1403 Materials — 2025 California Building Code

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.

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:

1. No. 15 felt complying with ASTM D226, Type 1.

2. ASTM E2556, Type I or II.

14-4 2025 CALIFORNIA BUILDING CODE

EXTERIOR WALLS

3. Foam plastic insulating sheathing water-resistive barrier systems complying with Section 1402.2 and installed in accordance with manufacturer’s installation instructions.

4. ASTM E331 in accordance with Section 1402.2.

5. 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.

[BS] 1403.5.3 Lead-coated copper. Lead-coated copper shall conform to the requirements of ASTM B101.

[BS] 1403.6 Concrete. Exterior walls of concrete construction shall be designed and constructed in accordance with Chapter 19.

[BS] 1403.7 Glass-unit masonry Exterior walls of glass-unit masonry shall be designed and constructed in accordance with Chapter 21.

Vinyl siding shall be certified and labeled as conforming to the requirements of ASTM D3679 by an approved

agency.

Fiber-cement siding shall conform to the requirements of ASTM C1186, Type A (or ISO 8336, Category A), and shall be so identified on labeling listing an approved agency.

Exterior insulation and finish systems (EIFS) and exterior insulation and finish systems (EIFS) with drainage shall comply with Section 1407.

Polypropylene siding shall be certified and labeled as conforming to the requirements of ASTM D7254 and those of Section 1403.11.1 or 1403.11.2 by an approved agency. Polypropylene siding shall be installed in accordance with the requirements of Section 1404.18 and in accordance with the manufacturer’s instructions. Polypropylene siding shall be secured to the building so as to provide weather protection for the exterior walls of the building.

1403.11.1 Flame spread index. The certification of the flame spread index shall be accompanied by a test report stating that all portions of the test specimen ahead of the flame front remained in position during the test in accordance with ASTM E84 or UL 723.

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).

Foam plastic insulation used in exterior wall assemblies shall comply with Chapter 26.

Fiber-mat reinforced cementitious backer units used as an exterior substrate for the application of exterior finish materials shall comply with ASTM C1325.

Insulated vinyl siding shall be certified and labeled as conforming to the requirements of ASTM D7793 by an approved agency.