Does a preapproved ADU plan come with its Title 24 report?

Do not assume it does. HCD notes that preapproved plans must be valid within the current triennial code cycle, and the certificate of compliance names your project and its location, with the climate zone taken from your address. Ask whoever published the plan what energy documents exist, and confirm with your building department what it needs for your lot.

Who hires the ECC-Rater for an ADU?

The builder or the owner. On an HVAC changeout, the installing contractor may hire the rater only if the homeowner authorises it. The rater must be independent of the builder and of the installer whose work is being tested.

Can my ADU share the main house's furnace?

Not through a shared ducted system. The Mechanical Code does not allow return air from one dwelling unit to be discharged into another, and the Energy Commission confirms that an existing furnace with a central return cannot be extended to serve an attached ADU conversion. The unit needs its own thermostat; systems without ducts are an option.

Does a garage conversion ADU need ECC testing?

Only for measures that require it, and a new heat pump serving the unit is one: refrigerant charge verification applies to heat pumps in every climate zone. The CF1R lists the items in its ECC section. A conversion does not need solar, because it is an addition.

Building Your First ADU: Title 24 for Homeowners

Your ADU's energy paperwork follows from one early decision, how the unit is built, and then runs in a fixed order: a CF1R at plan check, installer certificates during construction, ECC tests where the design needs them, and a final inspection that checks it all.

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A first ADU usually begins with a sketch and a question about size or setbacks. The energy side surfaces later, yet it decides the unit's heating, whether panels go on its roof, and how many site visits precede sign-off. This guide follows an owner's path from idea to move-in, and points to the detailed page for each type of unit.

Planning rules first, energy rules second

Whether you may build an ADU, and how big, is state ADU law (Gov. Code, §§ 66310–66342): HCD enforces it and your city applies it. How the unit is built falls under Title 24, whose Part 6 is the Energy Code. HCD counts planning departments, building departments, utilities and special districts among the agencies that review an ADU permit (Gov. Code, § 66313, subd. (k)). Review is ministerial, without a hearing, and the agency has 15 business days to say in writing whether your application is complete (Gov. Code, § 66317, subd. (a)(2)(A)). The zoning limits have a page of their own.

Many cities now publish preapproved ADU plans. AB 1332 (Chapter 759, Statutes of 2023) required local agencies to set up a preapproval program by 1 January 2025, and a detached ADU built from a preapproved plan must be approved or denied within 30 days. HCD adds that such plans must be valid within the current triennial code cycle, which for an application made today means the 2025 code. Expect energy documents prepared for your lot all the same: Part 1, § 10-103(a)1A ii, ties each certificate to a named project and location, and the climate zone follows your address.

Step 1: settle what kind of ADU it is

The Energy Code has no ADU category. It classifies the unit by how it is built:

Freestanding and new: a newly constructed building, treated as a new single-family home, even with a breezeway linking it to the house (SFCM Figure 9-4). See detached ADUs.
Attached by a shared wall, floor or ceiling, or stacked as a second storey on an existing detached garage: an addition under § 150.2(a). See attached ADUs and ADUs above a garage.
A converted garage or storage building that becomes conditioned for the first time: also an addition. See garage conversions.
Carved out of space already conditioned, such as a conditioned basement or pool house: an alteration under § 150.2(b). A JADU usually falls here.

Use these same words on the order and on the permit application. A unit drawn as one type and documented as another invites a correction.

Step 2: three owner decisions

Heating and cooling. The unit needs its own thermostat, and CMC 311.4 bars return air from one dwelling unit being discharged into another, so it cannot borrow the house's ducted furnace; ductless systems are an option (SFCM p. 9-10). A new detached unit is measured against a heat pump baseline (§ 150.1(c)6).
Water heating. New construction expects a heat pump water heater, though a new dwelling unit of 500 square feet or less may use an electric heater with point-of-use distribution, and a unit with one bedroom or fewer may use a 120-volt heat pump model (§ 150.1(c)8).
Windows. Their U-factor and SHGC feed the model, so pick the product line early.

The drawings to send are listed under what plans an ADU report needs.

Step 3: solar, if the unit is new and detached

A newly constructed detached ADU needs a newly installed PV system unless an exception applies (§ 150.1(c)14). Panels already on the main house do not count by themselves, but new modules added to that array on the same lot do, provided they are part of the ADU permit and the utility lets the system grow. Conversions and additions are outside the requirement (§ 150.2(a), Exception 6). Sizing and exceptions: does an ADU need solar.

Step 4: the permit, then the ECC visits

The CF1R goes in with your permit set, registered first with an ECC-Provider if anything needs field verification, and the department approves it before issuing the permit. Field verification is done by an ECC-Rater, the role that was called a HERS rater until it was renamed on 1 January 2026. You or your builder hire the rater, who must be independent of the installers. For a heat pump in a new unit, the list typically runs to refrigerant charge, minimum airflow and rated heating capacity, plus duct leakage and fan efficacy (watts per cfm) when ducted. A vented range hood has its certification, airflow and sone rating checked (§ 150.0(o)2B), and a new detached unit usually adds quality insulation installation, recorded on CF3R-ENV-21-H at framing and CF3R-ENV-22-H once insulation is in.

The rater cannot sign a CF3R until the installer's CF2R is registered, and a failed test means a correction and a retest. After delivery walks through each visit.

Step 5: final inspection and move-in

At final, installed work is checked against the approved set, with every CF2R and CF3R complete and registered. Copies of each, with operating and maintenance information, stay in the unit for you (§ 10-103(b)); file them with your property records.

Where first-time owners lose time

Swapping the heat pump or windows after the report. Any swap that may break compliance needs re-approval on amended paperwork (§ 10-103(a)2B).
Counting on the house's panels. Only newly added modules satisfy the solar rule.
Unpermitted space. A garage converted years ago without a permit is assessed under the code in force when you apply, and the department decides whether it complies as new construction or as an addition. For an unpermitted ADU built before 1 January 2020, Gov. Code § 66311.7 limits when a permit can be refused for violating building standards. See unpermitted work.

Still choosing who prepares your report? See how to choose a Title 24 consultant.