CBC · California Building Code

How is condensation and vapor control addressed in exterior wall assemblies?

The CBC requires controlling condensation in exterior walls by using vapor retarders (Class I–III) or qualifying exterior continuous insulation per the climate‑zone rules in § 1404.3 and its tables; installers must follow manufacturer instructions, meet R‑value thresholds when relying on continuous insulation, and still provide proper WRB, drainage and flashing to prevent moisture damage.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code requires protection against condensation in exterior wall assemblies by controlling water‑vapor flow with vapor retarders and/or appropriately located continuous insulation and by following the vapor‑retarder options set out for each climate zone in § 1404.3 and its Tables 1404.3(1)–(5) (§ 1404.3) . Vapor retarder materials are classified by permeance and must be installed per the manufacturer or an approved design (§ 1404.3.1, § 1404.3.2) . Where continuous exterior insulation is used it may serve as the vapor control layer if it meets the specified Class and R‑value criteria in the tables (§ 1404.3, Tables 1404.3(3)–(5)) . Weather protection measures (WRB, drainage and flashing) are required in concert with vapor control (see § 1402.2 and § 1404.4) .

If you use exterior continuous insulation to avoid an interior vapor retarder, the code limits the total insulating value on the interior side of that exterior insulation (e.g., total interior side R must not exceed R‑5 unless approved design) — see Table 1404.3(5) notes (§ 1404.3 table notes) .

Common mistakes

Misclassifying materials by perm: using a material thought to be Class II but testing at >1.0 perm (so actually Class III) — check ASTM E96 permeance values against Table 1404.3(1) (§ 1404.3) .
Installing a tight (Class I) interior vapor barrier in a climate or assembly where it is not permitted or without an approved design; this can trap moisture in cold sheathing and cause decay (§ 1404.3 and tables) .
Assuming continuous exterior insulation always removes need for any interior control — you must meet the R‑value and installation requirements in the applicable table (Tables 1404.3(4)–(5)) and the interior side total R limit where applicable (§ 1404.3, Tables) .
Failing to follow manufacturer installation instructions or Energy Code requirements when the vapor retarder also serves as the air barrier (§ 1404.3.2) .
Forgetting coordination with WRB/drainage and flashing — vapor control is one element; water management per § 1402.2 and flashing per § 1404.4 are also required .

Worked example — 2×6 wood framed exterior wall in Climate Zone 6

Project: New 2×6 framed exterior wall in Climate Zone 6.

Option A — interior vapor retarder path (straightforward):

Provide an interior Class II vapor retarder (e.g., kraft‑faced batt or an approved vapor‑retarder paint with permeance ≤ 1.0 perm). Table 1404.3(2) permits Class II in higher zones; installation per manufacturer or approved design satisfies § 1404.3 and § 1404.3.2 .

Option B — use continuous exterior insulation to qualify as the vapor control layer:

Per Table 1404.3(4), for Climate Zones 4–6 a 2×6 wall with exterior continuous insulation must have continuous insulation R ≥ 5 to meet the Class I or II continuous‑insulation option. So specify exterior continuous insulation with R‑5 (or greater) and ensure the exterior CI is a Class I or II vapor retarder at installed thickness (or has a qualifying facer). With that exterior CI in place, the exterior insulation may be allowed to serve as the vapor control layer per the table notes (§ 1404.3; Table 1404.3(4)) .
If instead you choose to omit an interior VR under the Table 1404.3(5) path, note that for CZ6 Table 1404.3(5) requires continuous exterior insulation R ≥ 8.5 and limits the total insulating value of materials to the interior side of the exterior continuous insulation to R‑5 (unless an approved design is provided) — verify those limits before omitting the interior VR (§ 1404.3; Table 1404.3(5)) .

Additional requirements for either option:

Install the vapor retarder or exterior CI per manufacturer instructions or an approved hygrothermal design (§ 1404.3.2, § 1404.3) .
Provide the water‑resistive barrier, drainage plane and flashing required by § 1402.2 and § 1404.4 to prevent liquid water from reaching the assembly (§ 1402.2, § 1404.4) .

Related provisions

§ 1404.3 — Vapor retarders; Tables 1404.3(1)–(5) (primary controlling section)
§ 1404.3.1 — Spray foam and the 1.5‑perm allowance / R‑value conditions
§ 1404.3.2 — Vapor retarder installation requirements and air‑barrier coordination (Energy Code)
§ 1404.3.3 — Climate‑zone selection guidance (Calif. Energy Code / IECC mapping)
§ 1402.2 — Weather protection; requires protection against condensation by compliance with § 1404.3
§ 1404.4 — Flashing requirements complementary to vapor/moisture control (§ 1404.4)

Code references

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

CBC § 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.

CBC § 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.|

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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:

Basement walls.
Below-grade portion of any wall.
Construction where accumulation, condensation or freezing of moisture will not damage the materials.
A vapor retarder shall not be required in Climate Zones 1, 2, and 3.
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.

CBC § 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.

CBC § 2.5 High relevance — show source text

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 R702.7(3)—CLASS III VAPOR RETARDERS	Col2
CLIMATE ZONE	CLASS III VAPOR RETARDERS PERMITTED FOR:a, b
Marine 4	Vented cladding over wood structural panels.
Marine 4	Vented cladding over fiberboard.
Marine 4	Vented cladding over gypsum.
Marine 4	Continuous insulation with_R_-value ≥ 2.5 over 2 × 4 wall.
Marine 4	Continuous insulation with_R_-value ≥ 3.75 over 2 × 6 wall.
5	Vented cladding over wood structural panels.
5	Vented cladding over fiberboard.
5	Vented cladding over gypsum.
5	Continuous insulation with_R_-value ≥ 5 over 2 × 4 wall.
5	Continuous insulation with_R_-value ≥ 7.5 over 2 × 6 wall.
6	Vented cladding over fiberboard.
6	Vented cladding over gypsum.
6	Continuous insulation with_R_-value ≥ 7.5 over 2 × 4 wall.
6	Continuous insulation with_R_-value ≥ 11.25 over 2 × 6 wall.
7	Continuous insulation with_R_-value ≥ 10 over 2 × 4 wall.
7	Continuous insulation with_R_-value ≥ 15 over 2 × 6 wall.
8	Continuous insulation with_R_-value ≥ 12.5 over 2 × 4 wall. Continuous insulation with_R_-value ≥ 20 over 2 × 6 wall.
a.

CBC § 1401.1 High relevance — show source text
ICC code development note: Code change proposals to sections preceded by the designation [BS] will be considered by the IBC—Structural Code Development

Committee during the 2025 (Group B) Code Development Cycle.

SECTION 1401—GENERAL

1401.1 Scope. The provisions of this chapter shall establish the minimum requirements for exterior walls, exterior wall assemblies, exterior wall coverings, exterior wall openings, exterior windows and doors, exterior soffits and fascias, and architectural trim.

SECTION 1402—PERFORMANCE REQUIREMENTS

1402.1 General. The provisions of this section shall apply to exterior walls, exterior wall coverings and components thereof.

1402.2 Weather protection. Buildings shall be provided with a weather-resistant exterior wall assembly. The exterior wall assembly shall include flashing, as described in Section 1404.4. The exterior wall assembly shall be designed and constructed in such a manner as to prevent the accumulation of water within the exterior wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1404.3.

Exceptions:
1. A weather-resistant exterior wall assembly shall not be required over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively.
2. Compliance with the requirements for a means of drainage, and the requirements of Sections 1403.2 and 1404.4, shall not be required for an exterior wall assembly that has been demonstrated through testing to resist wind-driven rain, including joints, penetrations and intersections with dissimilar materials, in accordance with ASTM E331 under the following conditions:
The exterior wall design shall be considered to resist wind-driven rain where the results of testing, in accordance with ASTM E331, indicate that water did not penetrate control joints in the exterior wall, joints at the perimeter of openings or intersections of terminations with dissimilar materials.

2.1. Exterior wall test assemblies shall include not fewer than one opening, one control joint, one wall/eave interface and one wall sill. Tested openings and penetrations shall be representative of the intended end-use configuration. 2.2. Exterior wall test assemblies shall be not less than 4 feet by 8 feet (1219 mm by 2438 mm) in size. 2.3. Exterior wall test assemblies shall be tested at a minimum differential pressure of 6.24 pounds per square foot (0.297 kN/m [2] ). 2.4. Exterior wall test assemblies shall be subjected to a minimum test exposure duration of 2 hours. 3. Exterior insulation and finish systems (EIFS) complying with Section 1407.4.1.

1402.2.1 [BSC-CG] See California Green Building Standards Code, Chapter 5, Division 5.4 for additional weather protection requirements.

[BS] 1402.3 Wind resistance. Exterior walls, exterior wall coverings, exterior soffits and fascias, and the associated openings, shall be designed and constructed to resist safely the superimposed loads required by Chapter 16.

CBC § 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,

CBC § 1.2 High relevance — show source text
1_||X||||||||||||||||||||||| |1403|||X|||||||||||||||||||||| |1404|||X|||||||||||||||||||||| |1404.1.2||||||||X|X|X|X|X||X|X|||||||||| |1404.3.3|||||||||||||||||||||X|||| |1405|||X|||||||||||||||||||||| |1406|||X|||||||||||||||||||||| |1407|||X|||||||||||||||||||||| |1408|||X|||||||||||||||||||||| |1411|||X|||||||||||||||||||||| |1412|||X|||||||||||||||||||||| |1413||||||||X|X|X|X|X||X|X||||||||||

The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.

2025 CALIFORNIA BUILDING CODE 14-1

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14-2 2025 CALIFORNIA BUILDING CODE

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14 EXTERIOR WALLS

User notes:

About this chapter: Chapter 14 addresses requirements for exterior walls of buildings. Minimum standards for wall covering materials, such as material performance and fire resistance, installation of wall coverings and the ability of the wall to provide weather protection are provided. This chapter also contains limitations on the areas and heights of combustible wall coverings based on fire separation distances, radiant heat exposure and surface burning characteristics.

ICC code development note: Code change proposals to sections preceded by the designation [BS] will be considered by the IBC—Structural Code Development

Committee during the 2025 (Group B) Code Development Cycle.

SECTION 1401—GENERAL

1401.1 Scope. The provisions of this chapter shall establish the minimum requirements for exterior walls, exterior wall assemblies, exterior wall coverings, exterior wall openings, exterior windows and doors, exterior soffits and fascias, and architectural trim.

SECTION 1402—PERFORMANCE REQUIREMENTS

1402.1 General. The provisions of this section shall apply to exterior walls, exterior wall coverings and components thereof.

1402.2 Weather protection. Buildings shall be provided with a weather-resistant exterior wall assembly. The exterior wall assembly shall include flashing, as described in Section 1404.4. The exterior wall assembly shall be designed and constructed in such a manner as to prevent the accumulation of water within the exterior wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1404.3.

Exceptions:
1. A weather-resistant exterior wall assembly shall not be required over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively.
2. Compliance with the requirements for a means of drainage, and the requirements of Sections 1403.2 and 1404.4, shall not be required for an exterior wall assembly that has been demonstrated through testing to resist wind-driven rain, including joints, penetrations and intersections with dissimilar materials, in accordance with ASTM E331 under the following conditions:

CBC § 1404.3 High relevance — show source text

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. 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

CBC § 6.7.5 High relevance — show source text
FIGURE BL103.6.7.5—TYPICAL HEMP-LIME THICK LINING

BONDING COAT, WHERE

BL103.6.7.6 Minimum thickness at anchorage rails. The minimum thickness of hemp-lime between the exterior face of vertical anchorage rails and the finished face of hemp-lime shall be 3 inches (76 mm) or in accordance with the binder manufacturer’s specifications.

BL103.7 Moisture control. Hemp-lime assemblies shall be protected from water intrusion and damage in accordance with Sections BL103.7.1 through BL103.7.9.

BL103.7.1 Water-resistive barriers. Water-resistive barriers are prohibited on hemp-lime walls, except as permitted or required elsewhere in this appendix.

BL103.7.2 Vapor retarders. Vapor retarders are prohibited on hemp-lime walls, except as permitted or required elsewhere in this appendix.

BL103.7.3 Penetrations in hemp-lime walls. Penetrations in exterior hemp-lime walls shall be sealed with an approved sealant or gasket on the exterior side of the wall in all climate zones and on the interior side of the wall in Climate Zones 5, 6, 7, 8 and Marine 4, as defined in Chapter 11.

BL103.7.4 Horizontal surfaces. Hemp-lime walls and other hemp-lime assemblies shall be provided with a water-resistive barrier at weather-exposed horizontal surfaces. The water-resistive barrier shall be of a material and installation that will prevent water from entering the wall system. Horizontal surfaces shall include exterior window sills and sills at exterior niches. Horizontal surfaces shall be sloped not less than 1 unit vertical in 12 units horizontal (8-percent slope) and shall drain away from hemp-lime

APPENDIX BL-8 2025 CALIFORNIA RESIDENTIAL CODE

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APPENDIX BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION

walls and other assemblies. Where the water-resistive barrier is below the finish material, it shall be sloped not less than 1 unit vertical in 12 units horizontal (8-percent slope) and shall drain to the exterior surface of the hemp-lime wall’s vertical finish.

BL103.7.5 Air barrier. Exterior hemp-lime walls shall have a vapor-permeable air barrier on all exterior and interior surfaces, except as permitted or required elsewhere in this appendix. Plaster in accordance with Section BL104.3 shall be acceptable as an air barrier.

BL103.7.6 Separation of hemp-lime and earth or paved areas. Hemp-lime shall be not less than 8 inches (203 mm) above exposed earth or paved areas.

BL103.7.7 Separation of exterior plaster and earth or paved areas. Exterior plaster applied to hemp-lime shall be not less than 8 inches (203 mm) above exposed earth or paved areas.

BL103.7.8 Separation of hemp-lime and exterior plaster from foundation. Hemp-lime and exterior plaster shall be separated from the foundation with an approved moisture barrier.

BL103.7.9 Base of wall flashing. The outer face of exterior walls shall be flashed to prevent water intrusion at the base of the wall.

SECTION BL104—FINISHES
CBC § 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.

CBC § 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.

Frequently asked questions

What is a “responsive” vapor retarder and when can I use one?

A responsive vapor retarder is a material whose permeance increases at high humidity (so it blocks vapor when dry but allows diffusion when wet). The CBC allows a responsive vapor retarder on the interior side of any frame wall in all climate zones (Table 1404.3(2) footnote) .

Can exterior continuous insulation act as the vapor control layer?

Yes — exterior continuous insulation may serve as the vapor control layer when, at installed thickness or with an interior facer, it qualifies as a Class I or II vapor retarder and meets the R‑value thresholds in Tables 1404.3(4)–(5) as applicable (§ 1404.3 and table notes) .

Do I still need flashing and a WRB if I meet the vapor retarder requirements?

Yes. The CBC requires a water‑resistive barrier, means of drainage and flashing to prevent water accumulation in the wall (see § 1402.2 and § 1404.4) — vapor control does not replace liquid‑water management .

What if I plan to use closed‑cell spray foam on the interior side of sheathing?

The code allows spray foam with a maximum permeance of 1.5 perms at installed thickness to be treated as meeting the continuous‑insulation moisture control requirement when its R‑value meets the table conditions; manufacturer instructions and R‑value conditions in § 1404.3.1 must be met (§ 1404.3.1) .

Can I omit an interior vapor retarder by using lots of interior insulation?

No — if you omit an interior vapor retarder in favor of exterior continuous insulation you must meet the specific continuous insulation R‑value thresholds in Table 1404.3(5) and you must observe the limit on total interior‑side R (interior materials to the inside of the exterior CI generally must not exceed R‑5 unless an approved design is provided) (§ 1404.3; Table 1404.3(5)) .

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California Building Code