CBC · California Building Code
Which materials are permitted for exterior walls and what WRB materials are acceptable?
The CBC requires at least one continuous water‑resistive barrier behind every exterior wall veneer; acceptable WRBs are limited to No.15 felt (ASTM D226 Type 1), WRBs meeting ASTM E2556, foam‑insulating‑sheathing WRB systems that meet §1402.2, assemblies tested per ASTM E331, or other approved materials installed per the manufacturer's instructions. Laps and continuity (e.g., 2" horizontal lap and 6" joint lap for felt/ASTM E2556) plus proper flashing and termination are mandatory to meet the code (§ 1403.1; § 1403.2) file.
Last reviewed: July 5, 2026
What the code requires — 2-4 sentences
The CBC requires exterior wall materials to comply with Chapter 14 and permits alternatives only when approved; materials used for exterior walls must meet the specific provisions in Section 1403.1 (§ 1403.1). A continuous water‑resistive barrier (WRB) of not fewer than one layer must be installed behind the exterior veneer, attached to studs or sheathing, flashed as required, continuous to the top of the wall and terminated at penetrations/building appendages; acceptable WRB materials are limited to the options listed in § 1403.2 (§ 1403.2) .
Requirements in detail
1) General rule for exterior wall materials
- Materials used for the construction of exterior walls must comply with Chapter 14 material provisions; materials not specifically prescribed are allowed only if approved as an alternate in accordance with § 1403.1 (§ 1403.1) .
2) WRB: required performance and placement
- At least one layer of WRB is required and it must be attached to studs or sheathing and installed with flashing as described in § 1404.4. The WRB must provide a continuous barrier behind the exterior veneer, be continuous to the top of the wall, and be properly terminated at penetrations and appendages to meet the exterior wall envelope requirements in § 1402.2; intersections with fenestration must be flashed/assembled per the fenestration manufacturer's instructions or other approved methods (§ 1403.2) .
3) Acceptable WRB materials (explicit list from the code)
The WRB must comply with one of the listed options in § 1403.2:
- No. 15 felt complying with ASTM D226, Type 1.
- Sheet WRB complying with ASTM E2556, Type I or II.
- Foam plastic insulating‑sheathing WRB systems that comply with § 1402.2 and are installed according to the manufacturer’s instructions.
- Systems shown by testing to comply with ASTM E331 in accordance with § 1402.2.
- Other approved materials when installed per the manufacturer’s installation instructions (§ 1403.2) .
4) Installation detail required by the code (laps, orientation)
- When No. 15 asphalt felt or WRB complying with ASTM E2556 is used, the code requires horizontal application with the upper layer lapped over the lower layer by not less than 2 inches (51 mm). Where joints occur, the upper and lower layers must be lapped not less than 6 inches (152 mm) (§ 1403.2) .
Decision‑relevant table
| Decision factor | Acceptable value / requirement | Code reference |
|---|---|---|
| Minimum number of WRB layers | 1 layer (not fewer than one) | § 1403.2 |
| Acceptable WRB types | No. 15 felt (ASTM D226 Type 1); ASTM E2556 Type I/II; foam plastic insulating sheathing WRB systems (per § 1402.2); ASTM E331 assemblies (per § 1402.2); other approved per manufacturer | § 1403.2 |
| Horizontal lap (No.15 felt / ASTM E2556) | Upper over lower ≥ 2 in (51 mm) | § 1403.2 (lap requirement) |
| Lap at joints | Upper and lower layers ≥ 6 in (152 mm) | § 1403.2 (joint lap) |
| Continuity | Continuous to top of walls; terminated at penetrations/appendages | § 1403.2 |
| Attachment location | Attached to studs or sheathing | § 1403.2 |
Exceptions & special cases
- Alternatives: Materials not listed in Chapter 14 are permitted if approved as alternate materials under § 1403.1 (§ 1403.1) .
- Foam plastic insulating sheathing WRB systems and ASTM E331 tested assemblies are allowed only when they comply with § 1402.2 and are installed per manufacturer instructions (§ 1403.2) .
- The WRB requirements may be superseded when an exterior wall assembly has been demonstrated by ASTM E331 testing to resist wind‑driven rain for the full assembly (see § 1402.2 referencing ASTME331 test conditions) — that testing path is addressed in § 1402.2 (see Related Provisions) .
If you need to use a WRB product not explicitly listed, the route is to supply documentation (manufacturer instructions, test reports or an approved listing) and obtain approval per the alternate‑materials process described in § 1403.1 (§ 1403.1) .
Common mistakes
- Installing WRB that is not continuous to the top of wall or failing to properly terminate at penetrations — violates the continuity/termination requirement in § 1403.2 (§ 1403.2) .
- Applying No. 15 felt or ASTM E2556 sheets without the required laps (2" horizontal lap; 6" joint lap) — laps are mandatory for those materials (§ 1403.2) .
- Assuming a rainscreen cavity removes WRB requirements — § 1403.2 requires a WRB behind the veneer unless the assembly is specifically demonstrated to resist wind‑driven rain per accepted testing (see § 1402.2 for the testing route) .
- Using a product as a WRB that does not meet one of the listed standards (ASTM D226, ASTM E2556, ASTM E331 where applicable) or without an approved manufacturer installation — the code limits acceptable WRBs to those listed or other approved materials installed per manufacturer instructions (§ 1403.2) .
- Confusing WRB and vapor retarders: WRB is a drainage/penetration control layer required behind cladding per § 1403.2; vapor retarder requirements are addressed elsewhere in Chapter 14 (§ 1404.3) and have different performance criteria .
Worked example
Scenario: A 2‑story, wood‑framed house with exterior fiber‑cement lap siding. The contractor intends to use No. 15 asphalt felt as the WRB.
Step-by-step application required by the CBC:
- Provide not fewer than one layer of No. 15 felt attached to the sheathing (minimum one WRB layer) — § 1403.2 requires at least one layer .
- Install the felt horizontally so that each upper course laps the lower course by at least 2 inches (51 mm) — § 1403.2 horizontal lap requirement .
- At vertical joints (end joints) ensure the upper and lower layer laps are at least 6 inches (152 mm) — § 1403.2 joint lap requirement .
- Flash all fenestration per the window manufacturer’s installation instructions and integrate the WRB into those flashings (the intersection must be flashed and assembled per the fenestration manufacturer or other approved methods) — § 1403.2 .
- Make the felt continuous to the top of the wall and terminate neatly around penetrations and appendages so the exterior wall envelope requirements of § 1402.2 are met — § 1403.2 referencing § 1402.2 .
Concrete numbers recap: horizontal laps ≥ 2 in (51 mm); joints laps ≥ 6 in (152 mm); at least 1 layer of No. 15 felt — meet each of these to comply with § 1403.2 .
Related provisions
- § 1402.2 — Weather protection / water‑resistive barrier and drainage requirements (assembly performance context) .
- § 1404.4 — Flashing requirements (WRB installation must include flashing as described in § 1404.4) .
- § 1404.3 — Vapor retarder classification and interior vapor‑retarder requirements (distinguish vapor retarders from WRBs) .
- § 1402.6 — Combustibility/testing requirements for combustible WRBs on tall buildings (when WRB combustibility matters) .
- Table 1404.2 / § 1404.2 — Minimum thickness of weather coverings and what constitutes acceptable weather coverings (relevant when the WRB is the only combustible component) .
Code references
Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:
CBC § 1403.1 High relevance — show source text
SECTION 1403—MATERIALS
1403.1 General. Materials used for the construction of exterior walls shall comply with the provisions of this section. Materials not prescribed herein shall be permitted, provided that any such alternative has been approved.
1403.2 Water-resistive barrier. Not fewer than one layer of water-resistive barrier material shall be attached to the studs or sheathing, with flashing as described in Section 1404.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer. The intersection between the water-resistive barrier material and fenestration openings shall be flashed and assembled in accordance with the fenestration manufacturer’s installation instructions, or other approved methods for applications not addressed by the fenestration manufacturer’s instructions. The water-resistive barrier material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section 1402.2.
Water-resistive barriers shall comply with one of the following:
No. 15 felt complying with ASTM D226, Type 1.
ASTM E2556, Type I or II.
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EXTERIOR WALLS
Foam plastic insulating sheathing water-resistive barrier systems complying with Section 1402.2 and installed in accordance with manufacturer’s installation instructions.
ASTM E331 in accordance with Section 1402.2.
Other approved materials installed in accordance with the manufacturer’s installation instructions.
No. 15 asphalt felt and water-resistive barriers complying with ASTM E2556 shall be applied horizontally with the upper layer lapped over the lower layer not less than 2 inches (51 mm). Where joints occur, the upper and lower layer shall be lapped not less than 6 inches (152 mm).
[BS] 1403.3 Wood. Exterior walls of wood construction shall be designed and constructed in accordance with Chapter 23.
[BS] 1403.3.1 Basic hardboard. Basic hardboard shall conform to the requirements of ANSI A135.4.
[BS] 1403.3.2 Hardboard siding. Hardboard siding shall conform to the requirements of ANSI A135.6 and, where used structurally, shall be so identified by the label of an approved agency.
[BS] 1403.4 Masonry. Exterior walls of masonry construction shall be designed and constructed in accordance with this section and Chapter 21. Masonry units, mortar and metal accessories used in anchored and adhered veneer shall meet the physical requirements of Chapter 21. The backing of anchored and adhered veneer shall be of concrete, masonry, steel framing or wood framing. Continuous insulation meeting the applicable requirements of this code shall be permitted between the backing and the masonry veneer.
[BS] 1403.5 Metal. Exterior walls constructed of cold-formed or structural steel shall be designed in accordance with Chapter 22. Exterior walls constructed of aluminum shall be designed in accordance with Chapter 20.
[BS] 1403.5.1 Aluminum siding. Aluminum siding shall conform to the requirements of AAMA 1402.
[BS] 1403.5.2 Cold-rolled copper. Copper shall conform to the requirements of ASTM B370.
CBC § 3.6.3 High relevance — show source text
BL104.3.6.3 Rain-exposed. Clay plaster, where exposed to rain, shall be finished with an approved erosion-resistant finish.
BL104.3.6.4 Prohibited finish coat. Plaster containing Portland cement shall not be permitted as a finish coat over clay plasters.
BL104.3.7 Clay-lime plaster. Clay-lime plaster shall be composed of refined clay or clay subsoil, sand and lime.
BL104.3.8 Hemp-lime plaster. Hemp-lime plaster shall be composed of hemp hurd and lime and shall be permitted to contain sand or other aggregate, and pozzolans.
BL104.3.9 Hemp-clay plaster. Hemp-clay plaster shall be composed of hemp hurd and clay or clay subsoil and shall be permitted to contain sand or other aggregate.
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APPENDIX BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
BL104.4 Separation of wood and plaster. Wood framing at the exterior surface of hemp-lime walls shall be separated from exterior plaster with Grade D paper or other approved material, except where the wood is naturally durable.
Exception: Exterior clay plaster shall not be required to be separated from wood.
BL104.5 Bridging across dissimilar substrates. Bridging shall be installed onto and across dissimilar substrates prior to the application of plaster on the interior or exterior. Acceptable bridging materials include expanded metal lath, woven wire mesh, welded wire mesh, fiberglass mesh, reed mat, burlap or other approved materials. Bridging shall extend not less than 3 inches (76 mm) on both sides of the juncture.
BL104.5.1 Returns on recessed openings. Plaster or other exterior finish returns at recessed windows and doors shall require an approved design that prevents the intrusion of moisture.
BL104.6 Nonplaster exterior cladding. Nonplaster exterior cladding shall be spaced not less than 1 inch (25 mm) from the face of the water-resistive barrier or air barrier to the back of the cladding to allow for ventilation. The ventilation space shall be open at the top and bottom and be provided with insect screening.
BL104.6.1 Water-resistive and air barriers. Water-resistive barriers and air barriers, when vapor permeable, are permitted to be applied directly to the hemp-lime when exterior cladding is installed in accordance with Section BL104.6.
BL104.7 High moisture interior environments. Exterior hemp-lime walls enclosing showers or steam rooms shall be lined on the interior side with ceramic tiles on an approved tile backer board, ceramic tiles on a lime plaster, or a tadelakt finish.
SECTION BL105—FIRE RESISTANCE
BL105.1 Fire-resistance rating. Hemp-lime walls do not have a fire-resistance rating. Fire-resistance ratings for hemp-lime wall assemblies shall be determined by testing in accordance with ASTM E119 or UL 263.
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.|14-6 2025 CALIFORNIA BUILDING CODE
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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 0.1II 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 1.0III 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 10TABLE 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 § 2303.2 High relevance — show source text
- Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane. Exceptions:
- Metal composite material (MCM) systems complying with Section 1406.
- Exterior insulation and finish systems (EIFS) complying with Section 1407.
- High-pressure decorative exterior-grade compact laminate (HPL) systems complying with Section 1408.
- Exterior wall coverings containing foam plastic insulation complying with Section 2603.
- Combustible exterior wall coverings constructed of fire-retardant-treated wood complying with Section 2303.2 for exterior installation shall not be limited in wall surface area where the fire separation distance is 5 feet (1524 mm) or less and shall be permitted up to 60 feet (18 288 mm) in height above grade plane regardless of the fire separation distance.
- Wood veneers shall comply with Section 1404.6.
1405.1.1.1 Ignition resistance. Where permitted by Section 1405.1.1, combustible exterior wall coverings shall be tested in accordance with NFPA 268.
Exceptions:
- Wood or wood-based products.
- Other combustible materials covered with an exterior weather covering, other than vinyl sidings, included in and complying with the thickness requirements of Table 1404.2.
- Aluminum having a minimum thickness of 0.019 inch (0.48 mm).
1405.1.1.1.1 Fire separation 5 feet or less. Where installed on exterior walls having a fire separation distance of 5 feet (1524 mm) or less, combustible exterior wall coverings shall not exhibit sustained flaming as defined in NFPA 268.
1405.1.1.1.2 Fire separation greater than 5 feet. For fire separation distances greater than 5 feet (1524 mm), any exterior wall covering shall be permitted that has been exposed to a reduced level of incident radiant heat flux in accordance with the NFPA 268 test method without exhibiting sustained flaming. The minimum fire separation distance required for the exterior wall covering shall be determined from Table 1405.1.1.1.2 based on the maximum tolerable level of incident radiant heat flux that does not cause sustained flaming of the exterior wall covering.
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EXTERIOR WALLS
CBC § 1403.11.2 High relevance — show source text
1403.11.2 Fire separation distance. The fire separation distance between a building with polypropylene siding and the adjacent building shall be not less than 10 feet (3048 mm).
1403.12 Foam plastic insulation. Foam plastic insulation used in exterior wall assemblies shall comply with Chapter 26.
1403.13 Fiber-mat reinforced cementitious backer units. Fiber-mat reinforced cementitious backer units used as an exterior substrate for the application of exterior finish materials shall comply with ASTM C1325.
1403.14 Insulated vinyl siding. Insulated vinyl siding shall be certified and labeled as conforming to the requirements of ASTM D7793 by an approved agency.
SECTION 1404—INSTALLATION OF WALL COVERINGS
1404.1 General. Exterior wall coverings shall be designed and constructed in accordance with the applicable provisions of this section.
1404.1.1 Soffits and fascias. Soffits and fascias installed as part of roof overhangs shall comply with Section 1412.
1404.1.2 Additional requirements. [DSA-SS, DSA-SS/CC, OSHPD 1, 1R, 2, 4 & 5] In addition to the requirements of Section 1404, the installation of anchored or adhered veneer shall comply with applicable provisions of Section 1413.
1404.2 Weather protection. Exterior walls shall provide weather protection for the building. The materials of the minimum nominal thickness specified in Table 1404.2 shall be acceptable as approved weather coverings.
2025 CALIFORNIA BUILDING CODE 14-5
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EXTERIOR WALLS
TABLE 1404.2—MINIMUM THICKNESS OF WEATHER COVERINGS Col2 COVERING TYPE MINIMUM THICKNESS (inches) Adhered masonry veneer 0.25 Aluminum siding 0.019 Anchored masonry veneer Stone (natural) 2.0 Architectural cast stone 2.5 Other 2.0 Asbestos-cement boards 0.125 Asbestos shingles 0.156 Cold-rolled copperd 0.0216 nominal Copper shinglesd 0.0162 nominal Exterior plywood (with sheathing) 0.313 Exterior plywood (without sheathing) See Section 2304.6 Fiber cement lap siding 0.25c Fiber cement panel siding 0.25c Fiberboard siding 0.5 Fiber-mat reinforced cementitious backer units 0.5 Glass-fiber reinforced concrete panels 0.375 Hardboard sidingc 0.25 High-yield copperd 0.0162 nominal Lead-coated copperd 0.0216 nominal Lead-coated high-yield copper 0.0162 nominal Marble slabs 1 Particleboard (with sheathing) See Section 2304.6 Particleboard (without sheathing) See Section 2304.6 Porcelain tile 0.125 nominal Steel (approved corrosion resistant) 0.0149 Structural glass 0.344 Stucco or exterior cement plaster Three-coat work over: Metal plaster base 0. CBC § 14-3 High relevance — show source text
1402 Performance Requirements . . . . . . . . . . . . . . . . . . . . 14-3
1403 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
1404 Installation of Wall Coverings. . . . . . . . . . . . . . . . . . . 14-5
1405 Combustible Materials on the Exterior Side of
Exterior Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
1406 Metal Composite Material (MCM). . . . . . . . . . . . . . . 14-17
1407 Exterior Insulation and Finish Systems (EIFS). . . . 14-18
1408 High-Pressure Decorative Exterior-Grade Compact Laminates (HPL). . . . . . . . . . . . . . . . . . . 14-18
1409 Insulated Metal Panel (IMP) . . . . . . . . . . . . . . . . . . . 14-19
1410 Plastic Composite Decking . . . . . . . . . . . . . . . . . . . . 14-21 1411 Building-Integrated Photovoltaic (BIPV) Systems for Exterior Wall Coverings and Fenestration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
1412 Soffits and Fascias at Roof Overhangs . . . . . . . . . . 14-21
1413 [DSA-SS & DSA-SS/CC, OSHPD 1, 1R, 2, 4 & 5] Additional Requirements for Anchored and Adhered Veneer. . . . . . . . . . . . . . 14-23
CHAPTER 15 ROOF ASSEMBLIES AND ROOFTOP
STRUCTURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
1501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1502 Roof Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1503 Weather Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1504 Performance Requirements . . . . . . . . . . . . . . . . . . . . 15-3
1505 Fire Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
1506 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
1507 Requirements for Roof Coverings . . . . . . . . . . . . . . . 15-7
CBC § 12-113 High relevance — show source text
1248 Reserved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-113
1249 Reserved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-113
1250 [CA] Pharmacies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-113
1251 [CA] Veterinary Premises . . . . . . . . . . . . . . . . . . . . . . 12-113
1252 [CA] Barber Colleges and Shops. . . . . . . . . . . . . . . . 12-114
1253 [CA] Schools of Cosmetology, Cosmetological Establishments and Satellite Classrooms . . . . . 12-114
1254 [CA] Acupuncture Offices . . . . . . . . . . . . . . . . . . . . . . 12-115
CHAPTER 13 ENERGY EFFICIENCY . . . . . . . . . . . . . . . . . . 13-1
CHAPTER 14 EXTERIOR WALLS . . . . . . . . . . . . . . . . . . . . . 14-1
1401 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3
1402 Performance Requirements . . . . . . . . . . . . . . . . . . . . 14-3
1403 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
1404 Installation of Wall Coverings. . . . . . . . . . . . . . . . . . . 14-5
1405 Combustible Materials on the Exterior Side of
Exterior Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
1406 Metal Composite Material (MCM). . . . . . . . . . . . . . . 14-17
1407 Exterior Insulation and Finish Systems (EIFS). . . . 14-18
1408 High-Pressure Decorative Exterior-Grade Compact Laminates (HPL). . . . . . . . . . . . . . . . . . . 14-18
1409 Insulated Metal Panel (IMP) . . . . . . . . . . . . . . . . . . . 14-19
1410 Plastic Composite Decking . . . . . . . . . . . . . . . . . . . . 14-21 1411 Building-Integrated Photovoltaic (BIPV) Systems for Exterior Wall Coverings and Fenestration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
CBC § 1404.6. High relevance — show source text
- Wood veneers shall comply with Section 1404.6.
1405.1.1.1 Ignition resistance. Where permitted by Section 1405.1.1, combustible exterior wall coverings shall be tested in accordance with NFPA 268.
Exceptions:
- Wood or wood-based products.
- Other combustible materials covered with an exterior weather covering, other than vinyl sidings, included in and complying with the thickness requirements of Table 1404.2.
- Aluminum having a minimum thickness of 0.019 inch (0.48 mm).
1405.1.1.1.1 Fire separation 5 feet or less. Where installed on exterior walls having a fire separation distance of 5 feet (1524 mm) or less, combustible exterior wall coverings shall not exhibit sustained flaming as defined in NFPA 268.
1405.1.1.1.2 Fire separation greater than 5 feet. For fire separation distances greater than 5 feet (1524 mm), any exterior wall covering shall be permitted that has been exposed to a reduced level of incident radiant heat flux in accordance with the NFPA 268 test method without exhibiting sustained flaming. The minimum fire separation distance required for the exterior wall covering shall be determined from Table 1405.1.1.1.2 based on the maximum tolerable level of incident radiant heat flux that does not cause sustained flaming of the exterior wall covering.
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TABLE 1405.1.1.1.2—MINIMUM FIRE SEPARATION FOR COMBUSTIBLE EXTERIOR WALL COVERINGS Col2 FIRE SEPARATION DISTANCE (feet) TOLERABLE LEVEL INCIDENT RADIANT HEAT ENERGY (kW/m2) 5 12.5 6 11.8 7 11.0 8 10.3 9 9.6 10 8.9 11 8.3 12 7.7 13 7.2 14 6.7 15 6.3 16 5.9 17 5.5 18 5.2 19 4.9 20 4.6 21 4.4 22 4.1 23 3.9 24 3.7 25 3.5 For SI: 1 foot = 304.8 mm, 1 Btu/H2 × °F = 0.0057 kW/m2 × K. For SI: 1 foot = 304.8 mm, 1 Btu/H2 × °F = 0.0057 kW/m2 × K. 1405.1.2 Location. Combustible exterior wall coverings located along the top of exterior walls shall be completely backed up by the exterior wall and shall not extend over or above the top of the exterior wall.
CBC § 1407.2 High relevance — show source text
1407.2
E2570/E2570M—07(2019): Standard Test Methods for Evaluating Water-Resistive Barrier (WRB) Coatings Used under Exterior Insulation and Finish Systems (EIFS) or EIFS with Drainage
1407.4.1.1, 1705.17.1
E2573—19: Standard Practice for Specimen Preparation and Mounting of Site-fabricated Stretch Systems to Assess Surface Burning Characteristics
803.10
E2579—21: Standard Practice for Specimen Preparation and Mounting of Wood Products to Assess Surface Burning Characteristics
803.11
E2599—2018: Standard Practice for Specimen Preparation and Mounting of Reflective Insulation, Radiant Barrier and Vinyl Stretch Ceiling Materials for Building Applications to Assess Surface Burning Characteristics
2614.3
E2632/E2632M—13: Standard Test Method for Evaluating the Under-Deck Fire Test Response of Deck Materials
709A.3, 709A.4, 709A.4.1, 709A.5
E2634—2018: Standard Specification for Flat Wall Insulating Concrete Form (ICF) Systems
1903.3
E2652—18: Standard Test Method for Assessing Combustibility of Materials Using a Tube Furnace with a Cone-shaped Airflow Stabilizer, at 750 [o] C
703.3.1
E2707—15: Standard Test Method for Determining Fire Penetration of Exterior Wall Assemblies Using a Direct Flame Impingement Exposure
707A.3, 707A.3.1, 708A.3
E2726/E2726—12a: Standard Test Method for Evaluating the Fire-Test-Response of Deck Structures to Burning Brands
709A.3, 709A.4, 709A.4.2
E2751/E2751M—2017A: Practice for Design and Performance of Supported Laminated Glass Walkways
2409.1
E2768—11(2018): Standard Test Method for Extended Duration Surface Burning Characteristics of Building Materials (30 min Tunnel Test)
2303.2.1
E2837—2013(2017): Standard Test Method for Determining the Fire Resistance of Continuity Head-of-Wall Joint Systems Installed Between Rated Wall Assemblies and Nonrated Horizontal Assemblies
715.6
E2925—19a: Standard Specification for Manufactured Polymeric Drainage and Ventilation Materials Used to Provide a Rainscreen Function
2510.6.2
E3121—17: Standard Test Methods for Field Testing of Anchors in Concrete or Masonry
1901.3.4.3, 1910A.5.2, 1909.2.6.2, 1909.2.6.5, 1910A.5.5
F547—2017: Terminology of Nails for Use with Wood and Wood-Base Materials
Table 2506.2
F606/F606M—21: Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets
2213.1, 2213A.1
CBC § 1407.4.1 High relevance — show source text
E2273—2018: Standard Test Method for Determining the Drainage Efficiency of Exterior Insulation and Finish Systems (EIFS) Clad Wall Assemblies
1407.4.1, 2510.6.2
E2307—20: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using the Intermediate-Scale, Multistory Test Apparatus
715.4
E2353—21: Standard Test Methods for Performance of Glazing in Permanent Railing Systems, Guards and Balustrades
2407.1.2
E2392 / E2392M—10(2016): Standard Guide for Design of Earthen Wall Building Systems
2109.2.4.8.9.2
E2393—20a: Standard Practice for On-Site Inspection of Installed Fire Resistive Joint Systems and Perimeter Fire Barriers
1705.18.2
E2404—17: Standard Practice for Specimen Preparation and Mounting of Textile, Paper or Polymeric (Including Vinyl) and Wood Wall or Ceiling Coverings, Facing and Veneers to Assess Surface Burning Characteristics
803.5.2, 803.12, 1402.6
E2556/E2556M—2010(2016): Standard Specification for Vapor Permeable Flexible Sheet Water-resistive Barriers Intended for Mechanical Attachment
1403.2, 2510.6.1
2025 CALIFORNIA BUILDING CODE 35-21
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
REFERENCED STANDARDS
E2568—2017A: Standard Specification for PB Exterior Insulation and Finish Systems
1407.2
E2570/E2570M—07(2019): Standard Test Methods for Evaluating Water-Resistive Barrier (WRB) Coatings Used under Exterior Insulation and Finish Systems (EIFS) or EIFS with Drainage
1407.4.1.1, 1705.17.1
E2573—19: Standard Practice for Specimen Preparation and Mounting of Site-fabricated Stretch Systems to Assess Surface Burning Characteristics
803.10
E2579—21: Standard Practice for Specimen Preparation and Mounting of Wood Products to Assess Surface Burning Characteristics
803.11
E2599—2018: Standard Practice for Specimen Preparation and Mounting of Reflective Insulation, Radiant Barrier and Vinyl Stretch Ceiling Materials for Building Applications to Assess Surface Burning Characteristics
2614.3
E2632/E2632M—13: Standard Test Method for Evaluating the Under-Deck Fire Test Response of Deck Materials
709A.3, 709A.4, 709A.4.1, 709A.5
E2634—2018: Standard Specification for Flat Wall Insulating Concrete Form (ICF) Systems
1903.3
E2652—18: Standard Test Method for Assessing Combustibility of Materials Using a Tube Furnace with a Cone-shaped Airflow Stabilizer, at 750 [o] C
703.3.1
E2707—15: Standard Test Method for Determining Fire Penetration of Exterior Wall Assemblies Using a Direct Flame Impingement Exposure
707A.3, 707A.3.1, 708A.3
CBC § 1402.7 High relevance — show source text
1402.7 Exterior wall veneers manufactured using combustible adhesives. Exterior wall assemblies on buildings of Type I, II, III or IV construction that are greater than 40 feet (12 192 mm) in height above grade plane and contain an exterior wall veneer manufactured using a combustible adhesive to laminate a metal core with noncombustible facing materials shall be tested in accordance with, and comply with, the acceptance criteria of NFPA 285, with the adhesive level at the maximum application rate intended for use. Combustibility shall be determined in accordance with Section 703.3.
1402.8 Vertical and lateral flame propagation compliance methods. When exterior wall assemblies are required in this chapter to be tested for vertical and lateral flame propagation in accordance with and comply with the acceptance criteria of NFPA 285, compliance with the requirements shall be established by any of the following:
- An exterior wall assembly tested in accordance with and meeting the acceptance criteria of NFPA 285.
- An exterior wall assembly design listed by an approved agency for compliance with NFPA 285.
- An approved analysis based on an assembly or condition tested in accordance with and meeting the acceptance criteria of NFPA 285.
[BS] 1402.9 Flood resistance. For buildings in flood hazard areas as established in Section 1612.3, exterior walls extending below the elevation required by Section 1612 shall be constructed with flood-damage-resistant materials.
[BS] 1402.10 Flood resistance for coastal high-hazard areas and coastal A zones. For buildings in coastal high-hazard areas and coastal A zones as established in Section 1612.3, electrical, mechanical and plumbing system components shall not be mounted on or penetrate through exterior walls that are designed to break away under flood loads.
SECTION 1403—MATERIALS
1403.1 General. Materials used for the construction of exterior walls shall comply with the provisions of this section. Materials not prescribed herein shall be permitted, provided that any such alternative has been approved.
1403.2 Water-resistive barrier. Not fewer than one layer of water-resistive barrier material shall be attached to the studs or sheathing, with flashing as described in Section 1404.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer. The intersection between the water-resistive barrier material and fenestration openings shall be flashed and assembled in accordance with the fenestration manufacturer’s installation instructions, or other approved methods for applications not addressed by the fenestration manufacturer’s instructions. The water-resistive barrier material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section 1402.2.
Water-resistive barriers shall comply with one of the following:
No. 15 felt complying with ASTM D226, Type 1.
ASTM E2556, Type I or II.
14-4 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
EXTERIOR WALLS
Foam plastic insulating sheathing water-resistive barrier systems complying with Section 1402.2 and installed in accordance with manufacturer’s installation instructions.
ASTM E331 in accordance with Section 1402.2.
Other approved materials installed in accordance with the manufacturer’s installation instructions.
CBC § 12-7 High relevance — show source text
SFM STANDARD 12-7A-3
12-7A-3.1 Application. The minimum design, construction and performance standards set forth herein for the exposed underside of horizontal projections such as the horizontal soffits of roof eaves, floor projections and exposed underfloor areas are those deemed necessary to establish conformance to the provisions of these regulations. Materials and assemblies that meet the performance criteria of this standard are acceptable for use as defined in the California Building Standards Code.
12-7A-3.2 Scope. This standard evaluates the fire-resistive performance of horizontal projection assemblies including the horizontal soffits of roof eaves, floor projections and exposed underfloor areas when subjected to direct flame exposure to the underside of a horizontal projection.
12-7A-3.3 Referenced documents.
ASTM D4442, Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials.
ASTM D4444, Test Methods for Use and Calibration of Hand-Held Moisture Meters.
California Building Code, Chapter 7A.
12-7A-3.4 Definitions.
- Eaves. A projecting edge of a roof that extends beyond the supporting wall as in CBC 702A “Roof Eave” or similar horizontal projection assembly.
- Soffit. The enclosed underside of any exterior overhanging section of a roof eave or similar horizontal projection assembly (see CBC 702A “Roof Eave Soffit”).
12-7A-3.5 Equipment.
- Burner. A 12 by 12-inch (300 by 300 mm) diffusion burner shall be used. Natural gas, methane or propane shall be supplied to the burner through a metered control system. The gas supply to the burner shall produce a net heat output of 300 ± 15 kW throughout the flame exposure. Burner output can be determined from HRR or calculated from the gas flow rate, temperature and pressure.
- Infrared temperature analyzer (optional). Intended for monitoring the temperature change of the inside of the eaves.
- Moisture content. Prior to testing, all materials (lumber and soffit material) shall be conditioned to a constant weight or for a minimum of 30 days at 73 ± 4°F (23 ± 2°C) and 50 ± 5% relative humidity, whichever occurs first. Constant weight shall be defined as occurring when the change in test material weight is less than or equal to 2 percent in a 24-hour period. Lumber moisture content shall be between 8 and 12 percent (oven-dry basis) and sheathing shall not exceed 8 percent (oven-dry basis).
12-7A-3.6 Materials.
Framing. The materials used shall be representative of the grades that would be typical of eave construction and installed in the eave’s subassembly as per accepted construction practices.
Soffit. Material selected for the test.
12-7A-3.7 Test system preparation (Figure 1).
- Eaves fabrication. The 4-foot-wide by 2-foot (1.2 m by 0.6 m) test specimen shall be constructed to fit into a 4-foot-wide (1.2 m) space at the top of the test assembly described in SFM 12-7A-1.
Frequently asked questions
Is a rainscreen cavity a substitute for a WRB?
No. A rainscreen provides drainage/venting but the CBC still requires a continuous WRB behind the veneer unless the entire wall assembly has been tested and shown to resist wind‑driven rain per the ASTM E331 testing path described in § 1402.2 and § 1403.2 file.
Can I use a product not listed in § 1403.2 as a WRB?
Yes, but only if it is approved as an alternate or is an “other approved material” installed per the manufacturer's instructions; § 1403.1 permits alternative materials only with approval, and § 1403.2 allows other approved materials when installed per manufacturer instructions (§ 1403.1; § 1403.2) .
How many layers of felt are required?
The code requires not fewer than one layer of WRB. When using No. 15 felt, at least one layer is required and must be installed with the laps required by § 1403.2 (2" horizontal, 6" at joints) (§ 1403.2) file.
Do WRB requirements change for tall, multi‑story buildings?
Combustibility and special testing of some components (including WRBs) are addressed elsewhere (for example § 1402.6) where combustible WRBs on buildings over 40 ft may require testing to NFPA 285 or meet other test criteria — check § 1402.6 for those limits in addition to § 1403.2 requirements .
If I use an ASTM E2556 WRB, do the lap rules apply?
Yes. The code specifically states that No. 15 asphalt felt and WRBs complying with ASTM E2556 must be applied horizontally with upper layer lapped over lower not less than 2 inches and joints lapped not less than 6 inches (§ 1403.2) .
More in California Building Code
- Administration & Permits
- Energy Efficiency
- Existing Buildings
- Occupancy Classification & Use
- Hazardous Materials & Occupancies
- Types of Construction
- Fire-Resistance & Fire Safety
- Interior Finishes
- Means of Egress
- Accessibility
- Exterior Walls
- Roofing & Roof Assemblies
- Structural Design
- Special Inspections & Tests
- Foundations & Soils
- Concrete
- Masonry
- Steel
- Wood
- Elevators & Conveying Systems
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