Fire-Resistant Wall Assemblies

    Scope Images
    Image
    The combustible siding product on the left side in this demonstration burns readily when exposed to a burning wood sample, while the noncombustible siding on the right does not ignite
    Scope

    In wildfire-prone areas, construct the wall assemblies, including the insulation, framing, and cladding, to be wildfire resilient by providing the following:

    • Design and construct wall assemblies that either do not require ventilation behind the cladding or utilize minimum back-ventilation air flow
    • Provide 1/16-inch metal screening at the bottoms and tops of the gaps that resist entry of airborne embers and pests.
    • Use non-combustible cladding, like stucco, fiber cement, brick, stone, or metal siding.
    • Use fire-retardant or fire-resistant sheathing, like non-paper-faced exterior gypsum or treated plywood.
    • Use fire-retardant framing.
    • Use fire-retardant or fire-resistant cavity insulation, like mineral wool, fiberglass, or cellulose.
    • Use a non-combustible interior lining, like drywall.
    • If continuous exterior rigid insulation is used, minimize the risk of combustion by
      • using a noncombustible rigid insulation like mineral wool or unfaced fiberglass,
      • or by minimizing or eliminating the air gap behind the cladding,
      • or, if the air gap will be ≥ 1 inch,
        • both the cladding and the exterior rigid insulation should be non-combustible
        • or the cladding should be non-combustible and combustible continuous insulation should be protected by a non-combustible layer.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

    Description

    Wall assemblies perform many important roles. They function structurally to hold up the building and they provide environmental separation, i.e., the wall assembly separates the indoors from the outdoors in terms of moisture, temperature, and weather through the use of various materials that provide the building envelope’s rain, air, vapor, and thermal control layers. If made very structurally sound, providing a continuous load path from roof to foundation, the walls can help a home withstand earthquakes, hurricanes, high winds, and tornadoes. If made with moisture-resistant materials and practices, they can help resist flooding, rain, and snow.

    If wall assemblies are made from noncombustible materials or fire-retardant-treated materials or constructed as fire-resistant assemblies, they can help protect the occupants and their property from wildfires (Figure 1 and Figure 2).

    Materials

    Some definitions of fire-related building material terms are provided below (MN SFM 2016):

    • Non-combustible materials will not ignite, burn or release flammable vapors when exposed to fire or heat; most non-combustible materials have a Class A flame spread rating.
    • Fire-resistant or fire resistance-rated refers to the rating of a building’s floor, wall, and ceiling assemblies’ ability to contain a fire inside that compartment and prevent it from spreading for a period of time, for example, a two-hour fire resistance-rated wall or a 20-minute fire-rated door.
    • Fire retardant or fire retardant-treated refers to chemicals, coatings, and treatments used to make combustible building materials like plywood or lumber resistant to decomposition when exposed to fire. Fire-retardant treatment is accomplished in a factory setting; there are no after-market products that can give lumber a “fire retardant-treated” listing. The addition of fire-retardant materials does not make an item non-combustible.
    • Flame spread rating (or flame spread index) refers to how fire spreads across a material’s surface. It is used to provide a Class A, B, or C flame spread rating on materials used on walls or ceilings. Chemicals can be applied that will reduce the flame spread rating of a material.
    • Fireproof is an old, outdated term intended to denote that something would not burn. Unfortunately, history has shown that many so-called “fireproof” buildings have burned so this term has fallen out of favor. The building construction materials themselves are rarely the first items to burn. The initial fire ignition usually involves combustible materials like trees, wood decks, or vegetative debris collecting in gutters or corners or inside from flammable contents that catch fire due to sparks entering through vents or open or broken windows (MN SFM 2016).

    For code definitions of noncombustible, ignition resistant, and fire resistant, see the Compliance tab. For a good explanation of the terms fire-resistant, ignition-resistant, noncombustible, and fire-retardant-treated materials and the tests used to define them, see the article Fire Ratings for Construction Materials by Stephen Quarles of the Insurance Institute for Business & Home Safety (Quarles 2019). The fact sheet Fire Code Terminology Related Fire Tests (MN SFM 2016) also provides helpful explanations of fire-related terms and tests.

    Researchers at the Insurance Institute for Business & Home Safety Research Center exposed two homes to flying embers and high winds - the home with wood siding and a wood door went up in flames, the home with fiber cement siding and a metal door suffered little damage.
    Figure 1.  Researchers at the Insurance Institute for Business & Home Safety Research Center exposed two homes to flying embers and high winds - the home with wood siding and a wood door went up in flames, the home with fiber cement siding and a metal door suffered little damage (Source: IBHS 2021).

     

    Make the right choices to make a home’s exterior more resistant to wildfire.
    Figure 2. Make the right choices to make a home’s exterior more resistant to wildfire with these recommendations based on research by the Insurance Institute for Business and Home Safety (Source: IBHS 2021).

     

    The most common residential wall assemblies are wood framed. Wood can be treated to be fire retardant. Fire-retardant or fire-resistant cavity insulation, sheathing, and continuous exterior insulation can be used. Non-combustible exterior cladding can be used (see Figure 3). Non-combustible interior lining can be used. Examples of non-combustible materials or fire-resistant materials include the following:

    • Non-combustible sidings include brick, stone, stucco, fiber cement, and most metal sidings.
    • Fire-retardant or fire-resistant sheathings include non-paper-faced exterior gypsum or fire-retardant-treated plywood (see Figure 4).
    • Noncombustible furring strips include metal hat channel.
    • Fire-retardant or fire-resistant rigid insulation products include mineral wool, fiberglass, and phenolic foam.
    • Fire-retardant or fire-resistant cavity insulations include mineral wool, fiberglass, or cellulose.
    • Noncombustible interior linings include drywall.
    • As an alternative to wood framing, homes could be constructed of noncombustible framing materials such as poured concrete, concrete masonry units, masonry brick, or steel framing.
    The combustible siding product on the left side in this demonstration burns readily when exposed to a burning wood sample, while the noncombustible siding on the right did not ignite.
    Figure 3. The combustible siding product on the left side in this demonstration burns readily when exposed to a burning wood sample, while the noncombustible siding on the right did not ignite (Source: IBHS 2019).

     

    A wall assembly approved for use in the wildland-urban interface has 5/8-inch Type X gypsum installed exterior of the wood sheathing and an exterior covering or siding that has a 1-hour fire-resistance rating.
    Figure 4. A wall assembly approved for use in the wildland-urban interface has 5/8-inch Type X gypsum installed exterior of the wood sheathing and an exterior covering or siding that has a 1-hour fire-resistance rating (Source: FEMA P-737 2008).

     

    Table 1 shows relative resistance to fire and other natural disasters for several wall cladding materials. Table 2 shows flame spread ratings for several common wall building materials.

    Table 1. Common Siding Materials, Estimated Installation Costs, and Relative Resistance to Several Types of Disasters (PNNL 2021)

    Siding Material

    Rated based on high, medium, or low resistance to wildfire

    Price ($/sq. ft. installed)1

    Wind-Borne Debris/Hail Impact Resistance

    Fire Resistance

    Pest Resistance

    Flooding - Sustained Moisture Resistance2

    Earthquake -Seismic Resistance

    Metal

    Med-High

    High

    High

    High

    High

    High

    $10-25

    Solid Wood (cedar shingles, clapboards, tongue and groove)

    Med

    Med

    Low-Med

    High

    High

    Med

    $7.5-12.5

    Wood Panel (plywood, OSB, T1-11)

    Low-Med

    Med

    Low

    Low

    High

    Low

    $3.5-7.2

    Wood-Plastic Composite

    High

    Low

    High

    Med

    High

    Med

    $7.5-9.5

    Fiber Cement

    Med

    High

    High

    High

    Med

    Med

    $7-10

    Plastic (vinyl siding, uPVC)

    Low

    Low

    High

    High

    High

    Low

    $3.5-8.5

    Masonry (brick, stone)

    High

    High

    High

    High

    Low

    High

    $11.5-15.5

    Stucco (3 coat)

    Med

    High

    High

    Low-Med

    Low

    Med-High

    $8-15

    Exterior Insulation and Finish System (EFIS) (1-2 coat stucco)

    Low

    High

    High

    Low

    Low

    High

    $14

    1. Price ranges derived from several sources with sidingcost.org being a starting source. Prices subject to change depending on many factors including but not limited to market conditions, material availability, and home complexity.

    2. The term prolonged or sustained contact means at least 72 hours (FEMA Tech Bull.2 2008).

     

    Table 2. Flame Spread Classification and Ratings for Common Building Materials (adapted from Louisiana Office of State Fire Marshall 2021) 

    Flame-Spread Classifications and Ratings (from NFPA Life Safety Code, not for roofs)
    Class I (or A) 0 – 25 FSR, Class II (or B) 26 – 75 FSR, Class III (or C) 76 – 200 FSR

    Material/Species

    Flame Spread Rating

    Flame-Spread Class

    Brick

    0

    I

    Fiber-cement

    0

    I

    Inorganic reinforced cement board

    0

    I

    Plywood, Fire-retardant-treated

    0-25

    I

    Gypsum Wallboard

    10-15

    I

    Gypsum Sheathing

    15-20

    I

    Engelmann Spruce, Western Red Cedar, West Coast Hemlock

    55-73

    II

    Birch, Idaho white pine, Douglas Fir, Lodegepole Pine, Red or White Oak, Maple, Ponderosa Pine

    80-115

    III

    APA Wood Structural Panels (includes APA 303 Sidings, T1-11)

    76-200

    III

    Particle Board

    116-178

    III

    Plywood, Pine

    120-140

    III

    Plywood, Oak

    125-185

    III

    Oriented Strand Board (OSB)

    150

    III

    Fiberboard, Medium Density

    167

    III

    Hardboard/pressboard/Masonite

    <200

    III

     

    Rain Screen Wall Assemblies and Fire Risks

    To help walls perform their rainwater control function, the wall should include a rainscreen assembly behind the cladding. This consists of an air and drainage gap over a water control layer to allow any rainwater that does get behind the siding to freely drain down and out of the wall. The water control layer, also called a water resistant barrier (WRB), can consist of a mechanically attached membrane like building paper or house wrap, a fully adhered membrane, a fluid-applied coating, an OSB sheathing product with an adhered integral water control layer, or rigid insulation with sealed joints. The drainage gap can be maintained with corrugated house wrap; plastic mesh or dimpled plastic products; or plastic or wood furring strips or metal hat channel.

    Figure 5 shows a wall assembly with a non-combustible brick cladding, fire-retardant or fire-resistant continuous exterior insulation, fire-retardant or fire-resistant sheathing, fire-retardant framing, fire-retardant or fire-resistant cavity insulation and a non-combustible interior lining.  The brick or stone veneer is installed over a 1-inch drained and vented cavity. This cavity should not be vented into soffit assemblies. It should be capped at the top and vented near the top with weep holes similar to the weep holes used at the bottom of brick walls.

    Figure 6 shows a wall assembly with a non-combustible fiber cement cladding, fire retardant or fire-resistant continuous exterior insulation, fire-retardant or fire-resistant sheathing, fire-retardant framing, fire-retardant or fire-resistant cavity insulation, and a non-combustible interior lining. The fiber cement siding is installed over a ½-inch drained and vented cavity. This cavity should not be vented into soffit assemblies. It should be capped at the top. The air leakage typical for lap siding provides the necessary air change in the cavity to provide back-cladding ventilation.

    Figure 7, Figure 8, and Figure 9 show a complete building section connecting an unvented roof assembly constructed with fire-resistant and fire-retardant materials to a wall assembly and foundation assembly with similar materials.

    Wall assembly with non-combustible brick cladding and fire-resistant or retardant rigid insulation, sheathing, framing and cavity insulation.
    Figure 5.  Wall assembly with non-combustible brick cladding and fire-resistant or retardant rigid insulation, sheathing, framing and cavity insulation (Source: Courtesy of BSC).

     

    Use as figure caption for figure 6: Wall assembly with non-combustible fiber cement cladding, metal hat-channel furring for air gap and fire-resistant or retardant rigid insulation, sheathing, framing and cavity insulation.
    Figure 6.  Wall assembly with non-combustible fiber cement cladding, metal hat-channel furring for air gap and fire-resistant or retardant rigid insulation, sheathing, framing and cavity insulation (Source: Courtesy of BSC).

     

    Building section connecting an unvented roof assembly constructed with fire-resistant and fire-retardant materials to a wall assembly with similar materials.
    Figure 7.  Building section connecting an unvented roof assembly constructed with fire-resistant and fire-retardant materials to a wall assembly with similar materials (Source: Courtesy of BSC).

     

    Building section showing a vapor diffusion ridge port constructed with fire-resistant and fire-retardant materials.
    Figure 8. Building section showing a vapor diffusion ridge port constructed with fire-resistant and fire-retardant materials (Source: Courtesy of BSC).

     

    Building section connecting wall assembly constructed with fire-resistant and fire-retardant materials to a foundation assembly with similar materials.
    Figure 9.  Building section connecting wall assembly constructed with fire-resistant and fire-retardant materials to a foundation assembly with similar materials (Source: Courtesy of BSC). 

     

    The size of the gap necessary to provide drainage behind cladding as part of a vented cladding system can be as small as 1/32nd of an inch behind some lap siding or up to 1 inch or more behind masonry claddings like brick or stone veneer, which are sometimes referred to as reservoir claddings because of the amount of water they can hold. For moisture control, the key is to make this gap continuous.

    The greater the gap – the greater the potential airflow in the gap. This airflow can have both a positive and negative effect. The positive effect is that airflow can promote drying of the wall assembly and specifically the cladding. The negative effect is that the airflow increases the fire risk for vented wall claddings due to the possibility of pulling burning embers up into the wall assembly during a wildfire event. There are several ways to minimize this risk. The gap can be sized as small as possible or the wall can be designed with no gap.

    Where gaps are ¾ inch or less, the fire risk is minimal due to boundary layer friction of the two surfaces. Any sparks or burning embers entering a small air gap would be starved for oxygen and would quickly die out.

    Synthetic stucco assemblies such as exterior insulated foam systems (EIFS) pose a small fire risk as there is no gap between the thin exterior lamina and the extruded polystyrene (EPS) that the lamina is adhered or bonded to, even though EPS is combustible. Drainage is provided behind the EPS by the gap resulting from installing vertical beads of adhesive that attach the foam to the water control layer. This gap is approximately 1/8 inch.

    Numerous wall configurations that provide drainage in small gaps can be utilized (Figures 10-17). None of these assemblies need to be fire stopped since the drainage gaps are small.

    In areas at risk for wildfires, drainage gaps that are 1 inch or greater should be limited to assemblies where both the cladding and the continuous insulation are non-combustible (Figure 18) or where combustible continuous insulation is protected with a non-combustible layer (Figure 19).  Mineral wool and unfaced fiberglass insulation boards are examples of noncombustible, fire-blocking rigid continuous insulation. Non-combustible claddings include brick or stone veneers, traditional stucco, fiber-cement siding or panels, or metal siding or panels. In Figure 19, the entire wall assembly functions as an interrelated system. The 2021 International Wildland-Urban Interface Code (IWUIC) requires that the wall assembly “system” be a minimum “1-hour fire-resistance-rated” construction from the exterior (ASTM E119 or UL263).  This typically limits the thickness of the combustible rigid insulation to less than 2 inches.

    If a drainage gap (vented cladding) is used, 1/16-inch wire screening should be installed at the bottom and top of the vent cavities to prevent the entry of airborne embers/cinders. These screens will also keep insects and pests out of the drainage and ventilation gap (see Figure 20). It is important that ventilations gaps not provide a pathway for airborne embers/cinders to enter soffit assemblies and ultimately roof assemblies.  The 2021 International Wildland-Urban Interface Code (IWUIC) expressly prohibits soffit ventilation.

    Small spacer strips consisting of ¼-inch plastic strips provide a drainage gap behind wall cladding with a gap that is too small to pose a fire risk from embers entering the gap.
    Figure 10.  Small spacer strips consisting of 1/4-inch plastic strips provide a drainage gap behind wall cladding with a gap that is too small to pose a fire risk from embers entering the gap (Source: Courtesy of BSC).

     

    Stone cladding system with a drainage mat provides a small, vented gap (≤ ¾ inch), over a water-resistant barrier house wrap that has a perm rating of 10 to 20 perms so it can serve as a vapor throttle.
    Figure 11.  Stone cladding system with a drainage mat provides a small, vented gap (≤ 3/4 inch), over a water-resistant barrier house wrap that has a perm rating of 10 to 20 perms so it can serve as a vapor throttle (Source: Courtesy of BSC). 

     

    Stucco wall assembly with a drainage mat providing a small vented gap (experience has shown that ≤ 3/8 inch is effective), and a water-resistant barrier house wrap serving as a vapor throttle.
    Figure 12. Stucco wall assembly with a drainage mat provides a small vented gap (experience has shown that ≤ 3/8 inch is effective), and a water-resistant barrier house wrap serving as a vapor throttle (Source: Courtesy of BSC). 

     

    Continuous rigid insulation coupled with thin (1/4-inch) spacer strips that provide drainage behind the wall cladding without increasing the fire risk of the assembly.
    Figure 13. Continuous rigid insulation coupled with thin (1/4-inch) spacer strips that provide drainage behind the wall cladding without increasing the fire risk of the assembly (Source: Courtesy of BSC). 

     

    Drainage behind wood shingle cladding is provided by a 3/8-inch-thick drainage mat.
    Figure 14.  Drainage behind wood shingle cladding is provided by a 3/8-inch-thick drainage mat (Source: Courtesy of BSC). 

     

    Drainage behind stone cladding is provided by “grooved” rigid insulation coupled with a filter fabric.
    Figure 15.  Drainage behind stone cladding is provided by “grooved” rigid insulation coupled with a filter fabric (Source: Courtesy of BSC). 

     

    Drainage and back ventilation of wood cladding is provided by ¾ inch furring (1x4).
    Figure 16.  Drainage and back ventilation of wood cladding is provided by 3/4 inch furring (1x4) (Source: Courtesy of BSC). 

     

    Drainage and back ventilation of wood cladding is provided by ¾ inch furring.
    Figure 17.  Drainage and back ventilation of wood cladding is provided by 3/4 inch furring (Source: Courtesy of BSC). 

     

    Metal hat channel provides a drainage gap of 1 inch between fiber-cement siding and mineral wool continuous insulation.
    Figure 18.  Metal hat channel provides a drainage gap of 1 inch between fiber-cement siding and mineral wool continuous insulation (Source: Courtesy of BSC).

     

    The combustible rigid foam insulation is protected by a non-combustible layer of mineral wool insulation; a 7/8 inch “hat-channel” provides the ventilation and drainage gap.
    Figure 19. The combustible rigid foam insulation is protected by a non-combustible layer of mineral wool insulation; a 7/8 inch “hat-channel” provides the ventilation and drainage gap (Source: Courtesy of BSC).    

     

    The furring strips that provide a drainage gap behind the lap siding are wrapped with ≤ 1/8-inch screen at the top and bottom of the wall to keep out bugs and burning embers.
    Figure 20. The furring strips that provide a drainage gap behind the lap siding are wrapped with ≤ 1/8-inch screen at the top and bottom of the wall to keep out bugs and burning embers (Source: Courtesy of EPA).

     

     

    Ensuring Success

    Consult a licensed architect or engineer to develop the detailed approach for rainwater control and fire resistance – where fire resistance includes more robust wildfire resiliency. 

    Minimize drainage gaps and back ventilation of claddings.  Provide screens that resist airborne ember/cinder entry. 

    Use a non-combustible cladding, fire-retardant or fire-resistant continuous exterior insulation, fire-retardant or fire-resistant sheathing, fire-retardant framing, fire-retardant or fire-resistant cavity insulation and a non-combustible interior lining. 

    Climate

    The approaches to fire resistance described here work in all climates; however, the approaches to rainwater control are climate dependent. 

    If wall assemblies are made very structurally sound, providing a continuous load path from roof to foundation, they can help a home withstand earthquakes, hurricanes, high winds, and tornadoes. See for example the guide Continuous Load Path Provided with Connections from the Roof through the Wall to the Foundation.

    If made with moisture-resistant materials and practices, they can help resist flooding, rain, and snow. See the guide Moisture-, Impact-, Fire-, and Pest-Resistant Exterior Siding.

     

    CAD

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    ENERGY STAR Certified Homes, Version 3/3.1 (Rev. 09)

    ENERGY STAR Certified Homes requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009, 2012, 2015 or 2018 International Energy Conservation Code (IECC) with some alternatives and exceptions, and achieve Grade 1 installation per RESNET Standards (see Insulation Installation (RESNET Grade 1).  You must meet or exceed the locally mandated requirements. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
    Exhibit 1, Item 2) Ceiling, wall, floor, and slab insulation shall meet or exceed 2015 IECC levels and achieve Grade 1 installation, per RESNET standards.

     

    2009-2021 IECC and IRC Insulation Requirements Table

    The minimum insulation requirements for ceilings, walls, floors, and foundations in new homes, as listed in the 2009, 2012, 2015, 2018, and 2021 IECC and IRC, can be found in this table

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IECC

    Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

    Chapter 5 (in 2015, 2018, 2020). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.

     

    2009, 2012, 2015, 2018 and 2021 International Residential Code (IRC)

    R301.2.1 Wind design criteria. Buildings shall be constructed in accordance with the wind provisions of this code using the ultimate design wind speed in Table R301.2(1) as determined from Figure R301.2(5)A. Where not otherwise specified, the wind loads listed in Table R301.2(2) adjusted f height and exposure using Table R301.2(3) shall be used to determine design load performance requirements.

    R602.1.2 (602.1.1 in 2012 IRC) End-jointed lumber. Approved end-jointed lumber identified by a grade mark conforming to Section R602.1 shall be permitted to be used interchangeably with solid-sawn members of the same species and grade. End-jointed lumber used in an assembly required elsewhere in this code to have a fire-resistance rating shall have the designation “Heat Resistant Adhesive” or “HRA” included in its grade mark (Note: IRC 2009 does not include language on fire-resistance or heat resistant adhesive).

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IRC

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

     

    2021 International Building Code (IBC)

    2303.2. Fire-retardant wood should have a flame spread index of 25 or less when tested in accordance with ASTM E84 or UL 723.

     

    2009, 2012, 2015, 2018 & 2021 International Wildland-Urban Interface Code (IWUIC)

    Section 202. Definitions.

    Ignition-resistant building material is a material that resists ignition or sustained flaming combustion sufficiently so as to reduce losses from wildland-urban interface conflagrations under worst-case weather and fuel conditions with wildfire exposure of burning embers and small flames. The material should exhibit a flame spread index of 25 or less as specified in the 2021 IWUIC, Section 503.2.

    Non-combustible is a material that will not ignite and burn and is conforming to ASTM E 136.

    Section 503.2 Ignition-Resistant Building Material. This section outlines compliance pathways for ignition-resistant building materials:

    1. The material can be tested using ASTM E84 or ASTM E2768 (see code for additional requirements including flame spread, flame front, weathering, and identification)
    2. Noncombustible material which is defined in IWUIC Section 202.
    3. Fire-retardant-treated wood as per section 2303.2 of the International Building Code.

    Section 504.5 for Class 1 Ignition-resistant construction and 505.5 for Class 2 Ignition-resistant construction. Exterior walls. Exterior of buildings or structures shall be constructed with either, materials approved for not less than 1-hour fire-resistance-rated construction on the exterior side, approved noncombustible materials, heavy timber or log wall construction, fire-retardant-treated wood on the exterior side which is labeled for exterior use and meets the requirements of IBC Section 2303.2, or ignition-resistant materials complying with Section 503.2 on the exterior side (note: for Class 2 Ignition-resistant construction, ignition-resistant materials on the exterior side does not need to comply with Section 503.2).

    Note: Class 2 ignition-resistant materials on the exterior side do not need to comply with Section 503.2. In IWUIC 2009-2015 Class 1 ignition-resistant materials on the exterior side also did not have to comply with Section 503.2.

     

    National Fire Protection Association (NFPA) 1144 Standard for Reducing Structure Ignition Hazards from Wildland Fire

    The National Fire Protection Association (NFPA) uses the following definitions for combustible, noncombustible, and ignition-resistant material (NFPA 1144 -2018).

    Combustible – Any material that, in the form in which it is used and under the conditions anticipated, will ignite and burn or will add appreciable heat to an ambient fire.

    Noncombustible – Noncombustible building materials shall be materials that comply with any one of the following:

    1. The building material, in the form in which it is used, and under the conditions anticipated, will not ignite, burn, support combustion, or release combustible vapors when subjected to fire or heat.
    2. The building material is reported as passing ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C.
    3. The building material is reported as complying with the pass/fail criteria of ASTM E136 when tested in accordance with the test method and procedure in AST E2652, Standard Test Method for Behavior of Materials in a Tube Furnace with a Cone-Shaped Airflow Stabilizers at 750°C.

    Ignition-Resistant Material – A type of building material that resists ignition or sustained flaming combustion. Ignition-resistant building materials shall maintain their fire performance and their mechanical performance under conditions of use. Materials shall be tested on all sides with the extended ASTM E84 test, Standard Test Method for Surface Burning Characteristics of Building Materials (UL 723). Material shall exhibit a flame spread index not exceeding 25 and shall not show evidence of progressive combustion following the extended 30-minute test. Material shall exhibit a flame front that does not progress more than 10.5 feet beyond the centerline of the burner at any time during the extended 30-minute test.

    Section 5.6 Exterior Vertical Walls.
    5.6.1 Exterior vertical wall coverings shall meet the requirements for an ignition-resistant material, exterior fire-retardant-treated wood, noncombustible material, or be an exterior wall assembly exhibiting a minimum 1-hour fire resistance rating when tested in accordance with ASTM E119, Standard Test Methods for Five Tests of Building Construction and Materials, and exhibiting a minimum Class B flame spread index, when tested in accordance with ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, where walls are potentially exposed to a wildland fire, unless the Authority Having Jurisdiction (AHJ) determines that the wildland fire risk and structure assessment requires greater protection.

    5.6.2 All exterior walls shall be protected with 2 inches (50 mm) nominal solid blocking between exposed rafters at all roof overhangs, under the exterior wall covering on all sides exposed to native vegetation as determined by the (AHJ).

    5.6.3 When appendages and projects are attached to exterior walls required to exhibit a fire resistance rating, they shall be constructed to maintain the fire resistance rating of the wall.

    5.6.4 A minimum of 6 inches (150 mm) noncombustible vertical separation between a horizontal surface and siding shall be maintained.

    This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

    Existing Homes

    When renovating a home in a high wildfire risk area, choose fire-resistant or noncombustible materials as described in this guide.

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    IBHS Fortified Home
    Organization(s)
    IBHS Fortified Home
    Publication Date
    Description
    Website describing the Insurance Institute for Business & Home Safety (IBHS)'s Fortified Home program which offers home builders standards and guidance for constructing and renovating homes for increased disaster resistance.
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Website providing the technical specifications and related documents for home builders, subcontractors, architects, and other housing professionals interested in certifying a home to the EPA's Indoor airPLUS program requirements.
    Author(s)
    Minnesota Department of Public Safety,
    State Fire Marshal Division
    Organization(s)
    MN SFM
    Publication Date
    Description
    Factsheet describing fire related terms such as noncombustible, fire resistant, fire retardant, flame spread, how they are applied, and related testing standards.
    Author(s)
    Quarles
    Organization(s)
    U.S. Department of Agriculture National Cooperative Extension
    Publication Date
    Description
    Article defining terms and testing requirements for fire-resistant construction materials including combustible, noncombustible, fire-resistant or fire-resistance, and ignition-resistant.
    Author(s)
    Insurance Institute for Business & Home Safety
    Organization(s)
    IBHS
    Publication Date
    Description
    Website describing wildfire related research conducted by the Insurance Institute for Business & Home Safety at the IBHS Research Center.
    Author(s)
    Insurance Institute for Business & Home Safety
    Organization(s)
    IBHS
    Publication Date
    Description
    Webpage describing ways builders and communities an reduce wildfire risk.
    Author(s)
    U.S. Department of Energy
    Organization(s)
    DOE
    Publication Date
    Description
    Website providing information on U.S. residential and commercial building codes including adoption status.
    Author(s)
    Lstiburek
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Report covering the fire performance of combustible cladding over combustible insulation.
    Author(s)
    Lstiburek
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Report covering reservoir claddings, back ventilation and vapor throttles.
    Author(s)
    Quarles
    Organization(s)
    Insurance Institute for Business & Home Safety
    Publication Date
    Description
    Report covering the migration of wind-blown embers in roof vents.
    Author(s)
    Lstiburek
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Report covering non-combustible continuous exterior insulation and non-combustible roof venting.
    Author(s)
    Louisiana Office of State Fire Marshall
    Organization(s)
    Louisiana Office of State Fire Marshall
    Publication Date
    Description
    Site showing flame spread ratings and definitions for common building materials.
    Author(s)
    Minnesota Department of Public Safety,
    State Fire Marshal Division
    Organization(s)
    MN SFM
    Publication Date
    Description
    Factsheet describing fire related terms such as noncombustible, fire resistant, fire retardant, flame spread, how they are applied, and related testing standards.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

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