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Building Code Reference

Got a Title 24 150.0(m) correction?

Duct sealing and insulation

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

Title 24 Section 150.0(m) is the California energy code requirement for duct sealing and insulation on residential HVAC systems. It sets minimum R-values for supply and return ducts located outside conditioned space and requires those ducts to be sealed to prevent conditioned air from leaking into attics, crawl spaces, and wall cavities. Compliance is verified by a certified ECC-Rater (Energy Code Compliance rater, formerly HERS) who performs a duct leakage test before walls are closed up. Single-family and multifamily projects with new or replaced duct systems nearly always trigger this section.

How to fix it

  1. Add a duct insulation R-value note to the mechanical schedule

    On your mechanical plans, update the duct schedule to explicitly state the R-value for all ducts in unconditioned space. Under Title 24 Part 6, supply and return ducts need at least R-6.0 (150.0(m)1B), and the prescriptive package (Table 150.1-A, Option B) calls for R-8 in most climate zones. Do not use a generic 'insulate per code' note. Write the actual number (e.g., 'Duct insulation: R-8 minimum on all attic supply runs'). If you're not sure which climate zone applies, look at the CF1R certificate or check the CEC's climate zone map for the project address.

  2. Specify the sealing method by name on the plans

    Plans need to call out how ducts will be sealed, not just that they will be sealed. Acceptable methods under CMC 603.1 and Title 24 150.0(m) include: mastic sealant (the most common field-applied option), fiberglass mesh tape with mastic, or UL 181-listed aluminum foil tape. Standard fabric duct tape does not qualify — it degrades over time. Add a note on the mechanical plan sheet: 'All duct joints and seams to be sealed with mastic sealant or UL 181 listed tape at all transverse joints, longitudinal seams, and connections.'

  3. Include the ECC duct leakage test requirement on plan notes

    Plan-checkers need to see that an ECC duct leakage test (the ECC program replaced HERS) is required as a condition of final. Add a note to your mechanical plans: 'Duct leakage testing by a certified ECC-Rater is required per Title 24 Section 150.0(m)11 prior to final inspection.' Confirm that the CF1R document on file with the building department lists the duct leakage test as a required verification measure. The CF1R is generated by your Title 24 energy compliance software. If the test isn't checked in the software, it won't show up on the certificate, and the plan-checker has no way to verify it.

  4. Clarify the scope of new versus existing duct runs on the drawings

    If you're adding duct runs to an existing system, your plans need to clearly show which duct segments are new and which are existing-to-remain. Mark new ductwork with a heavy solid line and existing ductwork with a dashed line (or use a legend). This lets the plan-checker confirm which sections are subject to 150.0(m). Ambiguous drawings are one of the fastest ways to trigger a second corrections round. The city can't assume what's new and what's not, so they'll default to flagging everything.

  5. Schedule the ECC-Rater before drywall

    Once your plans pass, coordinate with a certified ECC-Rater before you close up the walls and ceiling. The duct leakage test requires the ducts to be accessible. Some raters need to see the duct connections before insulation is blown in. Testing typically takes a few hours on a residential project. The rater registers the results on the Certificate of Verification (CF3R) with an ECC-Provider data registry, and the city checks the registered CF2R and CF3R at final. If you close up before the test, the city may require you to open the wall back up, which adds cost and days to the job.

  6. Resubmit with corrected mechanical plans and an updated CF1R

    When you're ready to resubmit, include: (1) updated mechanical plans showing R-values, sealing method, and ECC test note; (2) an updated CF1R from your energy compliance software reflecting the duct leakage test requirement; (3) a response letter listing each correction item and how it was addressed. Correction letters are numbered, so match your response to those numbers. A clean resubmittal with organized responses moves faster through the review queue.

  7. Confirm climate zone R-value requirements with your energy consultant

    Title 24 Part 6 duct R-value requirements vary by climate zone. California has 16 climate zones and the required R-value for attic ducts differs across them. If you're working in multiple jurisdictions, don't assume the same number applies everywhere. Your Title 24 energy consultant or the CEC's compliance software will give you the correct value for each project. Getting it wrong on the plans means a correction; getting it wrong in the field means a failed ECC test and a reopened wall.

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Why you got flagged

Here's why plan-checkers flag 150.0(m) corrections. It usually comes down to one of four scenarios.

The most common is a missing ECC verification note. Your mechanical plans show a new furnace and duct system, but there's no call-out on the plans or the CF1R certificate saying the ducts will be ECC-tested for leakage. Plan-checkers aren't going to assume the contractor will handle it. They need to see it committed on the drawings before they sign off. Without that note, the correction goes out and your job sits.

The second scenario is duct insulation underspecified. Ducts in unconditioned attics need to meet a minimum R-value under the current adopted edition of Title 24 Part 6. If your mechanical schedule just says "insulate ducts per code" with no R-value called out, that's a correction. Plan-checkers want the actual number on the plans, not a generic reference.

Third is duct sealing method not documented. Saying "seal ducts" is not enough. The plans need to specify that sealing will be done with mastic, mastic tape, or UL 181 listed tape — not standard cloth duct tape, which fails over time. If the sealing method is missing or vague, expect a correction citing 150.0(m) along with CMC 603.1.

Fourth is scope creep on existing systems. You're permitted for a bathroom addition, but you're extending the duct system to serve the new room. The moment new duct runs are added, 150.0(m) applies to the new runs, sometimes to the whole system depending on how the city reads the scope. This surprises a lot of contractors who didn't realize a small extension triggers ECC testing.

The official code

California Energy Commission — Title 24 Part 6 Building Energy Efficiency Standards

Read the source →

Common questions

Does Title 24 150.0(m) apply to HVAC replacements, or only new construction?
It applies to both, but the scope depends on what you're changing. If you're replacing just the furnace or air handler and leaving the existing duct system in place, the existing ducts may not be subject to 150.0(m) unless the city treats the alteration as a new installation. But if you're replacing or adding any duct runs, those new segments are subject to the full section including R-value requirements and ECC duct leakage testing. The safest approach is to call the building department before you pull the permit and ask how they scope it for replacements, because interpretations vary by city.
What R-value do I need for attic ducts under Title 24 150.0(m)?
The required R-value depends on your climate zone and the duct location. Under the 2025 Title 24 standards, Section 150.0(m) sets a mandatory minimum of R-6.0 for supply and return ducts, with a reduced R-4.2 allowed in an unvented attic that meets the listed conditions. The prescriptive package (Table 150.1-A, Option B) calls for R-8 attic ducts in most climate zones. Don't rely on memory or a prior project's notes. Pull the CF1R for the current project from your energy compliance software and confirm the required value for that specific climate zone. If you're working in a climate zone you don't normally cover, your Title 24 consultant can run the numbers quickly.
What is an ECC duct leakage test and when does it happen?
An ECC duct leakage test is a pressure test of your duct system performed by a certified ECC-Rater (Energy Code Compliance rater, formerly HERS). The rater pressurizes the duct system using a blower and measures how much air escapes at unsealed connections. Under Title 24 150.0(m), the test must be passed before final inspection. It typically happens after ductwork is installed but before drywall goes up and insulation is blown in, so the rater can access the joints if repairs are needed. The rater completes and registers a Certificate of Verification (CF3R) through an ECC-Provider data registry, which the city uses to verify compliance at final.
Can I use duct tape to seal ducts and pass an ECC test?
No. Standard fabric duct tape (the gray kind) is not an approved sealing method under Title 24 150.0(m) or CMC 603.1. It loses adhesion over time, especially with temperature cycling in an attic. Approved methods are mastic sealant, fiberglass mesh tape embedded in mastic, or UL 181-listed metallic tape. Mastic is the most field-proven option and is what ECC-Raters and inspectors are used to seeing. If a rater finds fabric duct tape at any joint during testing, they'll fail the installation and you'll need to re-seal before they can test again.
Does 150.0(m) apply to mini-split systems with no ducts?
No. Title 24 Section 150.0(m) covers ducted HVAC systems. Ductless mini-split systems don't have supply or return ductwork running through unconditioned space, so 150.0(m) doesn't apply. That said, mini-splits have their own Title 24 compliance requirements covering efficiency ratings and refrigerant charge verification, which are addressed in other sections of the energy code. If you're switching from a ducted system to a ductless system, make sure your CF1R is updated to reflect the change in system type.
What if the ECC-Rater finds duct leaks during testing?
The rater will note the failing locations and you'll need to re-seal before they can issue a passing Certificate of Verification (CF3R). They don't fail the whole job on one small leak. They'll point out which joints or connections need attention and give you time to fix them before retesting. Common problem spots are at register boots, at the air handler connection, and at takeoff collars from the main trunk. Having mastic and a brush on site when the rater shows up is standard practice. A re-test usually adds a few hours to the day, not a whole separate visit, depending on your rater's schedule.

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