or high performance program.
- Set a realistic budget line item for energy upgrades, including better windows, additional insulation, and more efficient mechanical systems.
Step 2: Coordinate early with your design and energy team
- Engage a designer or architect who has completed ADUs under the current code cycle.
- Hire a Title 24 consultant or energy modeler early and share your goals.
- Review climate zone specific strategies such as shading, natural ventilation, and roof reflectivity.
This is also the ideal stage to think about the look and feel of the space. For style inspiration that still respects a high performance envelope, browse our roundup of the latest ADU design trends in West Hollywood.
Step 3: Iterate the design with energy modeling
- Have your energy consultant run a preliminary model as soon as you have a basic floor plan, window schedule, and massing.
- Adjust window sizes, orientations, insulation levels, and system choices to find a cost effective path that still meets your comfort and sustainability targets.
- Decide whether you will follow the prescriptive package or a performance based approach.
Step 4: Finalize construction documents and Title 24 forms
- Once the design is set, your Title 24 consultant will prepare formal compliance documentation for permit submittal.
- Make sure your builder understands the assumptions in those documents, such as insulation types, duct locations, or equipment efficiencies.
- Coordinate with your local jurisdiction to understand any additional green building or reach code requirements beyond the state minimum.
Step 5: Build with verification in mind
- Choose contractors familiar with airtightness detailing, high performance windows, and heat pump systems.
- Plan for required testing and inspections, including duct leakage tests, fan flow tests, or other field verifications.
- Keep product submittals and manuals organized so inspectors can easily confirm that installed equipment matches the compliance documentation.
Step 6: Operate and optimize
- Once your ADU is occupied, educate residents on how to use controls, thermostats, and ventilation systems correctly.
- If you install solar and storage, use monitoring tools to understand energy patterns and make small adjustments that move you closer to net-zero performance.
Cost Considerations and Incentives for Building a Net-Zero Ready Unit
Designing an ADU that is net-zero ready usually costs more upfront than a code minimum unit, but the premium is often smaller than people expect, especially when you take advantage of incentives.
Typical extra costs might include:
- Higher performance windows and additional insulation
- Upgrading from a traditional gas furnace and tank water heater to heat pump systems
- Prewiring and panel upgrades for future solar, storage, and EV charging
- Larger or additional roof area optimized for solar
These investments are offset over time by lower utility bills and higher property value, particularly as California continues to tighten energy standards.
Homeowners planning an ADU should also explore:
- Federal tax credits for residential clean energy, which can reduce the net cost of qualifying solar and battery systems.
- Statewide heat pump incentives, which offer rebates for heat pump HVAC and water heaters installed by participating contractors.
- Self Generation Incentive Program (SGIP) and utility specific rebates that help pay for battery storage and other clean energy technologies.
- Local utility programs, such as bill credits or rebates for efficient water heaters, insulation, or smart thermostats.
Because programs and amounts change frequently, it is smart to ask your contractor to help coordinate incentive applications as part of the project scope.
The Role of Renewable Energy in Achieving Compliance (Solar and Beyond)
For many ADUs, solar photovoltaic systems are either required or strongly recommended to meet Title 24 targets and move toward net-zero performance.
Key considerations:
- Know whether your ADU triggers the solar mandate. New detached ADUs commonly must meet solar requirements, while attached ADUs, internal conversions, and junior ADUs may be exempt.
- Right size the system. California’s energy code sets minimum solar sizing formulas based on conditioned floor area and climate zone, but you can choose to install more capacity if you want to cover additional loads such as EV charging or future electrification.
- Plan for shading and roof layout. Preserve unshaded roof planes with good solar access, avoid unnecessary penetrations, and coordinate mechanical equipment so it does not compete for the same space.
- Design for storage readiness. Even if you do not install a battery on day one, Title 24 ESS ready rules often require setting aside wall space and installing conduit and breakers so that storage can be added later with less disruption.
Beyond solar and batteries, you can integrate other renewable or low carbon strategies, such as high performance envelopes, heat pumps, and induction cooking, which indirectly reduce the amount of solar needed to achieve net-zero performance.
Troubleshooting Common Challenges When Upgrading or Building an ADU Under Title 24
Even well planned projects can run into obstacles. Here are some of the most common and how to address them.
Challenge: Converting an older, uninsulated garage
- Solution: Budget for structural upgrades and full envelope improvements, not just finishes. Add continuous exterior insulation where possible, insulate and air seal the roof assembly carefully, and replace old garage doors with proper walls and high performance windows.
Challenge: Limited electrical capacity
- Solution: Coordinate early with your designer, electrician, and utility. A load calculation can show whether you truly need a panel or service upgrade. When you do, time it with other electrical work to minimize delays and cost, and consider future EV charging and storage.
Challenge: Meeting ventilation and IAQ requirements in a small footprint
- Solution: Use compact, quiet fans or a small balanced ventilation unit that can serve the entire ADU. Plan locations so they are accessible for maintenance and do not compromise acoustics or layout.
Challenge: Budget pressure during construction
- Solution: Protect the high value energy efficiency measures in your budget, such as envelope quality, heat pumps, and solar readiness. If you must cut costs, consider deferring noncritical finishes rather than downgrading key performance elements that are very difficult to change later.
Challenge: Interpreting plan check comments on Title 24 forms
- Solution: Have your Title 24 consultant respond directly to energy related comments. Small clarifications early can prevent rework in the field. Make sure all substitutions are reviewed so they do not accidentally break compliance.
Making Your Next Step Toward a Net-Zero Ready Accessory Dwelling Unit
Title 24 is not just a set of hoops to jump through. For ADU owners, it is a roadmap to quieter, more comfortable, and more resilient living spaces that hold their value as codes and energy prices evolve. By combining smart envelope design, efficient systems, and renewable energy readiness, you can create an ADU that is both code compliant and net-zero ready.
FTR Renovation & Build specializes in guiding California homeowners through this process, from early design decisions to final inspections. With the right team and a clear plan, your ADU can meet today’s standards and be ready for tomorrow’s clean energy future.