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14
Exterior Walls

Chapter 14 establishes requirements for exterior walls. It also sets standards for wall materials and wall coverings, as well as for wall components such as windows, doors, and trim. The provisions of this chapter are meant to apply primarily to weather protection and moisture control. The definition of “exterior wall“ specifically excludes fire walls, which have additional fire-resistive requirements.

It is the intent of the code that exterior-wall requirements for weather protection and moisture control not supersede or compromise the overriding structural bearing and fire-resistance requirements for walls. On the other hand, the code does not intend for fire walls or structural bearing walls not to provide the required degree of weather resistance. As we will see as we proceed through the chapter, the intent is that weather resistance be built into exterior wall systems and that bearing walls need not have added envelope protection if they are designed as both load-bearing and weather-resistant systems.

Exterior-Wall Envelope

§ 1402.2 requires an “exterior wall envelope” to protect the structural members of a building, including framing and sheathing materials, as well as conditioned interior spaces from detrimental effects of the exterior environment.

Performance Requirements

§ 1402 sets out the performance criteria for exterior walls, wall coverings, and components.

Weather Protection

§ 1402.2 states that the basic performance criterion for exterior walls is providing an exterior-wall envelope that is weather-resistant. Exterior-wall systems must therefore be designed to prevent water penetration and the accumulation of water behind exterior veneers, and to provide drainage for any moisture that does enter the wall assemblies to the exterior of the veneer. The systems must also protect against condensation inside wall assemblies as required by § 1405.4, which describes flashing requirements.

Exception 1: Weather-resistant systems are not required when exterior concrete walls or exterior masonry walls are designed for weather resistance per Chapters 19 and 21, respectively.
Exception 2: Drainage requirements for wall assemblies (§ 1403.2 for water-resistive barriers and § 1404.4 for flashing) may be waived when acceptable testing is performed on envelope assemblies including joints, penetrations, and intersections per the test procedures of ASTM E-331. The basic criteria for this test require that a 4' ×' (1219 × 2438) wall section be tested. The test section must contain a typical opening control joint, wall/eave intersection, control joint, and wall sill. The test must simulate pressure differentials of 6.24 psf (0.297 kN/m²) and last for at least 2 hours. These criteria are established to require that the tested wall assembly with all of its typical parts be exposed to simulations of wind-driven rain conditions that can be reasonably anticipated in actual installations.
Exception 3: Exterior insulation and finish systems (EIFS) that comply with the drainage requirements of § 1408.4.1.

Other Requirements

Exterior walls are to be designed to resist structural loads per Chapter 16, and meet the applicable fire-resistance and opening-protection requirements of Chapter 7. In flood-hazard areas, designated per § 1612.3, exterior walls extending below the design flood elevation are to be resistant to water damage. Any wood used in these areas is to be pressure-treated or naturally decay resistant.

Figure depicts the water-resistive barrier.

Wall Materials

§ 1402 and § 1403 require that all materials used in exterior walls are to meet the structural criteria contained in Chapter 16, as well as the detailed provisions for specific materials contained in Chapters 19 through 26.

Concrete: Chapter 19
Aluminum: Chapter 20. Aluminum siding must satisfy the requirements of AAMA 1402.
Masonry and Glass Unit Masonry: Chapter 21
Steel: Chapter 22
Wood: Chapter 23
Glass: Chapter 24
Gypsum Board and Plaster: Chapter 25
Plastics: Chapter 26
Vinyl siding must conform to the requirements of ASTM D 3679.
Fiber-cement siding is to comply with ASTM C1186, Type A.
Exterior Insulation and Finish Systems (EIFS) are to comply with § 1407.

Installation of Wall Coverings

Vapor Retarders

§ 1404.3 describes the requirements for vapor retarders that are required in buildings to prevent the condensation of moisture inside of wall cavities. Moisture tends to migrate from the warmer and more moist interior of a building toward the exterior. If moisture is allowed to collect in wall cavities, it can lead to mold, mildew, or decay of the materials. The code requires different classes of vapor retarders, based on the location of the building in relation to the Climate Zones described in the International Energy Conservation Code (IECC).

Vapor retarder class is determined by the manufacturer's certified testing of assemblies. Certain materials, as described at right, are deemed by the code to meet the classes noted. The lowest class of vapor retarders is paint, which is Class III. This lowest level of vapor retarder is permitted in a specific group of assemblies in the Climate Zones listed in Table 1404.3.2.

Vapor retarders are classified based on manufacturers' tests. The following are classified in the code:

Figure depicts class I, II, and III types vapor retarders.

Per § 1404.3.1, Class I or II vapor retarders are to be installed on the interior side of frame walls in Climate Zones 5, 6, 7, 8, and Marine 4.
Class I and II vapor retarders are NOT to be provided on the interior side of frame walls in Zones 1 and 2. Class I vapor retarders are NOT to be provided on the interior side of frame walls in Zones 3 and 4. These are warmer climate zones.
The appropriate zone is to be selected in accordance with Chapter 3 of the International Energy Conservation Code.
Exceptions:
1. Basements
2. Construction where moisture or its freezing will not damage the materials
3. Conditions where Class III vapor retarders are required in § 1404.3.2
Class III vapor retarders (paint) are allowed if the conditions in Table 1404.3.2 are met.
Example for Climate Zone 5:

Flashing

§1404.4 requires the installation of flashing to prevent moisture from entering at locations such as those illustrated to the right. The intent of the list that contains examples, not just the conditions to be satisfied, is that flashing be provided at any condition where it would prevent moisture from entering the structure.

Wood Veneers

§ 1404.5 prescribes the requirements for installing wood veneers.

Notwithstanding the requirements of Table 1404.2 for the minimum thickness of weather coverings, wood veneer used in Type I, II, III, and IV construction is to be of thickness called out in § 1404.5.

The extent of wood veneer in other than Type V construction is also limited. The requirements are not exceptions, and all must be met for wood veneer to be used in these types of construction. The requirements are:

Anchored Masonry Veneer

§ 1404.6 prescribes specific requirements for the use of anchored veneers, whether of masonry, stone, or terra-cotta. These provisions apply to materials anchored to backing materials using mechanical fasteners. This is distinct from adhered veneers that are attached to the backing by adhesives. These requirements are broken down by material into separate sections.

§ 1404.6 also requires anchored masonry veneers to comply with the standards contained in § 12.1 and § 12.2 of TMS 402, but the text applies these requirements to several types of veneers: masonry, stone, slab-type, and terra-cotta.

Stone Veneer

§ 1404.7 requires stone veneer units up to 10'' (254) thick to be anchored to masonry, stone, or wood construction by any one of the following methods. The methods are based on the structural system backing the veneer.

With concrete or masonry backing, anchor ties of dimension and spacing as indicated on the illustration are to be provided. These ties are to be laid in mortar joints and are to be located in such a manner that no more than 2 sf (0.2 m²) of the wall is unsupported by the backing. In addition to the anchor ties in mortar joints attached to the backing with mechanical fasteners, there is to be a minimum of 1'' (25.4) of continuous grout between the backing and the stone veneer.
With stud backing, wire mesh and building paper are to be applied and nailed as indicated on the illustration. Anchors similar to those required at concrete or masonry backing are to installed in the mortar joints and anchored to the backing to support every 2 sf (0.2 m²) of veneer. Here too a minimum of 1'' (25.4) of grout is to fill the cavity between the backing and the stone veneer.

Figure depicts the vertical section of stone veneer.

Figure depicts the horizontal section of stone veneer.

Slab-Type Veneer

§ 1404.8 covers marble, travertine, granite, and other stone veneer units in slab form. These units are to be not more than 2'' (51) in thickness and are to be anchored directly to concrete or masonry backings, or to wood or metal studs. Dowels are to be placed in the middle third of the slab thickness, a maximum of 24'' (610) apart with a minimum of four per unit. The slab units are to be no larger than 20 sf (1.9 m²) in area. They are to have wire ties to the backing materials of size and spacing to resist a force in tension or compression of two times the weight of the attached veneer.

Terra-cotta

§ 1404.9 specifies anchoring terra-cotta veneers in a manner similar to that for slab veneers. The terra-cotta must be at least 1.625'' (41) in thickness with projecting dovetail webs on 8'' (203) centers. Metal anchors are to be placed at 12'' to 18'' (305 to 457) spacing in the joints between units and tied to the backing materials by pencil rods passing through loops in the wire ties and embedded in at least 2'' (51) of grout.

Adhered Masonry Veneer

§ 1404.10 considers adhered masonry veneer units to be held to the backing by the adhesion of bonding materials to the substrate. Exterior veneer is to comply with the applicable portions of § 12.1 and § 12.2 of the reference standard: TMS 402.

Exterior Veneers

Water-resistive barriers shall be installed as required in § 2510.6.

There is to be flashing at the foundation, using a corrosion-resistant screed or flashing of a minimum dimension. The water-resistive barrier is to lap over the exterior of the attachment flange of the screed or flashing.

Interior Veneers

§ 1404.10.3 applies only to the installation of interior adhered masonry veneers, which must comply with the same installation requirements and weigh no more than 20 pounds per square foot (0.958 kg/m2). Where supported by wood framing, the supporting members are limited to deflection to 1/600 of the span of the supporting members.

Metal Veneers

§ 1404.11 states that metal veneers must be of noncorrosive materials or must be coated with anticorrosive coatings such as porcelain enamel. Connections to the backing are to be made with corrosion-resistant fasteners. Wood supports for metal veneers are to be of pressure-treated wood. Joints are to be caulked or sealed to prevent penetration of moisture. Masonry backing is not required for metal veneers except as may be necessary for fire resistance per other code sections.

Metal-veneer walls need to be grounded for lightning and electrical discharge protection per Chapter 27 of the IBC and per NFPA 70.

Glass Veneers

§ 1404.12 permits glass panels to be used as thin exterior structural glass veneer. The pieces of such glass, used as finish and not as glazing, may not exceed 10 sf (0.93 m²) in areas up to 15' (4572) above grade and may not be larger than 6 sf (0.56 m²) above that height. The glass is to be bonded to the substrate with a bond coat material that effectively seals the backing surface. Over this, mastic cement is to be applied to at least 50% of the glass surface to adhere it directly to the backing.

Where the glass veneer is installed at sidewalk level, it is to be held above the adjacent paving by at least ¼'' (6.4) and the joint thus created is to be sealed and made watertight. When located more than 36'' (914) above grade, glass units are to be supported with shelf angles. When installed at a height above 12' (3658), the glass units are to be fastened at each vertical and horizontal edge in addition to the required adhesive mastic and shelf angles. Edges of the glass panels are to be ground square and are to be flashed at exposed edges.

Vinyl Siding

Per § 1404.14, vinyl siding is to conform with that section and with ASTM D 3679. It is permitted for use on exterior walls where the wind speed does not exceed 100 mph (45 m/s) and the building height does not exceed 40' (12 192) in Exposure C (see § 1609.3.1). Where buildings exceed these requirements, calculations or test data demonstrating compliance must be submitted. The siding is to be applied per the requirements of § 1404.14.1. The siding must meet the water-resistive barrier requirements of § 1402.

Fiber-Cement Siding

Fiber-cement siding is permitted per § 1404.16 on any type of construction. It is to meet the water-resistive barrier requirements of § 1402. The siding is to be applied per the manufacturer's instructions with fastenings per § 1404.16.

Polypropylene Siding

Per § 1404.18 use of polypropylene siding is to be limited to exterior walls of Type VB construction located in areas where the wind speed does not exceed 100 miles per hour (45 m/s) and the building height is less than or equal to 40' (12 192) in Exposure C. For construction located in areas where the basic wind speed exceeds 100 miles per hour (45 m/s), or building heights are in excess of 40' (12 192), tests or calculations indicating compliance with Chapter 16 shall be submitted.

Combustible Materials on the Exterior Side of Exterior Walls

§ 1405 applies not only to building materials but also to appendages that project beyond the plane of the exterior wall. Such appendages include balconies, bay windows, and oriel windows. The criteria for plastics in this application are contained in Chapter 26. The standards for ignition resistance of exterior materials are set forth in NFPA 268. Note, however, that the exceptions to § 1405.1.1.1 cover such broad areas that the criteria from NFPA 268 may not apply in many cases. The exceptions include: wood or wood-based products, combustible materials other than vinyl siding, and aluminum at least 0.019'' (0.48) thick and at exterior walls of Type V construction. Thus these requirements apply to classes of construction other than Type V.

Table 1405.1.1.2 shows the relationship of combustible veneers to fire-separation distance from a lot line. When located closer than 5' (1524) to a lot line, materials (those not covered by the exceptions) shall not exhibit sustained flaming per NFPA 268. As the distance to the lot line increases, the radiant-heat energy flux decreases. Thus the heat impact on the materials decreases with distance and the types of material that will not exhibit sustained flaming increases.

Combustible Materials in Construction Types I, II, III, and IV

Per § 1405.1.1, exterior wall coverings may be of wood where permitted by § 1404.5 in buildings of Types I, II, III, and IV construction if the buildings are no more than three stories or 40' (12 192) in height. Where such buildings have a fire-separation distance of less than 5' (1524), no more than 10% of the exterior wall may be of combustible materials unless of fire-retardant-treated wood. Where such exterior wall coverings are located more than 40' (12 192) above grade they must be of noncombustible materials and attached with noncombustible fasteners. Note that combustible exterior wall coverings constructed of fire-retardant-treated wood are permitted up to 60' (18 288) in height above grade plane regardless of the fire separation distance.

Fire-Blocking

When combustible wall coverings are furred from the wall and form a solid surface, § 1405.1.3 requires the space between the back of the covering and the wall to not exceed 1⅝'' (41), and the space must be fire-blocked per § 718 so that no open space exceeds 100 sf (9.3 m²). Note that Item 3 of § 1404.5 allows open or spaced veneers to project up to 24'' (610) from the backing wall. Fire-blocking may be omitted in certain circumstances, but good practice should dictate its inclusion in almost every condition where feasible.

Metal Composite Materials

Metal composite materials (MCM) are a recently developed type of exterior finish material combining metal skin panels with plastic cores. These materials are regulated in two ways, both as exterior finishes under § 1406 and as plastics under Chapter 26. They are required to meet all of the water-resistance and durability criteria set forth in this chapter for other finish materials. Their installation in rated construction is controlled by testing and approval data establishing flame spread and smoke generation. A gypsum wall board thermal barrier may be required under the assemblies to limit heat transfer from exterior fire exposure into the building. This barrier is not required when test data support its removal.

The use of this material will be governed by tests and approvals for individual materials. These tests and approvals must be examined in light of the detailed requirements for generic types of exterior enclosure. As new materials are tested and approved, they must be compared to the code requirements to determine detailed responses to their installation. An example of a typical exterior MCM assembly is illustrated. Note that per § 1406.11.3, installations of MCM may go up to 75' (22 860) in height if the installation meets a more stringent list of criteria in this section. Note also that per the Exception to this section, buildings with automatic sprinkler systems are exempt from the height limitation.

Successful installations of innovative materials such as MCM will be dependent on close conformance with manufacturers' recommendations. This is true of other innovations as well. The code endeavors to incorporate new materials and new ways of assembling familiar materials such as the composite of aluminum and plastics to create MCMs. Innovations usually precede code development, so such innovative materials must be incorporated into buildings using manufacturers' data in concert with close consultation with the AHJ.

Exterior Insulation and Finish Systems

Exterior insulation and finish (EIFS) systems are to conform to the requirements of § 1407. They are to be designed to comply with ASTM E 2568, conform to the structural requirements of Chapter 16, and meet the weather resistance requirements of § 1402. Installation is to be in accordance with the EIFS manufacturer's instructions.

Figure depicts finish coat, second coat, reinforcing mesh, base coat, insulation board, adhesive, sheathing, bottom track.

High-Pressure Laminate Systems

§ 1408 High-Pressure Decorative Exterior-Grade Laminates (HPL)

These exterior wall covering systems use panels made of layers of cellulose fibrous material impregnated with thermosetting resins and bonded together by a high-pressure process to form a homogeneous, nonporous core suitable for exterior use. They are usually applied as panels over a metal-channel backing system. These are often used in “rain screen” systems.

Per §1408.8, where HPL systems are used on exterior walls required to have a fire-resistance rating, evidence is to be submitted to the building official that the required fire-resistance rating is maintained.

Per the Exception, this requirement does not apply to HPL systems that do not contain foam plastic insulation and are installed on the outer surface of a fire-resistance-rated exterior wall in a manner such that the attachments do not penetrate through the entire exterior wall assembly.

§ 1409 Plastic Composite Decking