Title 24 · California Energy Code

Vapor retarder installation requirements and spray foam criteria for moisture control

The code lets interior spray foam serve as the moisture control layer if its installed permeance is ≤ 1.5 perms and its installed R (alone or combined with exterior continuous insulation) meets the R required for your climate and framing; vapor retarders must be installed per the manufacturer or approved design and, if they are the air barrier, must meet Energy Code air‑barrier requirements (see **§ 1404.3.1** and **§ 1404.3.2**).

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

The code allows spray foam applied to the interior face of sheathing or gypsum to serve as the moisture-control layer when the foam has a maximum permeance of 1.5 perms at the installed thickness and its installed R‑value meets (or combined with exterior continuous insulation equals or exceeds) the required continuous‑insulation R‑value; this is the spray‑foam compliance pathway in § 1404.3.1. Vapor retarders (Class I, II, III) must be installed per the manufacturer’s instructions or an approved design, and if the vapor retarder also functions as a component of the continuous air barrier it must be installed as an air barrier in accordance with the Energy Code; see § 1404.3.2.

The single most important plain‑English rule: If you use spray foam on the interior face for moisture control, the foam must be ≤ 1.5 perms at installed thickness and its installed R (alone or combined with exterior continuous insulation) must meet the continuous insulation requirement in the applicable table — otherwise you must provide a separate compliant vapor control layer.

Requirements in detail

Key defined terms (first appearance bolded)

  • Vapor retarder — a material or layer classified by permeance into Class I, II, or III as shown in Table 1404.3(1).
  • Permeance — water‑vapor permeance (perm) measured per ASTM E96; used to classify vapor retarder class and limits for spray foam and control layers.
  • Continuous insulation — exterior continuous insulation used for moisture control in certain compliance paths; its required R‑value is given in Tables 1404.3(4) and 1404.3(5).
  • Responsive vapor retarder — referenced in the tables as an allowed option where specifically noted; see Tables 1404.3(2) and 1404.3(4).

Spray foam criteria for moisture control — what the code says (controlled by § 1404.3.1)

  • Spray foam applied to the interior side of wood structural panels, fiberboard, insulating sheathing or gypsum may be treated as the continuous insulation moisture‑control layer if:

    • the spray foam has a maximum permeance of 1.5 perms at the installed thickness, and
    • one of these two conditions is met:
      1. the installed R‑value of the spray foam alone meets or exceeds the specified continuous insulation R‑value; or
      2. the combined R‑value of the spray foam plus the exterior continuous insulation equals or exceeds the specified continuous insulation R‑value.

  • These spray‑foam criteria are specifically for compliance with the continuous‑insulation moisture‑control requirements referenced in Tables 1404.3(3) and 1404.3(4).

Vapor retarder installation — what the code requires (controlled by § 1404.3.2)

  • Vapor retarders shall be installed in accordance with the manufacturer’s instructions or an approved design. If the vapor retarder also serves as a component of the continuous air barrier, it must be installed as an air barrier in accordance with the California Energy Code. This is the entirety of the installation requirement in § 1404.3.2.

Decision‑relevant dimensions & values (quick reference table)

Decision factor Required value / classification When it applies Code Reference
Spray foam maximum permeance (installed thickness) 1.5 perms To treat interior‑applied spray foam as the moisture‑control layer § 1404.3.1
Vapor retarder classes Class I ≤ 0.1 perm, Class II >0.1 – ≤1.0 perm, Class III >1.0 – ≤10.0 perm For selecting interior vapor retarder materials § 1404.3 / Table 1404.3(1)
External water‑vapor control layer permeance when omitting interior retarder ≤ 1 perm (ASTM E96, Procedure A, dry cup) Required on exterior side when assembly relies on exterior water‑vapor control per Table 1404.3(5) Table 1404.3(5)
Continuous insulation R‑value thresholds Climate‑zone and framing dependent (see table below) Determines required R that spray foam must meet or combine to meet Tables 1404.3(4), 1404.3(5) § 1404.3.1
Installation standard for vapor retarders Manufacturer’s instructions or approved design; if acting as air barrier, comply with Energy Code air‑barrier requirements All vapor retarder installations § 1404.3.2

Representative continuous‑insulation R‑value triggers (decision table)

Climate zone (reference) Example required continuous insulation (2×4 wall) Code Reference
3 R‑2 Table 1404.3(4)
4–6 R‑3 (2×4 walls) Table 1404.3(4)
7 R‑5 (2×4 walls) Table 1404.3(4)
8 R‑7.5 (2×4 walls) Table 1404.3(4)

(Use the full Table 1404.3(4) values for exact conditions; these examples show the decision thresholds that determine whether the spray foam R alone or the spray‑foam + continuous‑insulation combination meets the code pathway.)

Exceptions & special cases

  • A vapor retarder is not required in Climate Zones 1, 2, and 3 (see § 1404.3 exceptions).
  • Exceptions in § 1404.3 also exclude basement walls and below‑grade portions of walls from the vapor‑retarder requirement.
  • Where the assembly complies with Table 1404.3(5) (continuous insulation on walls without an interior vapor retarder), an exterior water vapor control material with permeance ≤ 1 perm (ASTM E96, Procedure A) is required on the exterior side of the wall and to the interior side of the exterior continuous insulation — the exterior CI can serve as the vapor control where it qualifies as Class I or II.
  • If a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing on the exterior, that continuous insulation must comply with Table 1404.3(4) and the interior Class I/II retarder must be a responsive vapor retarder where the table requires it.

If you need an approved design or hygrothermal analysis (for atypical assemblies, two-sided Class I retarders, or when R‑values on one side exceed limits), the code permits using an approved design based on accepted engineering hygrothermal practice.

Common mistakes

  • Misreading the permeance limit: the spray‑foam pathway requires ≤ 1.5 perms at the installed thickness (not the manufacturer’s nominal open‑cell or closed‑cell “type” claim). Confirm permeance at the installed thickness per ASTM E96. § 1404.3.1.
  • Treating a vapor retarder as compliant without following the manufacturer’s installation instructions or an approved design — § 1404.3.2 requires following those instructions; noncontinuous or poorly sealed installations fail the requirement.
  • Forgetting the air‑barrier requirement: if the vapor retarder also is intended to serve as the continuous air barrier, it must be installed to meet the Energy Code air‑barrier requirements — installation as an air barrier is not optional. § 1404.3.2.
  • Applying the spray‑foam 1.5‑perm allowance to interior finishes or materials other than the listed substrates (interior face of wood structural panels, fiberboard, insulating sheathing, or gypsum) without verifying the code pathway applies. § 1404.3.1 limits the listed assemblies.

Worked example — concrete scenario with numbers

Scenario: New 2×4 framed exterior wall in Climate Zone 5 with exterior continuous insulation and interior spray foam applied to gypsum.

  1. Find the required continuous‑insulation R for CZ5, 2×4 wall: Table 1404.3(4) lists R‑3 (2×4) for Climate Zones 4, 5, 6. Use that R target.
  2. Confirm spray foam permeance at installed thickness is ≤ 1.5 perms (ASTM E96 test result for the installed thickness). If the installed spray foam permeance is ≤ 1.5 perms, it may be used under the § 1404.3.1 pathway.
  3. Check R: If the installed spray foam’s installed R‑value is ≥ R‑3 then the spray foam alone meets the continuous insulation moisture‑control requirement and the assembly is compliant per § 1404.3.1. If the spray foam R < R‑3, then determine the combined R of spray foam + exterior continuous insulation; if the combined R ≥ R‑3, the pathway is still met.
  4. Install any vapor retarder per the manufacturer’s instructions or an approved design; if the interior vapor retarder doubles as the air barrier, install it to meet the Energy Code air‑barrier requirements as required by § 1404.3.2.

This example follows the exact compliance pathway in § 1404.3.1 and installation requirement in § 1404.3.2.

Related provisions (sections to review)

  • § 1404.3 — Vapor retarders (classification, general requirements, exceptions)
  • § 1404.3.1 — Spray foam plastic insulation for moisture control with Class II and III vapor retarders (spray‑foam permeance and R‑value pathway)
  • § 1404.3.2 — Vapor retarder installation (manufacturer’s instructions / approved design; air‑barrier requirement)
  • § 1404.3.3 — California Energy Code and IECC climate zones (climate zone mapping used by these sections)
  • Table 1404.3(1) — Vapor retarder materials and classes (Class I/II/III permeance ranges)
  • Table 1404.3(4) — Continuous insulation conditions when a Class I or II responsive vapor retarder is used (R‑value thresholds by climate zone)
  • Table 1404.3(5) — Continuous insulation options in lieu of an interior vapor retarder (exterior water‑vapor control layer permeance and limits)
  • California Energy Code — vapor retarder requirements for crawlspaces and other contexts (see Section 160.1(d) and related crawlspace provisions) for related vapor retarder duties in the Energy Code.

If you want, I can extract the exact lines from Tables 1404.3(4) and 1404.3(5) for your specific climate zone and framing (2×4 vs 2×6) and present a checklist you can hand to installers.

Code references

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

  • § 1404.3.1 High relevance — show source text

    The exterior continuous insulation shall be permitted to serve as the vapor control layer where, at its
    installed thickness or with a facer on its interior face, the exterior continuous insulation is a Class I or II vapor retarder.
    c. The requirements of this table apply only to continuous insulation used to control moisture in order to allow walls without a Class I, II or III interior vapor retarder. The insula-
    tion materials used to satisfy this option also contribute to but do not supersede the_building_ thermal envelope requirements of the_California Energy Code_.|a. The total insulating value of materials to the interior side of the exterior continuous insulation, including any cavity insulation, shall not exceed R-5. Where the_R_-value of
    materials to the interior side of the exterior continuous insulation exceeds R-5, an_approved_ design shall be required.
    b. A water vapor control material layer having a permeance of not greater than 1 perm in accordance with ASTM E96, Procedure A (dry cup) shall be placed on the exterior side
    of the wall and to the interior side of the exterior continuous insulation. The exterior continuous insulation shall be permitted to serve as the vapor control layer where, at its
    installed thickness or with a facer on its interior face, the exterior continuous insulation is a Class I or II vapor retarder.
    c. The requirements of this table apply only to continuous insulation used to control moisture in order to allow walls without a Class I, II or III interior vapor retarder. The insula-
    tion materials used to satisfy this option also contribute to but do not supersede the_building_ thermal envelope requirements of the_California Energy Code_.|

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    EXTERIOR WALLS

    1404.3.1 Spray foam plastic insulation for moisture control with Class II and III vapor retarders. For purposes of compliance with Tables 1404.3(3) and 1404.3(4), spray foam with a maximum permeance of 1.5 perms at the installed thickness applied to the interior side of wood structural panels, fiberboard, insulating sheathing or gypsum shall be deemed to meet the continuous insulation moisture control requirement in accordance with one of the following conditions:

    1. The spray foam R -value meets or exceeds the specified continuous insulation R-value.
    2. The combined R -value of the spray foam and continuous insulation is equal to or greater than the specified continuous insulation R -value.

    1404.3.2 Vapor retarder installation. Vapor retarders shall be installed in accordance with the manufacturer’s instructions or an approved design. Where a vapor retarder also functions as a component of a continuous air barrier, the vapor retarder shall be installed as an air barrier in accordance with the California Energy Code . 1404.3.3 California Energy Code and International Energy Conservation Code Climate Zones. The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Chapter 12, Table 1202.3.1. 1404.4 Flashing. Flashing shall be installed in such a manner so as to prevent moisture from entering the exterior wall or to redirect that moisture to the surface of the exterior wall covering or to a water-resistive barrier complying with Section 1403.2 and that is part of a means of drainage complying with Section 1402.2.

  • § 7.1 High relevance — show source text

    The requirements in this table apply only to insulation used to control moisture in order to allow walls without a Class I, II or III interior vapor retarder. The insulation materi-
    als used to satisfy this option also contribute to but do not supersede the thermal envelope requirements of the_California Energy Code_.|

    R702.7.1 Spray foam plastic insulation for moisture control with Class II and III vapor retarders. For purposes of compliance with Tables R702.7(3) and R702.7(4), spray foam with a maximum permeance of 1.5 perms at the installed thickness applied to the interior side of wood structural panels, fiberboard, insulating sheathing or gypsum shall be deemed to meet the continuous insulation moisture control requirement in accordance with one of the following conditions:

    1. The spray foam R -value is equal to or greater than the specified continuous insulation R -value.
    2. The combined R -value of the spray foam and continuous insulation is equal to or greater than the specified continuous insulation R -value.

    R702.7.2 Vapor retarder installation. Vapor retarders shall be installed in accordance with the manufacturer’s instructions, accepted installation methods or an approved design. Where a vapor retarder also functions as a component of a continuous air barrier, the vapor retarder shall be installed as an air barrier in accordance with Section N1102.5.1.1.

    R702.7.3 California Energy Code and International Energy Conservation Code Climate Zones. The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Table R702.7.3.

    TABLE R702.7.3—IECC VS. CALIFORNIA ENERGY CODE CLIMATE ZONE COMPARISON Col2 Col3
    IECCa CALIFORNIA
    ENERGY CODE    		 DESCRIPTIONb
    _6 _ 16 Includes Alpine, Mono Counties
    _5 _ 11, 12, 16 Includes Siskiyou, Modoc, Lassen, Plumas, Sierra, Nevada Counties
    4 (marine) 1, 2, 16 Includes Del Norte and Humboldt Counties
    _4 _ 2, 12, 13, 16 Includes Inyo, Trinity, Lake, El Dorado, Amador, Calaveras, Tuolumne, Mariposa Counties
    _3 _ 8, 9, 10,11,12,
    13, 14, 15, 16    		 Includes Shasta, Tehama, Butte, Glenn, Colusa, Yuba, Contra Costa, Sutter, Yolo, Sacramento, Placer, San Joaquin,
    Solano, Stanislaus, Merced, Madera, Fresno, Kings, Tulare, Kern, Ventura, Los Angeles, Orange, San Bernardino, River-
    side Counties
    3 (marine) 1, 2, 3, 4, 5, 6,
    9, 12, 16    		 Includes Mendocino, Sonoma, Marin, San Francisco, San Mateo, Alameda, Santa Cruz, Monterey, San Benito,
    San Luis Obispo, Santa Barbara, Ventura, San Diego Counties
    _2 _ _14,
  • § 1404.3.1 High relevance — show source text

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    EXTERIOR WALLS

    1404.3.1 Spray foam plastic insulation for moisture control with Class II and III vapor retarders. For purposes of compliance with Tables 1404.3(3) and 1404.3(4), spray foam with a maximum permeance of 1.5 perms at the installed thickness applied to the interior side of wood structural panels, fiberboard, insulating sheathing or gypsum shall be deemed to meet the continuous insulation moisture control requirement in accordance with one of the following conditions:

    1. The spray foam R -value meets or exceeds the specified continuous insulation R-value.
    2. The combined R -value of the spray foam and continuous insulation is equal to or greater than the specified continuous insulation R -value.

    1404.3.2 Vapor retarder installation. Vapor retarders shall be installed in accordance with the manufacturer’s instructions or an approved design. Where a vapor retarder also functions as a component of a continuous air barrier, the vapor retarder shall be installed as an air barrier in accordance with the California Energy Code . 1404.3.3 California Energy Code and International Energy Conservation Code Climate Zones. The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Chapter 12, Table 1202.3.1. 1404.4 Flashing. Flashing shall be installed in such a manner so as to prevent moisture from entering the exterior wall or to redirect that moisture to the surface of the exterior wall covering or to a water-resistive barrier complying with Section 1403.2 and that is part of a means of drainage complying with Section 1402.2. Flashing shall be installed at the perimeters of exterior door and window assemblies in accordance with Section 1404.4.1, penetrations and terminations of exterior wall assemblies, exterior wall intersections with roofs, chimneys, porches, decks, balconies and similar projections and at built-in gutters and similar locations where moisture could enter the wall. Flashing with projecting flanges shall be installed on both sides and the ends of copings, under sills and continuously above projecting trim. Where self-adhered membranes are used as flashings of fenestration in exterior wall assemblies, those self-adhered flashings shall comply with AAMA 711. Where fluid applied membranes are used as flashing for exterior wall openings, those fluid applied membrane flashings shall comply with AAMA 714. 1404.4.1 Fenestration flashing. Flashing of the fenestration to the wall assembly shall comply with the fenestration manufacturer’s instructions or, for conditions not addressed by the fenestration manufacturer’s instructions, shall comply with one of the following:

    1. The water-resistive barrier manufacturer’s flashing instructions.
    2. The flashing manufacturer’s flashing instructions.
    3. A flashing design or method of a registered design professional.
    4. Other approved methods. 1404.4.2 Exterior wall pockets. In exterior walls of buildings or structures, wall pockets or crevices in which moisture can accumulate shall be avoided or protected with caps or drips, or other approved means shall be provided to prevent water damage.
  • § 1404.3 High relevance — show source text

    Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.|a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.|a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.|

    TABLE 1404.3(3)—CLASS III VAPOR RETARDERS Col2
    ZONE CLASS III VAPOR RETARDERS PERMITTED FOR:a, 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.
  • § 0.5 High relevance — show source text

    Wood siding of thicknesses less than 0.5 inch shall be placed over sheathing that conforms to Section 2304.6.
    b. Exclusive of texture.
    c. As measured at the bottom of decorative grooves.
    d. 16 ounces per square foot for cold-rolled copper and lead-coated copper, 12 ounces per square foot for copper shingles, high-yield copper and lead-coated high-yield copper.|

    14-6 2025 CALIFORNIA BUILDING CODE

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

    EXTERIOR WALLS

    1404.3 Vapor retarders. Vapor retarder materials shall be classified in accordance with Table 1404.3(1). A vapor retarder shall be provided on the interior side of frame walls in accordance with Table 1404.3(2) and Tables 1404.3(3) or 1404.3(4) as applicable, or an approved design using accepted engineering practice for hygrothermal analysis. Vapor retarders shall be installed in accordance with Section 1404.3.2. The appropriate climate zone shall be selected in accordance with the California Energy Code .

    Exceptions:

    1. Basement walls.

    2. Below-grade portion of any wall.

    3. Construction where accumulation, condensation or freezing of moisture will not damage the materials.

    4. A vapor retarder shall not be required in Climate Zones 1, 2, and 3.

    5. In Climate Zones 4 through 8, a vapor retarder on the interior side of frame walls shall not be required where the assembly complies with Table 1404.3(5).

    TABLE 1404.3(1)—VAPOR RETARDER MATERIALS AND CLASSES Col2
    VAPOR RETARDER CLASS ACCEPTABLE MATERIALS
    I Sheet polyethylene, nonperforated aluminum foil, or other approved materials with a perm rating of less than or
    equal to 0.1
    II Kraft-faced fiberglass batts or vapor retarder paint or other approved materials, applied in accordance with the
    manufacturer’s instructions for a perm rating greater than 0.1 and less than or equal to 1.0
    III Latex paint, enamel paint, or other approved materials, applied in accordance with the manufacturer’s instruc-
    tions for a perm rating of greater than 1.0 and less than or equal to 10
    TABLE 1404.3(2)—VAPOR RETARDER OPTIONS Col2 Col3 Col4
    CLIMATE ZONE VAPOR RETARDER CLASS VAPOR RETARDER CLASS VAPOR RETARDER CLASS
    CLIMATE ZONE Ia IIa III
    1, 2 Not permitted Not Permitted Permitted
    3 Not permitted Permittedc Permitted
    4 (except Marine) Not permitted Permittedc See Table 1404.3(3)
    Marine 4, 5, 6, 7, 8 Permittedb, c Permittedc See Table 1404.3(3)
    a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b.
  • § 0.625 High relevance — show source text

    875b| |Unit masonry|0.625b| |Cast-in-place or precast concrete|0.625b| |Two-coat work over:|| |Unit masonry|0.5b| |Cast-in-place or precast concrete|0.375b| |Terra cotta (anchored)|1| |Terra cotta (adhered)|0.25| |Vinyl siding|0.035| |Wood shingles|0.375| |Wood siding (without sheathing)a|0.5| |For SI: 1 inch = 25.4 mm, 1 ounce = 28.35 g, 1 square foot = 0.093 m2.
    a. Wood siding of thicknesses less than 0.5 inch shall be placed over sheathing that conforms to Section 2304.6.
    b. Exclusive of texture.
    c. As measured at the bottom of decorative grooves.
    d. 16 ounces per square foot for cold-rolled copper and lead-coated copper, 12 ounces per square foot for copper shingles, high-yield copper and lead-coated high-yield copper.|For SI: 1 inch = 25.4 mm, 1 ounce = 28.35 g, 1 square foot = 0.093 m2.
    a. Wood siding of thicknesses less than 0.5 inch shall be placed over sheathing that conforms to Section 2304.6.
    b. Exclusive of texture.
    c. As measured at the bottom of decorative grooves.
    d. 16 ounces per square foot for cold-rolled copper and lead-coated copper, 12 ounces per square foot for copper shingles, high-yield copper and lead-coated high-yield copper.|

    14-6 2025 CALIFORNIA BUILDING CODE

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

    EXTERIOR WALLS

    1404.3 Vapor retarders. Vapor retarder materials shall be classified in accordance with Table 1404.3(1). A vapor retarder shall be provided on the interior side of frame walls in accordance with Table 1404.3(2) and Tables 1404.3(3) or 1404.3(4) as applicable, or an approved design using accepted engineering practice for hygrothermal analysis. Vapor retarders shall be installed in accordance with Section 1404.3.2. The appropriate climate zone shall be selected in accordance with the California Energy Code .

    Exceptions:

    1. Basement walls.

    2. Below-grade portion of any wall.

    3. Construction where accumulation, condensation or freezing of moisture will not damage the materials.

    4. A vapor retarder shall not be required in Climate Zones 1, 2, and 3.

    5. In Climate Zones 4 through 8, a vapor retarder on the interior side of frame walls shall not be required where the assembly complies with Table 1404.3(5).

  • § 1404.3 High relevance — show source text
    TABLE 1404.3(2)—VAPOR RETARDER OPTIONS Col2 Col3 Col4
    CLIMATE ZONE VAPOR RETARDER CLASS VAPOR RETARDER CLASS VAPOR RETARDER CLASS
    CLIMATE ZONE Ia IIa III
    1, 2 Not permitted Not Permitted Permitted
    3 Not permitted Permittedc Permitted
    4 (except Marine) Not permitted Permittedc See Table 1404.3(3)
    Marine 4, 5, 6, 7, 8 Permittedb, c Permittedc See Table 1404.3(3)
    a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls with a Class I vapor retarder on the exterior side, use of a Class I interior vapor retarder that is not a responsive vapor retarder shall require an_approved_ design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing installed as continuous insulation on the exterior side of frame walls, the
    continuous insulation shall comply with Table 1404.3(4) and the Class I or II vapor retarder shall be a responsive vapor retarder.
    TABLE 1404.3(3)—CLASS III VAPOR RETARDERS Col2
    ZONE **CLASS III VAPOR RETARDERS PERMITTED FOR:a,
  • § 14-7 High relevance — show source text

    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. 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. 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. 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_.
    TABLE 1404.3(5)—CONTINUOUS INSULATION ON WALLS WITHOUT A CLASS I, II, OR III INTERIOR VAPOR RETARDERa Col2
    CLIMATE ZONE PERMITTED CONDITIONSb,c
    4 Continuous insulation with_R_-value ≥ 4.5
    5 Continuous insulation with_R_-value ≥ 6.5
    6 Continuous insulation with_R_-value ≥ 8.5
    7 Continuous insulation with_R_-value ≥ 11.5
    8 Continuous insulation with_R_-value ≥ 14
    a. The total insulating value of materials to the interior side of the exterior continuous insulation, including any cavity insulation, shall not exceed R-5. Where the_R_-value of
    materials to the interior side of the exterior continuous insulation exceeds R-5, an_approved_ design shall be required.
    b. A water vapor control material layer having a permeance of not greater than 1 perm in accordance with ASTM E96, Procedure A (dry cup) shall be placed on the exterior side
    of the wall and to the interior side of the exterior continuous insulation. The exterior continuous insulation shall be permitted to serve as the vapor control layer where, at its
    installed thickness or with a facer on its interior face, the exterior continuous insulation is a Class I or II vapor retarder.
    c.
  • California Energy Code High relevance — show source text
    TABLE R702.7(2)—VAPOR RETARDER OPTIONS Col2 Col3 Col4
    CLIMATE ZONE VAPOR RETARDER CLASS VAPOR RETARDER CLASS VAPOR RETARDER CLASS
    CLIMATE ZONE CLASS Ia CLASS IIa CLASS III
    1, 2 Not Permitted Not Permitted Permitted
    3, 4 (except Marine 4) Not Permitted Permittedc Permitted
    Marine 4, 5, 6, 7, 8 Permittedb, c Permittedc See Table R702.7(3)
    a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls, use of a Class I vapor retarder that is not a responsive vapor retarder on the interior side with a Class I vapor retarder on the exterior side shall require an
    approved design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing or insulated siding installed as continuous insulation on the exterior side of
    frame walls, the continuous insulation shall comply with Table R702.7(4) and the Class I or II vapor retarder shall be a responsive vapor retarder_._    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls, use of a Class I vapor retarder that is not a responsive vapor retarder on the interior side with a Class I vapor retarder on the exterior side shall require an
    approved design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing or insulated siding installed as continuous insulation on the exterior side of
    frame walls, the continuous insulation shall comply with Table R702.7(4) and the Class I or II vapor retarder shall be a responsive vapor retarder_._    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls, use of a Class I vapor retarder that is not a responsive vapor retarder on the interior side with a Class I vapor retarder on the exterior side shall require an
    approved design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing or insulated siding installed as continuous insulation on the exterior side of
    frame walls, the continuous insulation shall comply with Table R702.7(4) and the Class I or II vapor retarder shall be a responsive vapor retarder_._    		 a. A responsive vapor retarder shall be allowed on the interior side of any frame wall in all climate zones.
    b. In frame walls, use of a Class I vapor retarder that is not a responsive vapor retarder on the interior side with a Class I vapor retarder on the exterior side shall require an
    approved design.
    c. Where a Class I or II vapor retarder is used in combination with foam plastic insulating sheathing or insulated siding installed as continuous insulation on the exterior side of
    frame walls, the continuous insulation shall comply with Table R702.7(4) and the Class I or II vapor retarder shall be a responsive vapor retarder_._

    |TABLE R702.

  • § 25.4 High relevance — show source text

    @ 16″|—|32″
    (287)|25″
    (356)|36″
    (263)|29″
    (345)|21″
    (428)|29″
    (367)|20″
    (484)|—|23″
    (471)|—|—| |2 × 12 @ 12″|—|42″
    (209)|31″
    (263)|—|37″
    (253)|27″
    (317)|36″
    (271)|27″
    (358)|17″
    (447)|31″
    (348)|19″
    (462)|—| |2 × 12 @ 8″|—|48″
    (136)|45″
    (169)|—|48″
    (164)|38″
    (206)|—|40″
    (233)|26″
    (294)|36″
    (230)|29″
    (304)|18″
    (379)| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Tabulated values are for clear-span roof supported solely by exterior bearing walls.
    b. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir and spruce-pine-fir for repetitive (three or more) members.
    c. Ratio of backspan to cantilever span shall be not less than 3:1.
    d. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
    e. Uplift force is for a backspan to cantilever span ratio of 3:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 3 divided by the actual
    backspan ratio provided (3/backspan ratio).
    f. See Section R301.2.2.6, Item 1, for additional limitations on cantilevered floor joists for detached one- and two-family dwellings in Seismic Design Category D0, D1 or D2 and
    townhouses in Seismic Design Category C, D0, D1 or D2.
    g. Linear interpolation shall be permitted for building widths and ground snow loads other than shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Tabulated values are for clear-span roof supported solely by exterior bearing walls.
    b. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir and spruce-pine-fir for repetitive (three or more) members.
    c. Ratio of backspan to cantilever span shall be not less than 3:1.
    d. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
    e. Uplift force is for a backspan to cantilever span ratio of 3:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 3 divided by the actual
    backspan ratio provided (3/backspan ratio).
    f.

  • § 7.1 High relevance — show source text

    The total insulating value of materials to the interior side of the exterior continuous insulation, including any cavity insulation, shall not exceed R-5. Where the R-value of
    materials to the interior side of the exterior continuous insulation exceeds R-5, an approved design shall be required.
    b. A water vapor control material layer having a permeance not greater than 1 perm in accordance with ASTM E96 Procedure A (dry cup) shall be placed on the exterior side of
    the wall and to the interior side of the exterior continuous insulation. The exterior continuous insulation shall be permitted to serve as the vapor control layer where, at its
    installed thickness or with a facer on its interior face, the exterior continuous insulation is a Class I or II vapor retarder.
    c. The requirements in this table apply only to insulation used to control moisture in order to allow walls without a Class I, II or III interior vapor retarder. The insulation materi-
    als used to satisfy this option also contribute to but do not supersede the thermal envelope requirements of the_California Energy Code_.|a. The total insulating value of materials to the interior side of the exterior continuous insulation, including any cavity insulation, shall not exceed R-5. Where the R-value of
    materials to the interior side of the exterior continuous insulation exceeds R-5, an approved design shall be required.
    b. A water vapor control material layer having a permeance not greater than 1 perm in accordance with ASTM E96 Procedure A (dry cup) shall be placed on the exterior side of
    the wall and to the interior side of the exterior continuous insulation. The exterior continuous insulation shall be permitted to serve as the vapor control layer where, at its
    installed thickness or with a facer on its interior face, the exterior continuous insulation is a Class I or II vapor retarder.
    c. The requirements in this table apply only to insulation used to control moisture in order to allow walls without a Class I, II or III interior vapor retarder. The insulation materi-
    als used to satisfy this option also contribute to but do not supersede the thermal envelope requirements of the_California Energy Code_.|

    R702.7.1 Spray foam plastic insulation for moisture control with Class II and III vapor retarders. For purposes of compliance with Tables R702.7(3) and R702.7(4), spray foam with a maximum permeance of 1.5 perms at the installed thickness applied to the interior side of wood structural panels, fiberboard, insulating sheathing or gypsum shall be deemed to meet the continuous insulation moisture control requirement in accordance with one of the following conditions:

    1. The spray foam R -value is equal to or greater than the specified continuous insulation R -value.
    2. The combined R -value of the spray foam and continuous insulation is equal to or greater than the specified continuous insulation R -value.

    R702.7.2 Vapor retarder installation. Vapor retarders shall be installed in accordance with the manufacturer’s instructions, accepted installation methods or an approved design. Where a vapor retarder also functions as a component of a continuous air barrier, the vapor retarder shall be installed as an air barrier in accordance with Section N1102.5.1.1.

    R702.7.3 California Energy Code and International Energy Conservation Code Climate Zones. The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Table R702.7.3.

    |TABLE R702.7.3—IECC VS.

Frequently asked questions

What permeance test and procedure is referenced for the 1‑perm exterior control layer?

The code references ASTM E96, Procedure A (dry cup) for the exterior water vapor control material layer having permeance not greater than 1 perm in Table 1404.3(5).

Does the spray‑foam 1.5‑perm allowance apply to open‑cell and closed‑cell foam generically?

The code allowance in § 1404.3.1 is based on measured permeance at the installed thickness (≤ 1.5 perms). The code does not differentiate by foam trade name — compliance is demonstrated by the installed‑thickness permeance and meeting the R‑value conditions.

If a vapor retarder is also the air barrier, what must I do differently?

Install the vapor retarder as an air barrier in accordance with the California Energy Code (i.e., follow the Energy Code air‑barrier installation requirements in addition to the vapor‑retarder manufacturer’s instructions or an approved design). § 1404.3.2 requires this.

Are there climate zones where no interior vapor retarder is required?

Yes — Climate Zones 1, 2, and 3 do not require an interior vapor retarder under § 1404.3 exceptions. For Climate Zones 4–8 other options (Tables 1404.3(4) and 1404.3(5)) may permit omission if the wall assembly meets the listed continuous‑insulation or exterior control requirements.

What if my assembly has Class I vapor retarders on both sides of the wall?

The code flags this as a condition requiring an approved design (hygrothermal analysis or approved design) — do not assume two-sided Class I is acceptable without engineering review; see the notes and exceptions to Table 1404.3(2).

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Related in the California Energy Code

Continuous insulation R‑value requirements to allow interior vapor retarders (1404.3 tables)

Residential continuous insulation tables and limits (R702.7(4) and R702.7(5))

Vented cladding, moisture control and permitted continuous insulation conditions

Moisture control, continuous insulation and thermal‑bridging controls

California Energy Code