EXTERIOR WALLS

Section 1402 Definitions

Section 1403 Performance Requirements

Section 1404 Materials

Section 1405 Installation of Wall Coverings

Section 1406 Combustible Materials on the Exterior Side of Exterior Walls

Section 1407 Metal Composite Materials

Section 1408 Exterior Insulation and Finish Systems (EIFS)

Key Points

Section 1402 Definitions

The code intends by the definition of veneer that it be a nonstructural facing of masonry, concrete, metal, plastic, or similar approved material. It is intended to provide ornamentation, protection, or insulation. On this basis, face bricks that are laid with common bricks so as to provide a composite structural assembly are not considered veneer, as they act structurally along with the common bricks. To be considered veneer, a material must not act structurally with the backing insofar as the consideration of structural strength of the assembly is concerned. However, in many cases the veneer does act structurally with the backing, and problems can result if not constructed properly.

Veneer can be either adhered or anchored and either exterior or interior, depending on its method of attachment to the backing and whether or not it is applied to a weather-exposed surface. The definitions for all of the specific terms listed in this section are located in Chapter 2.

Section 1403 Performance Requirements

This section provides specifications for the protection of the interior of the building from weather; therefore, there are requirements for:

1.   Protection of the interior wall covering from moisture that penetrates the exterior wall covering.

2.   Flashing of openings in, or projections through, exterior walls.

3.   Vapor retarders used to resist the transmission of water vapor through the exterior envelope.

It is also necessary to provide for the removal of any water that may accumulate behind the exterior veneer. The code requires a means for draining water to the exterior that enters the assembly. The intent of the provision is to merely utilize the felt building paper and flashing to drain the water to the outside, rather than provide an air space between the siding and the water-resistant barrier. Thus, the practice of placing siding directly over the building paper is acceptable, provided flashing is correctly installed to direct water within the wall assembly to the exterior.

The code exempts the need for a weather-resistant wall envelope over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively. The International Building Code® (IBC®) requirements for weather coverings, flashings, and drainage are also not applicable where the exterior wall envelope has been tested in accordance with ASTM E 331 and shown to resist wind-driven rain. In addition, where an exterior insulation and finish system (EIFS) is installed in accordance with Section 1408.4.1, the requirements of Section 1403.2 need not be followed.

Testing has shown that the addition of a combustible water-resistive barrier can cause an exterior wall system to fail the NFPA 285 test, even if the wall had successfully passed the test prior to the addition of the barrier. Small-scale testing has shown that these types of materials can provide significant amounts of combustible fuel loading to a wall assembly. Therefore, exterior walls of those buildings required to have noncombustible exterior walls (Types I, II, III, and IV) must be tested in accordance with NFPA 285 where they contain a combustible water-resistive barrier and are over 40 feet (12,192 mm) in height. The use of this testing method is necessary to address the potential vertical and lateral flame spread that can occur either on or within exterior wall systems that contain combustible barriers. An exception is provided where the exterior wall covering is a specified noncombustible material, or where the barrier is limited in peak heat release rate, total heat release, effective heat of combustion, flame spread index, and smoke-developed index.

Section 1404 Materials

As most exterior wall coverings are permeable by moisture, the code requires that there should be a water-resistive barrier placed under the exterior wall covering and over the sheathing. The purpose of the barrier is to prevent moisture infiltration to the sheathing and subsequently the interior wall surfaces. The required water-resistive barrier is identified as at least one layer of No. 15 asphalt felt complying with ASTM D 226 for Type I felt. All necessary flashing must be installed as described in Section 1405.4 in order to complete the water-resistant envelope.

Section 1405 Installation of Wall Coverings

Exterior wall coverings are to be installed in accordance with the provisions of this section. Of primary concern are the types and thicknesses of the weather protection provided by the wall coverings. In addition, it is important that flashing be installed in those areas prone to leakage. Various types of veneer are addressed, including wood, masonry, stone, metal, glass, vinyl, fiber, and cement. The specifics for each veneer type are described in detail.

1405.2   Weather protection.   A broad range of exterior wall-covering materials is listed in Table 1405.2 as being satisfactory when utilized as protection against the elements of nature. Covering types addressed include wood and particleboard siding, wood shingles, stucco, anchored and adhered masonry veneer, aluminum and vinyl siding, stone, and structural glass. For most of the 35 types listed, the minimum required thickness for weather protection is mandated. In the case of particleboard and plywood without sheathing, reference is made to Chapter 23.

1405.3   Vapor retarders.   In order to protect against condensation in framed exterior wall assemblies of buildings constructed in the specified Climate Zones, complying vapor retarders are mandated. Table C301.1 in the International Energy Conservation Code® (IECC®) establishes the appropriate Climate Zones in the United States based on counties. Those counties designated as Zone 5, 6, 7, and 8, as well as those classified as Zone 4 Marine must be provided, with exceptions, with either a Class I or II vapor retarder on the interior side of any exterior framed walls. The use of Class III vapor retarders is also acceptable provided such retarders are set forth in Table 1405.3.1 for the appropriate Climate Zones.

In contrast, low-permeability vapor barriers are prohibited in warmer climate zones. By prohibiting the Class I and II retarders on the interior side of walls in Climate Zones 1 and 2, and the Class I retarders in Climate Zones 3 and 4, the IBC helps to address the problem where warmer moist air from the exterior enters into the wall and then is trapped and condenses against the cooler interior side of the wall. See Figure 1405-1. It should be noted that the provision does not prohibit these particular vapor retarders in the specified climate zones, but that it is simply mandating that they are not placed on the interior side of the wall. If the better vapor barriers are installed on the interior side of the wall in the warmer climates, a reversed vapor retarder is essentially created, which can lead to the moisture being trapped and condensed within the wall.

Figure 1405-1   Vapor retarders.

1405.4   Flashing.   The code requires that all points subject to the entry of moisture be appropriately flashed. Roof and wall intersections, as well as parapets, are especially troublesome, as are exterior wall openings exposed to the weather, and particularly, those exposed to wind-driven rain. Even though the code may not cover every potential situation that might occur, it intends that the exterior envelope of the building be weatherproofed so as to protect the interior from the weather. Furthermore, for buildings of human occupancy, the interior must be sanitary and livable. Therefore, whether prescribed in the code or not, any place on the envelope of the building that provides a route for admission of water or moisture into the building is required to be properly protected.

Section 1406 Combustible Materials on the Exterior Side of Exterior Walls

Exterior walls of buildings of Types I, II, III, and IV are typically required to be of noncombustible construction. However, it is common for some limited combustible elements to be installed on the exterior side of such exterior walls. Type V buildings are permitted to use combustible materials for the entire wall construction. Where the exterior walls of a building include combustible materials such as wall coverings, trim, balconies, and similar appendages, the materials must be in compliance with this section. The only exception is for plastics, which are regulated by Chapter 26. The installation of such materials in compliance with the code does not negatively impact the desired level of fire safety.

The general requirements address the ignition resistance of the combustible wall coverings, based on the distance between the exterior wall and the lot line. Where the fire separation distance is 5 feet (1,524 mm) or less, the combustible wall covering must be subjected to the test method of NFPA 268 and exhibit no sustained flaming. As the exterior wall is moved farther and farther from the lot line, the tolerance to radiant heat energy need not be as great, allowing the use of alternative materials. Table 1406.2.1.1.2 identifies the tolerable level of incident radiant heat energy based on fire separation distance.

Section 1406.2.1 provides for the use of combustible wall coverings on otherwise noncombustible exterior walls, provided the building is limited to 40 feet (12,192 mm) in height above grade plane. The amount of such materials is also limited where the fire separation distance is 5 feet (1,524 mm) or less. The reductions from the general requirements are granted because of the restricted height and, in some cases, the limited amount of combustible materials. At a height exceeding 40 feet (12,192 mm), the use of combustible materials or supports is prohibited, except where the use of wood veneer and fire-retardant-treated wood is specifically allowed.

Balconies and similar projecting elements in buildings of Type I and II construction are to be constructed of noncombustible materials, unless the building is no more than three stories in height above grade plane. Under this condition, fire-retardant-treated wood may be used where the balcony or similar element is not used as a required egress path. Unless constructed of complying heavy-timber members, a combustible balcony or similar combustible projection must have a minimum fire-resistance rating equivalent to the required floor construction.

In Type III, IV, and V buildings, balcony construction may be of any material permitted by the code, combustible or noncombustible. Where a fire-resistance rating is mandated by the code, it must be maintained at the projecting element unless sprinkler protection is provided or it is of Type IV construction.

In addition to these types of construction limitations, the aggregate length of all projections cannot exceed 50 percent of the building perimeter at each floor unless sprinkler protection is extended to the balcony areas. In all cases, the use of untreated wood is permitted for pickets, rails, and similar guard elements when limited to a height of 42 inches (1,067 mm).

Section 1407 Metal Composite Materials

Metal composite materials (MCM) consist of a thin, extruded plastic core encapsulated within metal facings. As the use of MCM continues to increase, it is important to provide detailed requirements addressing this unique building element. Many of the provisions are based on requirements from elsewhere in this chapter and Chapter 26. Although having some of the same characteristics as foam-plastic insulation, light-transmitting plastic, plastic veneer, and combustible construction, MCM used as exterior wall coverings are specifically regulated by this section.

Where installed on exterior walls of buildings, MCM systems are regulated for surface-burning characteristics. In buildings of other than Type V construction, the flame-spread index cannot exceed 75 and the smoke-developed index is limited to 450. In such buildings required to have noncombustible exterior walls, the use of a thermal barrier is necessary to separate the MCM from the interior of the building unless specifically approved by appropriate testing. Alternatively, the installation of MCM to a limited height in compliance with Section 1407.11 modifies the general requirements.

Section 1408 Exterior Insulation and Finish Systems (EIFS)

Exterior Insulation and Finish Systems (EIFS) are non-load-bearing exterior wall coverings that are used extensively throughout North America, Europe, and the Pacific Rim. The provisions of Section 1408 are primarily intended to reference the applicable ASTM standards that are specific to EIFS. Reference is made to E 2273 Standard Test Method for Determining the Drainage Efficiency of Exterior Insulation and Finish Systems (EIFS) Clad Wall Assemblies, E 2568 Standard Specification for PB Exterior Insulation and Finish Systems (EIFS), and E 2570 Standard Test Method for Evaluating Water-Resistive Barrier (WRB) Coatings Used Under Exterior Insulation and Finish Systems (EIFS) for EIFS with Drainage. In addition to the several ASTM standards previously identified, reference is also made to various provisions found elsewhere in the IBC that are applicable to EIFS. Current ICC ES Acceptance Criteria further establish requirements for EIFS and related components, and numerous EIFS manufacturers hold evaluation reports to demonstrate code compliance.