Title 24 · California Energy Code

What duct insulation R‑values and labeling are required by climate zone?

Homes with ducts in unconditioned attics or crawlspaces must meet the minimum insulation shown in Table 150.2‑D (either R‑6 or R‑8 depending on climate zone). The R shown must be the insulation’s tested R at the actual installed thickness (wrap is assumed 75% of nominal; flex ducts use the (OD − nominal ID)/2 rule), flexible ducts must be labeled every 3 feet with that R, and insulation must be protected from weather and damage as required by the Code.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

The California Energy Code requires that ducts located in unconditioned spaces be insulated to a minimum R‑value that depends on the climate zone, as shown in Table 150.2‑D and implemented by § 150.0(m). For residential/multifamily work, the code also prescribes how to determine the installed thickness used to rate the R‑value, mandatory labels on flexible ducts, and basic protection requirements for the insulation per § 160.3(b)5D/E. All R‑values must be based on the insulation only (exclude air films, vapor retarders or other components) and be tested at the installed thickness per ASTM and certified as required by the Code.

The single most important rule: ducts in unconditioned spaces must meet the climate‑zone minimum R‑value in Table 150.2‑D, and the R shown must be the insulation’s tested R at the installed thickness (not including films or facers).

Requirements in detail

Which R‑value applies by climate zone (energy-code table)

Decision dimension Required minimum Code reference
Climate Zones 3, 5–7 (ducts in unconditioned spaces) R‑6 Table 150.2‑D; see § 150.0(m)
Climate Zones 1, 2, 4, 8–16 (ducts in unconditioned spaces) R‑8 Table 150.2‑D; see § 150.0(m)

Notes:

  • The Table above is the Code’s mandatory minimum for ducts in unconditioned space (Table 150.2‑D as implemented by § 150.0(m)).
  • The Code language explicitly ties the required R‑value to the insulation’s performance “as installed” and references ASTM test methods.

How the R‑value must be measured (testing and basis)

  • R‑values must be based on the insulation only (do not include air films, vapor retarders, facers, or other duct components). § 150.0(m) requires ASTM C518 or C177 test at 75°F mean temperature at the installed thickness and certification under Section 110.8.

How to determine installed thickness (affects the reported R)

Duct material / product type Installed thickness rule Code reference
Duct board, duct liner, factory‑made rigid ducts (not normally compressed) Use the nominal insulation thickness § 150.0(m)(d)
Duct wrap Assume 75% of nominal thickness (i.e., 25% compression) § 150.0(m)(d)
Factory‑made flexible air ducts Installed thickness = (actual outside diameter − nominal inside diameter) ÷ 2 § 150.0(m)(d)3

Labeling requirements for flexible duct products (multifamily/residential)

  • Insulated flexible duct products installed to meet the Code must include labels at maximum intervals of 3 feet showing the thermal performance R‑value for the insulation itself (again excluding air films and facers), and that R must be based on tests at the installed thickness. This labeling requirement applies for residential and multifamily per § 160.3(b)5D/E and related subsections.

Protection of insulation

  • Insulation must be protected from damage (sunlight, moisture, maintenance activities, wind). Insulation exposed to weather must be suitable for outdoor service (metal or other protective covering) or otherwise protected as specified by the Code. See § 160.3(b)5F and related protection language.

Exceptions & special cases

  • The Energy Code’s Table 150.2‑D gives a simple climate‑zone split (R‑6 vs R‑8) for ducts in unconditioned spaces. Other codes/tables (for example, the Mechanical Code Appendix tables) provide more granular R‑value requirements by duct location (exterior vs unconditioned vs indirectly conditioned) and by heating vs cooling service — consult the Mechanical Code Appendix if your project is covered by those mechanical provisions.
  • When altering an existing system: if more than 25 feet of new/replacement ducts are installed the altered ducts must meet the Section 150.0(m) provisions and Table 150.2‑D (the same R requirements apply) — see the altered‑duct subsections that reference Table 150.2‑D.
  • Some exceptions in the multifamily language relieve certain test/registry requirements for very large buildings (see exceptions to § 160.3(b)5K), but labeling/thickness definitions and R‑value testing requirements remain applicable. If your project is a large multifamily building check those exception lines carefully.

Common mistakes

  • Counting facers, vapor retarders or air films when claiming the R‑value. The Code requires the R of the insulation only, measured at installed thickness. Don’t include facers or air films in the R.
  • Using nominal thickness for wrap without applying the 75% installed‑thickness assumption when determining the R that must be reported. For wrap, the Code assumes 25% compression.
  • Forgetting to place labels every 3 feet on insulated flexible ducts (labels must show the tested R at installed thickness).
  • Applying the Table 150.2‑D R‑value without confirming whether the duct is in an unconditioned space or in a location covered by another table (mechanical code) — location matters.
  • Failing to protect outdoor‑exposed insulation from weather or sunlight as required.

Worked example — concrete scenario

Scenario: single‑family home in Climate Zone 8 with an air handler in an unconditioned attic and flexible insulated supply ducts.

  1. Required minimum: Table 150.2‑D requires R‑8 for ducts in Climate Zone 8. Use that R as the target. § 150.0(m) / Table 150.2‑D.
  2. Installed thickness: flexible duct installed thickness is measured as (OD − nominal ID) ÷ 2. If the flexible duct has nominal inside diameter 8.0 in and the actual outside diameter measures 9.0 in, installed thickness = (9.0 − 8.0) ÷ 2 = 0.5 in. Use the manufacturer’s ASTM‑tested R at that installed thickness to confirm whether the product meets R‑8. Do not add facer or air films to get the R.
  3. Labeling: the flexible duct product installed to meet the requirement must carry labels at maximum 3‑foot intervals that state the thermal performance R‑value for the insulation itself (based on the installed thickness testing). Installer must ensure labels are present and legible.
  4. Protection: because the attic may have roof vents or solar exposure, protect the insulation from sunlight and moisture per the protection requirements.

If the product’s tested R at the calculated installed thickness is less than R‑8, you must select a thicker/ higher‑R product (or move the ducts into conditioned space, or use another approved compliance approach).

Related provisions (quick list)

  • § 150.0(m) — Duct insulation R‑value definitions, installed‑thickness rules, test methods (ASTM) and general duct insulation provisions.
  • Table 150.2‑D — Minimum duct insulation R‑values by climate zone (R‑6 / R‑8 split) (referenced by § 150.0(m)).
  • § 160.3(b)5D/E — Installed thickness, labeling (max 3 ft intervals) and protection requirements for insulated flexible ducts in multifamily/residential sections.
  • Reference Residential Appendix RA3.1 — field verification and diagnostic testing procedures for duct leakage (used where the Code requires leakage confirmation).
  • California Mechanical Code Appendix E (Table E 503.7.2) — alternative/expanded minimum duct R‑values by duct location and service type (useful when mechanical requirements apply).

Code references

Grounded in the retrieved California Energy Code — click a citation to read the verbatim passage:

  • § 110.8. High relevance — show source text

    (c) All duct insulation product R -values shall be based on insulation only (excluding air films, vapor retarders or other duct components) and tested C -values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    (d) The installed thickness of duct insulation used to determine its R -value shall be determined as follows:

    1. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used.

    2. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness.

    3. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two.

    (e) Insulated flexible duct products installed to meet this requirement must include labels, in maximum intervals of 3 feet, showing the thermal performance R -value for the duct insulation itself (excluding air films, vapor retarder or other duct components), based on the tests in Section 120.4(c) and the installed thickness determined by Section 120.4(d)3.

    (f) Protection of insulation. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance and wind, but not limited to the following:

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    NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS

    Insulation exposed to weather shall be suitable for outdoor service, e.g., protected by aluminum, sheet metal, painted canvas or plastic cover. Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material.

    (g) Duct sealing. Duct systems shall comply with Subsection 1 or 2 below:

    1. New duct systems that meet the criteria in Subsections A, B, C and D below shall be sealed to a leakage rate not to exceed 6 percent of the nominal air handler airflow rate as confirmed through acceptance testing, in accordance with Reference Nonresidential Appendix NA7.5.3; A. The duct system does not serve a healthcare facility; and B. The duct system provides conditioned air to an occupiable space for a constant volume, single zone, space-conditioning system; and C. The space-conditioning system serves less than 5,000 square feet of conditioned floor area; and D. The combined surface area of the ducts located outdoors or in unconditioned space is more than 25 percent of the total surface area of the entire duct system.
    2. New duct systems that are not subject to testing under Section 120.4(g)1 shall instead meet the duct leakage testing requirements of CMC Section 603.9.2.

    Note: Authority: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code. Reference: Sections 25007, 25008, 25218.5, 25310, 25402, 25402.1, 25402.4, 25402.8, and 25943, Public Resources Code.

    SECTION 120.5—REQUIRED NONRESIDENTIAL MECHANICAL SYSTEM ACCEPTANCE

  • § 110.8. High relevance — show source text

    F. Aerosol-sealant closures.

    i. Aerosol sealants shall meet the requirements of UL 723, and be applied according to manufacturer specifications. ii. Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section. 4. Duct insulation R -value ratings. All duct insulation product R -values shall be based on insulation only (excluding air films, vapor retarder or other duct components) and tested C -values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    1. Duct insulation thickness. The installed thickness of duct insulation used to determine its R -value shall be determined as

    follows:

    A. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used.

    B. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness. C. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. 6. Duct labeling. Insulated flexible duct products installed to meet this requirement shall include labels, in maximum intervals of 3 feet, showing the thermal performance R -value for the duct insulation itself (excluding air films, vapor retarders or other duct components), based on the tests in Section 150.0(m)4 and the installed thickness determined by Section 150.0(m)5C. 7. Backdraft dampers. All fan systems, regardless of volumetric capacity, that exchange air between the building conditioned space and the outside of the building shall be provided with backdraft or automatic dampers to prevent unintended air leakage through the fan system when the fan system is not operating. 8. Gravity ventilation dampers. All gravity ventilating systems that serve conditioned space shall be provided with either automatic or readily accessible, manually operated dampers in all openings to the outside except combustion inlet and outlet air openings and elevator shaft vents. 9. Protection of insulation. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance and wind, but not limited to the following: Insulation exposed to weather shall be suitable for outdoor service, e.g., protected by aluminum, sheet metal, painted canvas or plastic cover. Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material.

    1. Porous inner core flex duct. Flexible ducts having porous inner cores shall have a non-porous layer or air barrier between the inner core and the outer vapor barrier.
    2. Duct system sealing and leakage testing. When space-conditioning systems utilize forced air duct systems to supply conditioned air to an occupiable space, the ducts shall be sealed as confirmed through field verification and diagnostic testing in accordance with all applicable procedures specified in Reference Residential Appendix RA3.1, and conforming to one of the following Subsections A, B or C as applicable. Air handler airflow for calculation of duct leakage rate compliance targets shall be determined according to methods specified in Reference Residential Appendix RA3.1.4.2.
  • § 110.8. High relevance — show source text

    ** A. Factory-made rigid fiberglass and flexible ducts for field-fabricated duct systems shall comply with UL 181. All pressure-sensitive tapes, mastics, aerosol sealants or other closure systems used for installing field-fabricated duct systems shall meet the applicable requirements of UL 181, UL 181A and UL 181B.

    B. Mastic sealants and mesh.

    i. Sealants shall comply with the applicable requirements of UL 181, UL 181A and UL 18IB, and be nontoxic and water resistant.

    ii. Sealants for interior applications shall be tested in accordance with ASTM C731 and D2202 incorporated herein by reference. iii. Sealants for exterior applications shall be tested in accordance with ASTM C731, C732 and D2202, incorporated herein by reference.

    iv. Sealants and meshes shall be rated for exterior use.

    C. Pressure-sensitive tape. Pressure-sensitive tapes shall comply with the applicable requirements of UL 181, UL 181A and UL 181B.

    D. Joints and seams of duct systems and their components shall not be sealed with cloth-back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

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    SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

    E. Drawbands used with flexible duct.

    i. Drawbands shall be either stainless-steel worm- drive hose clamps or UV-resistant nylon duct ties. ii. Drawbands shall have a minimum tensile strength rating of 150 pounds. iii. Drawbands shall be tightened as recommended by the manufacturer with an adjustable tensioning tool.

    F. Aerosol-sealant closures.

    i. Aerosol sealants shall meet the requirements of UL 723, and be applied according to manufacturer specifications. ii. Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section. 4. Duct insulation R -value ratings. All duct insulation product R -values shall be based on insulation only (excluding air films, vapor retarder or other duct components) and tested C -values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    1. Duct insulation thickness. The installed thickness of duct insulation used to determine its R -value shall be determined as

    follows:

    A. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used.

    B. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness. C. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. 6. Duct labeling. Insulated flexible duct products installed to meet this requirement shall include labels, in maximum intervals of 3 feet, showing the thermal performance R -value for the duct insulation itself (excluding air films, vapor retarders or other duct components), based on the tests in Section 150.0(m)4 and the installed thickness determined by Section 150.0(m)5C. 7. **Backdraft dampers.

  • § 160.3 High relevance — show source text

    ii. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness.

    iii. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. F. Duct labeling. Insulated flexible duct products installed to meet this requirement shall include labels, in maximum intervals of 3 feet, showing the thermal performance R- value for the duct insulation itself (excluding air films, vapor retarder or other duct components), based on the tests in Section 160.3(b)5D and the installed thickness determined by Section 160.3(b)5Eiii. G. Backdraft dampers. All fan systems, regardless of volumetric capacity, that exchange air between the building conditioned space and the outside of the building shall be provided with backdraft or automatic dampers to prevent unintended air leakage through the fan system when the fan system is not operating. H. Gravity ventilation dampers. All gravity ventilating systems that serve conditioned space shall be provided with either automatic or readily accessible, manually operated dampers in all openings to the outside except combustion inlet and outlet air openings and elevator shaft vents. I. Protection of insulation. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance and wind but not limited to the following: Insulation exposed to weather shall be suitable for outdoor service (e.g., protected by aluminum, sheet metal, painted canvas or plastic cover). Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material. J. Porous inner core flex duct. Flexible ducts having porous inner cores shall have a nonporous layer or air barrier between the inner core and the outer vapor barrier. K. Duct system sealing and leakage testing. When space-conditioning systems utilize forced air duct systems to supply conditioned air to an individual dwelling unit, the ducts shall be sealed, as confirmed through field verification and diagnostic testing, in accordance with all applicable procedures specified in Reference Residential Appendix RA3.1. Air handler airflow for calculation of duct leakage rate compliance targets shall be determined according to methods specified in Reference Residential Appendix RA3.1.4.2. For multifamily dwellings with the air-handling unit installed and the ducts connected directly to the air handler, regardless of duct system location: i. The total leakage of the duct system shall not exceed 12 percent of the air handler airflow as determined utilizing the procedures in Reference Residential Appendix Section RA3.1.4.3.1; or ii. The duct system leakage to outside shall not exceed 6 percent of the air handler airflow as determined utilizing the procedures in Reference Residential Appendix Section RA3.1.4.3.4.

    • Exception 1 to Section 160.3(b)5K: The field verification and ECC-Provider data registry requirements of Reference Residential Appendix RA2 and RA3 are not required for multifamily dwelling units in buildings four

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    MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

    habitable stories and greater. The installer shall certify that diagnostic testing was performed in accordance with the applicable procedures. Exception 2 to Section 160.3(b)5K: Multifamily dwelling units in buildings four habitable stories and greater in Climate Zones 1, 3, 5 and 7. L.

  • § 110.8. High relevance — show source text

    I. Drawbands shall be either stainless-steel worm-drive hose clamps or UV-resistant nylon duct ties. II. Drawbands shall have a minimum tensile strength rating of 150 pounds. III. Drawbands shall be tightened as recommended by the manufacturer with an adjustable tensioning tool.

    f. Aerosol-sealant closures.

    I. Aerosol sealants shall meet the requirements of UL 723 and be applied according to manufacturer specifications. II. Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section.

    D. All duct insulation product R- values shall be based on insulation only (excluding air films, vapor retarders or other duct components) and tested C-values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    E. The installed thickness of duct insulation used to determine its R- value shall be determined as follows:

    i. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used.

    ii. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness.

    iii. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. F. Insulated flexible duct products installed to meet this requirement must include labels, in maximum intervals of 3 feet, showing the thermal performance R- value for the duct insulation itself (excluding air films, vapor retarder or other duct components), based on the tests in Section 160.3(c)2D and the installed thickness determined by Section 160.3(c)2Eiii. G. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance and wind but not limited to the following: Insulation exposed to weather shall be suitable for outdoor service; e.g., protected by aluminum, sheet metal, painted canvas or plastic cover. Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material. H. Duct systems shall be tested in accordance with i or ii below: i. New duct systems that meet the criteria in Subsections a, b and c below or ductwork that is part of a system that meets the criteria of Section 180.2(b)2B shall be sealed to a leakage rate not to exceed 6 percent of the nominal air handler airflow rate as confirmed through acceptance testing, in accordance with Reference Nonresidential Appendix NA7.5.3. a. The duct system provides conditioned air to an occupiable space for a constant volume, single zone, space-conditioning system; and b. The space-conditioning system serves less than 5,000 square feet of conditioned floor area; and c. The combined surface area of the ducts located in the following spaces is more than 25 percent of the total surface area of the entire duct system:

    I. Outdoors; or

    II. In a space directly under a roof that has a U- factor greater than the U- factor of the ceiling, or if the roof does not meet the requirements of Section 170.2(a)1; or III. In a space directly under a roof that has fixed vents or openings to the outside or unconditioned

  • § 110.8. High relevance — show source text

    c. Sealants for exterior applications shall be tested in accordance with ASTM C731, C732 and D2202, incorporated herein by reference.

    d. Sealants and meshes shall be rated for exterior use.

    iii. Pressure-sensitive tape. Pressure-sensitive tapes shall comply with the applicable requirements of UL 181, UL 181A and UL 181B.

    iv. Joints and seams of duct systems and their components shall not be sealed with cloth back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

    v. Drawbands used with flexible duct.

    a. Drawbands shall be either stainless-steel worm-drive hose clamps or UV-resistant nylon duct ties. b. Drawbands shall have a minimum tensile strength rating of 150 pounds. c. Drawbands shall be tightened as recommended by the manufacturer with an adjustable tensioning tool.

    vi. Aerosol-sealant closures.

    a. Aerosol sealants shall meet the requirements of UL 723 and be applied according to manufacturer specifications. b. Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section. D. Duct insulation R- value ratings. All duct insulation product R- values shall be based on insulation only (excluding air films, vapor retarder or other duct components) and tested C-values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    E. Duct insulation thickness. The installed thickness of duct insulation used to determine its R- value shall be deter mined as follows:

    i. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used .

    ii. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness.

    iii. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. F. Duct labeling. Insulated flexible duct products installed to meet this requirement shall include labels, in maximum intervals of 3 feet, showing the thermal performance R- value for the duct insulation itself (excluding air films, vapor retarder or other duct components), based on the tests in Section 160.3(b)5D and the installed thickness determined by Section 160.3(b)5Eiii. G. Backdraft dampers. All fan systems, regardless of volumetric capacity, that exchange air between the building conditioned space and the outside of the building shall be provided with backdraft or automatic dampers to prevent unintended air leakage through the fan system when the fan system is not operating. H. Gravity ventilation dampers. All gravity ventilating systems that serve conditioned space shall be provided with either automatic or readily accessible, manually operated dampers in all openings to the outside except combustion inlet and outlet air openings and elevator shaft vents. I. Protection of insulation. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance and wind but not limited to the following: Insulation exposed to weather shall be suitable for outdoor service (e.g., protected by aluminum, sheet metal, painted canvas or plastic cover). Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material. J. **Porous inner core flex duct.

  • § 4.15 High relevance — show source text

    91|AHRI 1250|July 10, 2020| |Unit cooler, low temperature,
    net capacity (qnet) ≥ 15 500 Btu/h|UC.L,
    ≥15 500 Btu/h|4.15|AHRI 1250|July 10, 2020|

    For SI units: 1000 British thermal units per hour = 0.293 kW

    • qnet is net capacity (Btu/h) as determined in accordance with AHRI 1250.

    2025 CALIFORNIA MECHANICAL CODE 473

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    APPENDIX E

    Col1 TABLE E 503.7.2 MINIMUM DUCT INSULATION R-VALUE1 [ASHRAE 90.1: TABLE 6.8.2] Col3 Col4
    CLIMATE ZONE DUCT LOCATION DUCT LOCATION DUCT LOCATION
    CLIMATE ZONE EXTERIOR2 UNCONDITIONED SPACE AND
    BURIED DUCTS    		 INDIRECTLY CONDITIONED
    SPACE3, 4
    SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING SUPPLY AND RETURN DUCTS FOR HEATING AND COOLING
    0 to 4 R-8 R-6 R-1.9
    5 to 8 R-12 R-6 R-1.9
    SUPPLY AND RETURN DUCTS FOR HEATING ONLY SUPPLY AND RETURN DUCTS FOR HEATING ONLY SUPPLY AND RETURN DUCTS FOR HEATING ONLY SUPPLY AND RETURN DUCTS FOR HEATING ONLY
    0 to 1 none none none
    2 to 4 R-6 R-6 R-1.9
    5 to 8 R-12 R-6 R-1.9
    SUPPLY AND RETURN DUCTS FOR COOLING ONLY SUPPLY AND RETURN DUCTS FOR COOLING ONLY SUPPLY AND RETURN DUCTS FOR COOLING ONLY SUPPLY AND RETURN DUCTS FOR COOLING ONLY
    0 to 6 R-8 R-6 R-1.9
    7 to 8 R-1.9 R-1.9 R-1.9

    Notes: 1 Insulation R-values, measured in [°F•h•ft 2 /(Btu•in)] [(m•K)/W], are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where portions of the building envelope are used as a plenum enclosure, building envelope insulation shall be as required by the most restrictive condition of Section E 503.4.7.1 or ASHRAE 90.1, depending on whether the plenum is located in the roof, wall, or floor. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75°F (24°C) at the installed thickness. 2 Includes attics above insulated ceilings, parking garages and crawl spaces. 3 Includes return air plenums, with or without exposed roofs above.

  • § 1.9 High relevance — show source text

    9| |7 to 8|R-1.9|R-1.9|R-1.9|

    Notes: 1 Insulation R-values, measured in [°F•h•ft 2 /(Btu•in)] [(m•K)/W], are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where portions of the building envelope are used as a plenum enclosure, building envelope insulation shall be as required by the most restrictive condition of Section E 503.4.7.1 or ASHRAE 90.1, depending on whether the plenum is located in the roof, wall, or floor. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75°F (24°C) at the installed thickness. 2 Includes attics above insulated ceilings, parking garages and crawl spaces. 3 Includes return air plenums, with or without exposed roofs above. 4 Return ducts in this duct location do not require insulation.

    TABLE E 503.7.3(1) MINIMUM PIPE INSULATION THICKNESS FOR HEATING AND HOT WATER SYSTEMS [1, 2, 3, 4, 5]

    (STEAM, STEAM CONDENSATE, HOT WATER HEATING, AND DOMESTIC WATER SYSTEMS)

    [ASHRAE 90.1: TABLE 6.8.3-1]

    FLUID OPERATING
    TEMPERATURE RANGE
    (F°) AND USAGE    		 INSULATION CONDUCTIVITY Col3 NOMINAL PIPE SIZE OR TUBE SIZE (inches) Col5 Col6 Col7 Col8
    FLUID OPERATING
    TEMPERATURE RANGE
    (F°) AND USAGE    		 CONDUCTIVITY
    Btu•inch/(h•ft2•°F)    		 MEAN RATING
    TEMPERATURE
    °F    		 <1 1 to <11_/_2 11_/_2 to <4 4 to <8 ≥8
    FLUID OPERATING
    TEMPERATURE RANGE
    (F°) AND USAGE    		 CONDUCTIVITY
    Btu•inch/(h•ft2•°F)    		 MEAN RATING
    TEMPERATURE
    °F    		 INSULATION THICKNESS (inches) INSULATION THICKNESS (inches) INSULATION THICKNESS (inches) INSULATION THICKNESS (inches) INSULATION THICKNESS (inches)
    >350 0.32 to 0.34 250 4.5 5.0 5.0 5.0 5.0
    251 to 350 0.29 to 0.32 200 3.0 4.0 4.5 4.5 4.5
    201 to 250 0.27 to 0.30 150 2.5 2.5 2.5 3.0 3.0
    141 to 200 0.25 to 0.29 125 1.5 1.5 2.0 2.0 2.0
    105 to 140 0.22 to 0.28 100 1.
  • § 2.5 High relevance — show source text

    b**| |4|Vented cladding over wood structural panels
    Vented cladding over fiberboard
    Vented cladding over gypsum
    Continuous insulation with_R_-value ≥ R-2.5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-3.75 over 2 × 6 wall| |5|Vented cladding over wood structural panels
    Vented cladding over fiberboard
    Vented cladding over gypsum
    Continuous insulation with_R_-value ≥ R-5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-7.5 over 2 × 6 wall| |6|Vented cladding over fiberboard
    Vented cladding over gypsum
    Continuous insulation with_R_-value ≥ R-7.5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-11.25 over 2 × 6 wall| |7|Continuous insulation with_R_-value ≥ R-10 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-15 over 2 × 6 wall| |8|Continuous insulation with_R_-value ≥ R-12.5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-20 over 2 × 6 wall| |a. Vented cladding shall include vinyl lap siding, polypropylene, horizontal aluminum siding, brick veneer with airspace as specified in this code, rainscreen systems and other
    approved vented claddings.
    b. The requirements in this table apply only to insulation used to control moisture in order to permit the use of Class III vapor retarders. The insulation materials used to satisfy
    this option also contribute to but do not supersede the building thermal envelope requirements of the_California Energy Code_.|a. Vented cladding shall include vinyl lap siding, polypropylene, horizontal aluminum siding, brick veneer with airspace as specified in this code, rainscreen systems and other
    approved vented claddings.
    b. The requirements in this table apply only to insulation used to control moisture in order to permit the use of Class III vapor retarders. The insulation materials used to satisfy
    this option also contribute to but do not supersede the building thermal envelope requirements of the_California Energy Code_.|

    2025 CALIFORNIA BUILDING CODE 14-7

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    TABLE 1404.3(4)—CONTINUOUS INSULATION WITH A CLASS I OR II RESPONSIVE VAPOR RETARDER Col2
    CLIMATE ZONE PERMITTED CONDITIONSa
    3 Continuous insulation with_R_-value ≥ R-2
    4, 5, 6 Continuous insulation with_R_-value ≥ R-3 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-5 over 2 × 6 wall
    7 Continuous insulation with_R_-value ≥ R-5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-7.5 over 2 × 6 wall
    8 Continuous insulation with_R_-value ≥ R-7.5 over 2 × 4 wall
    Continuous insulation with_R_-value ≥ R-10 over 2 × 6 wall
    a. The requirements in this table apply only to insulation used to control moisture in order to permit the use of Class I or II vapor retarders.
  • § 203.1.2 High relevance — show source text

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    APPENDIX A4 — RESIDENTIAL VOLUNTARY MEASURES

    A4.203.1.2 Prerequisite options. In addition, a minimum of TWO of the efficiency measures specified in Sections A4.203.1.2.1 through A4.203.1.2.7 must be met.

    A4.203.1.2.1 Roof deck insulation, or ducts in conditioned space. Meet one of the three options for the location of ducts and air handlers as well as insulation R -values and installation of a radiant barrier as specified in Title 24, Part 6, Section 150.1(c)9A or B:

    1. Below roof deck insulation with a minimum R -value of 19; or,

    2. Continuous above deck insulation with a minimum R-8 and with an air space present between the roofing and the roof deck; or,

    3. All ducts and air handlers in conditioned space as specified in the Title 24, Part 6, Reference Appendix RA3.1.

    A4.203.1.2.2 High performance walls. Meet the climate zone dependent U -factor or insulation R -value for either 2x6 or 2x4 framing as specified in Title 24, Part 6, Section 150.1(c)1B: maximum U -factor of 0.048.

    A4.203.1.2.3 Compact hot water distribution system. Meet the requirements for installation of Compact Hot Water Distribution Systems specified in the Title 24, Part 6, Reference Appendix RA3.6.5.

    A4.203.1.2.4 Drain water heat recovery. Meet the requirements for installation of Drain Water Heat Recovery specified in Title 24, Part 6, Reference Appendix RA4.4.21.

    A4.203.1.2.5 High performance vertical fenestration. Meet the climate zone dependent U -factor and Solar Heat Gain Coefficient (SHGC) as rated in accordance with Title 24, Part 6, Section 110.6, and shall have a maximum U -factor of 0.21 in Climate Zones 1 − 16, maximum SHGC of 0.23 in Climate Zones 2, 4, and 6 − 14, and maximum SHGC of 0.20 in Climate Zone 15.

    Exception to A4.203.1.2.5: Fenestration in Climate Zones 1, 3, 5, and 16 is not required to comply with the maximum SHGC requirements.

    A4.203.1.2.6 Heat pump water heater demand management. For buildings with heat pump water heating, meet the requirements for installation of controls specified by Title 24, Part 6, Reference Appendix JA13.3.3.

    A4.203.1.2.7 Battery storage system controls. For buildings with battery storage systems, meet the requirements for installation of controls specified by Title 24, Part 6, Reference Appendix JA12 for either the Time-of-Use Control or Advanced Demand Flexibility Control option.

  • § 160.3 High relevance — show source text

    Exception to Section 160.3(c)2Cid: Ductwork located in occupied space and exposed to view. ii. Field-fabricated duct systems. a. Factory-made rigid fiberglass and flexible ducts for field-fabricated duct systems shall comply with UL 181. All pressure-sensitive tapes, mastics, aerosol sealants or other closure systems used for installing field-fabricated duct systems shall meet the applicable requirements of UL 181, UL 181A and UL 181B.

    b. Mastic sealants and mesh.

    I. Sealants shall comply with the applicable requirements of UL 181, UL 181A and UL 181B, and be nontoxic and water resistant.

    II. Sealants for interior applications shall pass ASTM C731 (extrudability after aging) and D2202 (slump test on vertical surfaces), incorporated herein by reference. III. Sealants for exterior applications shall pass ASTM C731, C732 (artificial weathering test) and D2202, incorporated herein by reference.

    IV. Sealants and meshes shall be rated for exterior use.

    2025 CALIFORNIA ENERGY CODE 219

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

    c. Pressure-sensitive tape. Pressure-sensitive tapes shall comply with the applicable requirements of UL 181, UL 181A and UL 181B.

    d. Ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.

    e. Drawbands used with flexible duct.

    I. Drawbands shall be either stainless-steel worm-drive hose clamps or UV-resistant nylon duct ties. II. Drawbands shall have a minimum tensile strength rating of 150 pounds. III. Drawbands shall be tightened as recommended by the manufacturer with an adjustable tensioning tool.

    f. Aerosol-sealant closures.

    I. Aerosol sealants shall meet the requirements of UL 723 and be applied according to manufacturer specifications. II. Tapes or mastics used in combination with aerosol sealing shall meet the requirements of this section.

    D. All duct insulation product R- values shall be based on insulation only (excluding air films, vapor retarders or other duct components) and tested C-values at 75°F mean temperature at the installed thickness, in accordance with ASTM C518 or ASTM C177, incorporated herein by reference, and certified pursuant to Section 110.8.

    E. The installed thickness of duct insulation used to determine its R- value shall be determined as follows:

    i. For duct board, duct liner and factory-made rigid ducts not normally subjected to compression, the nominal insulation thickness shall be used.

    ii. For duct wrap, installed thickness shall be assumed to be 75 percent (25 percent compression) of nominal thickness.

    iii. For factory-made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. F. Insulated flexible duct products installed to meet this requirement must include labels, in maximum intervals of 3 feet, showing the thermal performance R- value for the duct insulation itself (excluding air films, vapor retarder or other duct components), based on the tests in Section 160.3(c)2D and the installed thickness determined by Section 160.3(c)2Eiii.

  • § 203.1.1 High relevance — show source text

    A4.203.1.1 Long-term system cost (LSC). LSC rating for the building’s Proposed Design shall be computed by Compliance Software certified by the Energy Commission as specified in Title 24, Part 6, Section 100.1 and 150.1(b), and shall reduce the LSC required in the Compliance Software for minimum performance-based compliance with the California Energy Code by the compliance margin specified in Table A4.203.1.1. The rating shall be included in the Certificate of Compliance documentation.

    TABLE A4.203.1.1—RECOMMENDED LSC MARGINS BY CLIMATE ZONES Col2
    CALIFORNIA ENERGY CODE CLIMATE ZONE TOTAL LSC COMPLIANCE MARGIN
    1 2.70
    2 1.62
    3 1.10
    4 1.11
    5 1.01
    6 0.24
    7 0.24
    8 0.21
    9 0.20
    10 0.18
    11 1.11
    12 1.05
    13 0.96
    14 1.21
    15 0.59
    16 1.68
    Note: Community shared options complying with Title 24, Part 1, Section 10-115 may be used to achieve LSC targets. Note: Community shared options complying with Title 24, Part 1, Section 10-115 may be used to achieve LSC targets.

    2025 CALIFORNIA GREEN BUILDING STANDARDS CODE APPENDIX A4-9

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    APPENDIX A4 — RESIDENTIAL VOLUNTARY MEASURES

    A4.203.1.2 Prerequisite options. In addition, a minimum of TWO of the efficiency measures specified in Sections A4.203.1.2.1 through A4.203.1.2.7 must be met.

    A4.203.1.2.1 Roof deck insulation, or ducts in conditioned space. Meet one of the three options for the location of ducts and air handlers as well as insulation R -values and installation of a radiant barrier as specified in Title 24, Part 6, Section 150.1(c)9A or B:

    1. Below roof deck insulation with a minimum R -value of 19; or,

    2. Continuous above deck insulation with a minimum R-8 and with an air space present between the roofing and the roof deck; or,

    3. All ducts and air handlers in conditioned space as specified in the Title 24, Part 6, Reference Appendix RA3.1.

    A4.203.1.2.2 High performance walls. Meet the climate zone dependent U -factor or insulation R -value for either 2x6 or 2x4 framing as specified in Title 24, Part 6, Section 150.1(c)1B: maximum U -factor of 0.048.

    A4.203.1.2.3 Compact hot water distribution system. Meet the requirements for installation of Compact Hot Water Distribution Systems specified in the Title 24, Part 6, Reference Appendix RA3.6.5.

Frequently asked questions

Do the R‑values in Table 150.2‑D apply to both supply and return ducts?

Yes — Table 150.2‑D establishes the minimum duct R‑value for ducts in unconditioned space by climate zone. For more nuanced supply vs return or duct‑location differences consult the Mechanical Code Appendix tables where applicable.

How often must flexible ducts be labeled and what must the label show?

Flexible ducts must include labels at maximum 3‑foot intervals showing the thermal performance R‑value of the insulation only, based on ASTM testing at the installed thickness. See § 160.3(b)5D/E.

If my duct wrap is specified as 1‑inch nominal, what installed thickness do I use to find the R?

For duct wrap, assume 75% of nominal thickness (i.e., 1.0 in nominal → 0.75 in installed) when using the manufacturer’s tested R at installed thickness.

Can I count a foil facer or vapor retarder toward the Code R‑value?

No. The Code requires the R‑value of the insulation only (exclude air films, facers, vapor retarders and other duct components) and that the R be tested at the installed thickness.

What if my project is in a Climate Zone listed as R‑6 but ducts are outdoors?

Table 150.2‑D is the energy‑code minimum for ducts in unconditioned spaces; if ducts are outdoors or otherwise in a different location category, consult the more specific Mechanical Code tables (which separate exterior, unconditioned, and indirectly conditioned locations).

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