Does my ADU need a QII insulation inspection under Title 24?

It depends on the project type and size. A newly constructed ADU that follows the prescriptive path needs Quality Insulation Installation (QII), with an ECC-Rater checking the insulation and air barrier. An ADU addition (attached unit or garage conversion) of 700 square feet or less is exempt from the prescriptive QII requirement, while larger additions need it, with a few allowances for converted spaces.

What QII is

QII is a field-verified check that insulation was installed without gaps, voids or compression, and that the building's air barrier is continuous. The criteria are in Reference Residential Appendix RA3.5. An ECC-Rater, the role formerly called a HERS rater, does the verification.

New detached ADUs

• Table 150.1-A lists QII as a prescriptive requirement in all 16 climate zones.
• QII isn't a mandatory measure, so the performance path can model the building without it. In its ADU training, though, the CEC notes that modeling without QII carries a significant penalty that is hard to make up elsewhere.
• If the performance model takes credit for QII, an ECC-Rater must verify it.

ADU additions, including garage conversions

• 700 square feet or less: under Section 150.2(a)1Bv, the QII requirements of Section 150.1(c)1E do not apply. The CEC's 2025 ADU FAQ adds that if QII is modeled for a compliance credit anyway, the ECC-Rater must verify it.
• Over 700 square feet: the addition follows Section 150.1(c), which includes QII. When the addition converts existing unconditioned space, such as a garage, Section 150.2(a)1Av relaxes two items: existing window and door headers don't have to be insulated, and air sealing isn't required where the existing air barrier isn't being removed or replaced.

Alterations

Converting space that's already conditioned is an alteration, and QII isn't part of the prescriptive alteration requirements. Altered assemblies still have to meet the insulation levels that apply to them.

Scheduling tips if QII applies

• The rater has to see the installed insulation and air barrier, so book the visit before drywall goes up. A missed visit can mean opening walls.
• Tell your insulation contractor early that the job is QII, so the crew installs to the RA3.5 criteria from the start.
• Make sure the CF2R installation certificate for insulation is completed and registered before the rater arrives.

What this means for your MEP plans and Title 24 report

The CF1R states whether QII is required or credited, and that becomes a construction requirement your builder must schedule. On small additions, we can often show compliance without QII. On new detached ADUs, it usually pays to include it rather than offset the penalty. Either way, the report tells you up front. See the ADU Title 24 guide, Title 24 reports, and common Title 24 plan check mistakes.

Sources: energy.ca.gov, energy.ca.gov, energy.ca.gov.