Moisture-, Impact-, Fire-, and Pest-Resistant Exterior Siding

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    Moisture-resistant plastic and fiber cement exterior trim and cladding are indistinguishable from wood building elements.
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    Select the siding material that is best suited to withstand the hazards the home is likely to face in its lifetime.

    • Select siding materials that can resist likely hazards for the home’s locale such as impacts from hail and wind-borne debris, wildfire, pests, and moisture.
    • Install siding with the mindset that it will leak in its lifetime.
      • Provide drainage behind the cladding.
      • Flash windows, doors, and penetrations so they don’t depend on the siding to be waterproof.

    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

    The purpose of siding, in addition to being an aesthetically pleasing finish, is to shed rainwater and keep it from wetting more water-sensitive layers in the home’s wall assembly. Besides shedding rainwater, the second most important function of siding is to resist wind pressures. Other important functions of the siding are to protect the wall from ultra-violet light, insects, fire, hail, snow, and impacts from wind-driven debris, in addition to providing aesthetics to the home. Builders should select siding materials that are highly resistant to the hazards common to their locale.

    When selecting a siding product, builders and homeowners should keep in mind that not all siding products have undergone the same level of rigorous testing. There are hundreds of trademarked and proprietary siding products in the industry, each advertising its own unique characteristics. One should carefully evaluate the claims made by a product that uses a unique blend of materials and/or manufacturing methods to overcome the material weaknesses of its product family. Siding product manufacturers often put their products through an array of American Society for Testing and Materials (ASTM) tests; however, these tests don’t always discover flaws that only become apparent after years of real-world exposure. Thus, many builders, universities, national laboratories, and independent testing facilities conduct tests beyond the ASTM scope, including long-term exposure testing in mockup walls. Field studies, building science forensics, and real-world experience can offer insight into a product’s resilience over time. Some of this research is referenced in the More section of this guide.

    This guide explores the typical material properties of the main types of siding materials used in residential housing in the United States as they relate to resistance to the hazards imparted from moisture, impact from wind-driven debris and hail, fire, pests, floods, and earthquakes.

    For best results, always follow the manufacturer’s instructions for the specific brand and model of product you are using. Note that many siding products have an International Code Council (ICC) evaluation service report (ICC-ES or ESR) (found online by searching for “ESR” and the product name). The ESR spells out the basic installation requirements for the particular product and takes precedence over the code and the manufacturer’s published installation instructions where instructions differ. For example, see the ESR for information on fasteners and fastener patterns, flashing details, clearances to the ground and other edges, and treatment of cut edges and joints.  

    Table 1 below lists common siding materials and estimated installed costs for each siding type. It also provides a comparative rating of their resistance to hazards including rot, pest, fire, and impacts from wind-driven debris.

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

    Siding Material

    Rated based on high, medium, low

    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 range 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).

     

    Wind Resistance

    Exterior wall coverings can be blown off of a building, even during wind events with wind speeds below the design wind speed. All types of wall coverings including vinyl siding, brick veneer, fiber-cement siding, and wood and hardboard siding, can perform well in high winds if they are properly installed for high winds. Some tips for siding installation in high wind environments from the FEMA Home Builders Guide to Coastal Construction (FEMA-499 2010, Technical Fact Sheet 5.3, Siding Installation in High-Wind Regions). include the following:

    • Choose siding products that are rated for performance in coastal or high-wind environments.
    • Use well adhered or properly attached weather-resistant barriers such as a fluid-applied air barrier product, properly fastened house wrap that is overlapped shingle style and sealed at all seams with rollered tape, or taped rigid foam, to stop wind-driven rain that gets behind siding. Siding corners can be reinforced for further resistance to wind-driven rain (Figures 1 and 2).
    • Follow the manufacturer’s installation requirements for the wind speed rating or design pressure of the location.
    • For buildings located within 3,000 feet of the ocean shoreline, use stainless steel fasteners. In other locations, use corrosion-resistant galvanized or aluminum nails. Avoid using dissimilar metals together. See the Training tab for an example of a nailing schedule to increase the resistance of metal panel siding to high winds.
    • If installing vinyl siding in high-wind areas, use siding rated for high wind zones and install with fasteners per the manufacturer’s instructions. Products that have been rated for high winds typically have an enhanced nailing hem and thicker gauge vinyl. See Figure 3.
    • Install braced gable end walls with structural sheathing and no gable end vents, or retrofit existing gable end walls as described in the guide  Lateral Bracing in Gable End Walls.
    • Prime all six sides of wood, engineered wood, and fiber cement siding products and install all siding over a rain screen air gap to increase rot resistance.
    • Properly flash around doors and windows to keep out wind-driven rain as described in the guide Windows and Doors are Fully Flashed.
    Wood siding installation details to improve resistance to wind-driven rain at corners
    Figure 1. Wood siding installation details to improve resistance to wind-driven rain at corners (Source: FEMA P-499 2013).
    Use proper lapping of siding to keep water flowing down and out of walls.
    Figure 2. Use proper lapping of siding to keep water flowing down and out of walls (Source: FEMA P-499 2013).
    Features of standard and high-wind vinyl siding.
    Figure 3. Features of standard and high-wind vinyl siding (Source: FEMA P-499 2013). 

    Moisture Resistance

    Taking the right steps to improve the moisture resistance of the siding can greatly increase its durability and resistance to all types of natural disasters. Siding boards that have rotted around the fasteners are more likely to be pulled off by high winds. Boards that have buckled or cracked are more likely to catch embers in a wildfire. Damp wood attracts termites and carpenter ants.

    Rainscreens

    Regardless of the material, siding should not be thought of as a waterproof layer. Rather, it should be assumed that ALL siding, regardless of material type, will leak in its lifetime. Thus, it is paramount for a wall to have adequate backside drainage and drying to allow water and moisture that gets behind the siding to come back out. Drainage is provided by a gap or air space between the siding and a water control layer typically located on the exterior of the wall framing and sheathing.  The siding acts as a “screen” and the approach is sometimes referred to as a “rainscreen.”  The water control layer is often referred to as a “water resistive barrier” or WRB.  The gap or air space can be created by using furring strips (Figure 1), a drainage mat, or textured house wrap installed behind the wall cladding. This gap or air space can be ventilated with vent openings at the top and bottom  to promote air circulation. Locating vent openings only at the bottom of the wall provides drainage and some air exchange. The vent openings are covered with screen to keep out bugs and burning embers (Figure 1) (Straub 2009).

    For more information about improving the moisture resistance of wood siding, see the Building America Solution Center guide “Moisture-Resistant Wood- Based Cladding and Trim.”

     

    This wall assembly shows a drainage gap formed by installing furring strips over the building paper which serves as a weather-resistive barrier behind the wood or fiber cement lap siding
    Figure 4. This wall assembly shows a rain screen created by installing furring strips to form a gap between the siding and the building paper, which serves as a weather-resistive barrier (WRB). Drainage occurs in the gap or air space between the wood or fiber cement and the WRB (Source: Courtesy of EPA Indoor airPLUS).

     

    The minimum recommended size of the gap or air space depends on the siding material used. Siding or cladding materials that are porous and absorb water, often called reservoir claddings (for example, brick or stone veneer) need larger gaps or air spaces to dissipate or redistribute and control the absorbed water. The International Residential Code requires a minimum nominal 1-inch air space between the WRB that is typically installed over the sheathing and the brick veneer (IRC 2018 Table R703.8.4(1)). The IRC does not specify the spacing behind other siding types. For other siding materials the requirement is that the “exterior wall envelope be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water-resistance barrier behind the exterior veneer as required by Section 703.2 and a means of draining to the exterior water that enters the assembly” (IRC R703.1.1). A drainage gap of 1/4 inch is a recommended best practice behind stucco and 1/16 inch (about the thickness of some textured house wrap) is recommended behind lap siding (Baechler et al. 2011). This drainage gap also reduces moisture transport in the form of vapor drive, which occurs when rainwater is absorbed into the siding and then is driven into the wall by heat from the sun as it dries the wall. Less absorptive siding materials  require smaller sized gaps depending on the home’s location. The IRC requires Class I or II vapor retarders in exterior walls in Climates zones 5 through 8 and Marine 4 but permits the use of Class III vapor retarders (acrylic latex paint) if a vented cladding is used over plywood, OSB, fiberboard, or gypsum sheathing (IRC 2018 Table R702.7.1). In the Northwest, the above-code certification program Earth Advantage requires a 3/8-inch rainscreen under masonry siding but leaves the rainscreen as a points option for other siding types (Earth Advantage 2012). 

    The Building Enclosure Moisture Management Institute (BEMMI) recommends a rainscreen with a 3/16-inch minimum airspace be installed in any area receiving more than 20 inches of annual rainfall if using an absorptive (resevoir) cladding material. BEMMI recommends that areas receiving 40 inches or more of rainfall should utilize a rainscreen design regardless of cladding material. ASTM E2925-19 specifies that engineered rainscreen mesh, textured, and batten products provide at least a 3/16 inch gap. When specifying an engineered rainscreen product for masonry, it is important that the drainage mat have a filter fabric bonded to one side. This filter fabric keeps mortar from blocking air flow and provides obstructed channels for water to drain down and for ventilating air to flow through the air gap (Dagleish and Lolley 2016).

    Water and moisture that gets behind siding without an effective means of coming back out has been the cause of extensive damage to thousands of homes costing millions of dollars annually in repairs. Because of this, some building code jurisdictions have created a Rain Screen Acknowledgement Form to be signed by the builder to explicitly ensure the builder is aware of this need for wall drainage in an attempt to reduce the number of future water damage cases (City of Newberg 2010).

    While a rainscreen provides a great deal of water damage protection to a home’s shear wall sheathing and framing, it also has benefits for the siding. A rainscreen greatly enhances the drying rate of siding materials that absorb water. As a result, wood siding can dry quickly and therefore swell less when it gets wet. The reduced movement improves the longevity of the paints and stains. A moisture content below 20% also inhibits the growth of fungi, an important cause of wood rot. Wood siding that can dry quickly and minimize the time it is in a high moisture state will stave off decay much longer.

    A rainscreen is also beneficial in areas that experience high annual snow accumulation. The rainscreen gap separates the siding from the rest of the wall, allowing the siding to stay as cool as the outside temperature. This keeps snow from melting and thus helps keep the siding material dry. This is the same principle that helps a “cold” roof, one installed over a vented attic or above-deck venting, to have a cooler roof surface which helps to prevent the formation of ice dams by minimizing the thawing and freezing of snow on the roof. Even with a rainscreen, melting snow can cause localized areas of siding to experience prolonged periods of sustained moisture; thus, it is valuable to select a product that is rated highly for resisting sustained moisture contact.

    Siding Transition Details

    Regardless of the siding material, its ability to deflect rain water must be helped in vulnerable and critical areas such as the transitions from the roof to the walls, windows to siding, doors to siding, penetrations to siding, and exterior lighting to siding. Figure 5 shows an example of a kickout diverter which is a type of flashing used to divert water into the gutter from a roof section that abuts a wall section. The kickout prevents bulk water from streaming down or into the siding. Siding materials are designed to deflect precipitation, not a continuous stream of water. Siding most often fails at these transition and interface points where a flashing detail was poorly designed or omitted completely (Figure 6). Mistakes in these details often cause extensive damage and rot to the entire wall assembly from the siding to the sheathing, framing, insulation, and drywall (Parlee 2018).

    Kickout diverter flashing keeps bulk water from the roof from overflowing the gutter and continuously wetting the siding material.
    Figure 5. Kickout diverter flashing keeps bulk water from the roof from overflowing the gutter and continuously wetting the siding material (Source: Courtesy of Dryflekt).
    Missing step flashing and kickout flashing caused completely rotting away of the small piece of wall sheathing at this complicated roof juncture, as well as rotting of some of the roof sheathing, the fascia board, the framing member behind the fascia board and the plywood soffit cover below the eave
    Figure 6. Missing step flashing and kickout flashing caused rotting of wall and roof sheathing, fascia, framing, and plywood cover below the eave at this complicated roof juncture. (Source: Courtesy of PNNL).

     

    Impact Resistance

    The most common sources of impact damage are from hail and wind-borne debris from a hurricane or tornado. However, damage can also occur from a lawn mower, weed trimmer, or snowblower throwing up a rock. Siding options that perform well in impact tests include steel metal panels, fiber cement siding, wood composites, masonry and brick walls, and brick and stone veneer walls, provided the siding materials are installed over OSB or plywood sheathing (Peters and Robertson 2012; Bennett et al. 2005; Kashuba et al. 2001).

    Among metal siding options, steel panels perform better than aluminum panels, which are more prone to cracking when struck. This difference is important for climates that experience hailstorms. Wood composites perform better than fiber cement siding, which is more rigid, brittle, and prone to cracking when struck. Some vinyl siding products tend to crack and fracture when struck with a fast-moving object.

    Stucco and EIFS must be installed with a rainscreen for backside drainage, which means the force of a localized impact cannot be readily transmitted to the support structure. Due to the rigidity and brittleness of stucco and EIFS, once the strength of the cladding is exceeded, it will crack (Brown et al. 2004). Unlike brick and stone veneers, stucco and EIFS are not thick enough to resist and dissipate the energy of a large hail stone or test missile.

    In short, the siding materials that are most resistant to impact damage are either strong but also have enough flexural strength to resist cracking, chipping, and fracturing when struck with a high-speed object, or they are strong and have enough mass to dissipate the energy of an impact before cracking. A continuous drainage mat or rainscreen mat can provide more uniform continuous support to protect the siding against impacts than a furring strip rainscreen would provide.

    Note in high-velocity hurricane zones (HVHZ), even if the siding is resistant to impact damage, the home’s exterior walls should still be continuously sheathed with ≥ 19/32-inch plywood or tightly fitted diagonally placed ≥ 5/8-inch boards to help resist a concentrated load impact from hurricane-generated wind-borne debris (ICC FBC 2017 Section 2322.3).

    Fire Resistance

    As more homes are built in the wildland-urban interface (WUI), the potential costs and impacts of wildfires in these areas increases. To reduce the threat of wildfires, many communities are adopting building codes that require new homes constructed in the WUI zone to meet wildfire-resistance standards (Quarles and Pohl 2018). These codes typically require exterior walls to be

    • sheathed with Type X 5/8-inch gypsum over the wood sheathing and under the house wrap (Figure 7)
    • sided with an approved non-combustible material that is a listed 1-hour assembly or is listed on the local jurisdictions approved list of materials, for example the California Office of the State Fire Marshall (OSFM) list of approved materials (CA OSFM 2021)
    • or, constructed with heavy timber or log walls where any horizontal dimension is a minimum of 6 inches thick.
    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 7. 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 737 2008).

    The siding materials most likely to meet the 1-hour fire-resistance rating are stone, stone composites, fiber-cement, and metal. Wood can also be made to meet the 1-hour fire-resistance rating if it is treated with a fire-retardant chemical; however, these chemicals have limited lifespans and need to be reapplied. Vinyl and plastic composite sidings are typically not appropriate for homes constructed at a location with a high fire danger because the plastics melt at a relatively low temperature, see Figure 8.

    Some vinyl siding products will melt when exposed to high heat
    Figure 8. Some vinyl siding products will melt when exposed to high heat (Source: IBHS 2019).

    Another measure of the fire performance of a siding or sheathing material is its flame-spread rating. The best known test for developing this rating is the American Society for Testing and Materials (ASTM) Test Method E-84, “Standard Test Method for Surface Burning Characteristics of Building Materials,” commonly known as the tunnel test. The tunnel test measures how far and how fast flames spread across the surface of a sample of the material 20 inches wide and 25 feet long that is installed as the ceiling of a test chamber and exposed to a gas flame at one end. The most commonly used flame-spread classifications are Class I, II, and III or A, B, and C listed with their flame spread ratings (FSR) in Table 2. In general, inorganic materials such as brick or tile are Class I materials, whole wood products (“as sawn from the tree”) are usually Class II, while reconstituted wood materials such as plywood, particle board, or hardboard are Class III. Figure 9 shows a comparison of flammability in two siding products – a wood siding that is combustible and a fiber cement siding that is non-combustible. Table 2, which was compiled from various sources, shows flame-spread ratings for several common building materials (LA Office of State Fire Marshall 2021).

    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 9. 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).

    Table 2. Flame Spread Classification and Ratings for Common Building Materials (adapted from Louisiana Office of the 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

    Here are some ways to increase a home’s fire resistance related to siding:

    • Install non-combustible siding.
    • Construct the foundation to have at least 6 inches of noncombustible foundation siding between the ground and the first course of lap siding.
    • Install metal flashing between wood decks and siding.
    • Install metal drip edge to keep embers from getting lodged between the roofing and wood fascia boards.
    • Install horizontal soffit covers to keep embers from lodging in open and/or angled soffits and allowing exposed rafter tails to catch fire.
    • Instruct the homeowner to trim vegetation to keep branches 10 feet back from the house and to keep the roof cleared of debris at all roof-wall intersections.

    Rainscreen in High-Fire-Danger Locations

    There are concerns that the rainscreen cavity will provide a chase for a fire to spread rapidly up a building. These concerns are supported by examples from laboratory tests and post-fire investigation of buildings such as a museum in Norway where fire was found to have travelled via the rainscreen cavity (Rukavina et al. 2017, Jarnskjold et al. 2016). The cavity openings can be covered with metal screening ≤1/16-inch holes, which will keep out burning embers as well as bugs. There are also commercially available products from multiple manufacturers to control for this risk. The products are installed in the rainscreen cavity and contain a heat-activated expansion material that expands to close the rainscreen chase when it experiences the high heat of a fire, as shown in Figure 10. These products are commonly installed at the bottom and top of the rainscreen cavity and in between the floors of a multi-story building. The rainscreen would be installed in place of or between the house wrap and the exterior covering shown in Figure 10. Additionally, metal furring strips can be used in place of wood to minimize the combustible fuel in the wall assembly and they won’t melt like a plastic drainage mat would.

    Fire barriers for ventilated wall cavities use thermally activated expansive materials to close off the ventilation space between the wall cladding and the sheathing during a fire while allowing air flow through the metal mesh during normal conditions
    Figure 10. Fire barriers for ventilated wall cavities use thermally activated expansive materials to close off the ventilation space between the wall cladding and the sheathing during a fire while allowing air flow through the metal mesh during normal conditions (Source: Odice).

    Pest Resistance

    Termites and carpenter ants cause more than $2 billion in damage each year, more property damage than that caused by fires and windstorms combined (USFS 2014). A home’s termite risk is location dependent as shown in Figure 11. Thus, the importance of selecting a siding material that is termite resistant depends on the termite risk.

    Relative Risk of Subterranean Termite Infestation in the United States
    Figure 11. Relative Risk of Subterranean Termite Infestation in the United States (Source: USDA 2006).

    For homes located in a region of moderate, high, or very high termite risk, it is paramount to take this risk into consideration in siding material selection. Metal, stone, fiber cement, vinyl siding, and many wood composites sidings all perform well by not attracting termites. Cedar provides moderate protection against termites while other woods and wood panel sidings perform poorly at deterring termites.

    Although many siding options are quite good at deterring termites, it should be noted that termite deterrence requires a whole house systems approach to be successful. This includes providing adequate rainscreen or drainage to keep the wood framing and sheathing behind the siding dry (below 20% moisture content). The foundation design also plays a pivotal role in keeping siding, sheathing, and framing high enough above the finish grade so that they are less prone to wetting. Termite shields should be installed just above the foundation and termite inspection areas should be made visible at the top of interior basement walls. For more information about the different elements of a robust termite deterrent design, please see the Solution Center checklist on pest-resistant construction.

    Besides termites, pests such as bees and mice can get behind the siding into the rainscreen/drainage plane area of a wall to build hives or nests, as shown in Figure 12. The weep holes used to ventilate and drain the air cavities behind siding materials must be protected from pest entry through the use of screen covers. Use a screen mesh with small openings (1/55-inch or 0.5-mm) to protect against small pests as shown in Figure 13.

    Bees made a nest in the drainage plane behind a brick veneer wall by entering via unscreened weep holes
    Figure 12. Bees made a nest in the drainage plane behind a brick veneer wall by entering via unscreened weep holes (Source: Farber 2018).
    What mesh opening size is needed to keep out what type of pests?
    Figure 13. What mesh opening size is needed to keep out what type of pests? (Source: Courtesy of TERM Barriers by Polyguard Products). 

    Flooding and Extended High-Moisture Resistance

    Rainscreens allow water and moisture that gets behind the siding through seams, edges, and fastener penetrations to leave the wall assembly. However, in the event of a flood, the siding product could be underwater for days to weeks. Some siding materials are able to survive such long periods of high moisture contact without experiencing permanent degradation while other materials cannot. Homes that are in the flood plain must use FEMA Class 4 or Class 5 materials for the parts of the home that are below the flood elevation (FEMA Technical Bulletin 2, 2008). Class 4 and 5 materials are able to withstand being submerged for 72 hours without sustaining permanent damage and can be successfully cleaned after a flood to render them free of most harmful pollutants.

    For more information on constructing flood resistant walls and retrofitting walls after a flood see the Solution Center guides “Wash-and-Dry Wall Assemblies” and “Retrofitting Walls After a Flood.”

    Moving water during a flood subjects the siding to pressures from the current, thus thin and brittle materials such as stucco perform worse than thicker cement products such as fiber cement siding and brick veneers. Siding materials that meet the Class 4 and 5 FEMA rating are metal siding, stone, brick, fiber-cement, solid woods, and plastic (FEMA Technical Bulletin 2, 2008).

     

    Earthquake Resistance

    Siding materials that have higher levels of ductility combined with an installation that includes movement joints are the most adapted to surviving an earthquake and remaining functional afterwards. Brittle materials such as stucco and cement fiber products may become cracked during seismic events. A sufficiently stiff structural sheathing can be used behind these brittle siding finishes to minimize such damage (FEMA P-762 2009). For siding products that are installed in large sheets or panels, the ductility of the nail and nailed connections between the siding and the framing provides adequate ductility. Metal panels that are attached using metal cleats allow for more movement than those directly attached with screws (Sabino 2016).

    The residential code requires that the shear strength of the wall take into account the forces that high-mass siding finishes such as brick, brick veneer, and stone would impart onto the shear wall during an earthquake (IRC Table R602.10.6.5). Additionally, the residential code requires these high-mass siding finishes to be adequately connected to the structure to minimize the life-safety hazard they pose during an earthquake (IRC R703.8).

     

    Conclusion

    The primary function of siding is worth reiterating: it is to shed bulk water. If a siding material is failing and there is no effective rainscreen or drainage plane behind it, water will more than likely find a way into the interior components of a wall assembly, including the sheathing, framing, and insulation layers of the home. When moisture reaches these components, it can lead to wood rot, mold growth, and structural failure. A well-functioning siding will protect a home against these everyday hazards as well as various types of natural disasters.

    Ensuring Success
    1. Ensure the engineer, architect, plans examiner, builder, siding contractor and other relevant parties have created and reviewed plans for the siding details.
    2. Ensure there is a plan for how to detail the siding outside corner, inside corner, and transitions to a window, door, foundation, and soffit. Additional detail can include the transition point between siding materials. Developing details that shed water and allow adequate drying is essential to the longevity of the siding and the wall assembly.
    3. Review these details and the manufacturer’s specification and best practices with the siding installers and laborers prior to work.
    4. Install siding products in accordance with manufacturer’s specification and best practices.
    5. Ensure siding installers and laborers are properly trained to safely work with the material and its proper application.
    6. Document the installation with photos.
    Climate

    Hurricane and High Wind Regionsg

    Regions that are at especially high risk of wind-borne debris impacting the home’s siding, windows, and doors, including  are shown on the map Figure 1). Exterior finish materials should be durable against impacts from a fast-moving object carried by the wind.

    Wind-Borne Debris Regions of Florida, Category II and III Buildings
    Figure 1. Wind-Borne Debris Regions of Florida, Category II and III Buildings (Source: Florida Building Code 2010, Figure 1609A). 

     

    Homes located in Miami-Dade and Broward counties in Florida are required by the Florida State Building Code to use building materials that are approved and tested to meet the impact requirements of the High Velocity Hurricane Zone (Figure 2). Please refer to the database of approved products on the Florida Department of Business and Professional Regulation website.

    The Wind-Borne Debris Regions and High-Velocity Hurricane Zone in Florida
    Figure 2. The Wind-Borne Debris Regions and High-Velocity Hurricane Zone in  Florida (Source: Courtesy of Therma-Tru 2018). 

     

    Tornadoes

    Tornados are another source of high winds and driver of wind-borne debris. The map below shows the tornado risk for various parts of the continental United States (Figure 3).

    Average number of tornadoes per year across the United States
    Figure 3. Average number of tornadoes per year across the United States (Source: University Corporation for Atmospheric Research (UCAR) Center for Science Education 2013). 

     

    Fire Risk

    The USDA Forest Service’s Fire Modeling Institute produces maps that evaluate the wildfire hazard potential based on fuel levels and weather patterns; see Figure 4 for a map of the entire United States. Local maps are available. If you find that your home is located in a high wildfire hazard potential area, take precautions including selecting a siding material that doesn’t burn or melt.

    Wildfire Risk Map of the United States.
    Figure 4. Wildfire Risk Map of the United States (Source: USDA 2020). 

     

    Termite Risk

    Rodents, birds, various insects, and other pests are present throughout the United States.

    The termite risk is heavily geographically dependent. Figure 5 shows the likelihood of termite infestation across the United States.  

    Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
    Figure 5. Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7) (Source: Courtesy of PNNL).

     

    Flooding Risk

    FEMA has produced highly detailed maps delineating the flood risk at any address. Figure 6 shows an example of one of these maps for Portland, Oregon. FEMA provides an online mapping tool called the FEMA Flood Risk Map for finding the flood risk at any given U.S. address.

    FEMA Flood Risk Map for Specific Locations – Example Portland, Oregon.
    Figure 6. FEMA Flood Risk Map for Specific Locations – Example Portland, Oregon (Source: FEMA). 

    Earthquake Risk

    The USGS develops national seismic hazard maps. Figure 7 shows seismic risk for the United States. Homes that are located in a high earthquake risk location should select siding materials that are sufficiently ductile so that they don’t crack from the sudden movements of an earthquake.

    Seismic Risk Map of the United States
    Figure 7. Seismic Risk Map of the United States (Source: USGS).

     

    Videos
    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.

     

    2009 International Energy Conservation Code (IECC)

    Section R402.4 specifies that the home should be constructed to limit air leakage. Section 402.4.1 indicates specific areas to be caulked, gasketed, or sealed, including all joints, seams, and penetrations. Section 402.4.2 specifies that air leakage should be tested with an extensive visual inspection or with a blower door test with a maximum air leakage of <7 ACH 50.

    2012, 20152018 IECC, and 2021 IECC

    Section R402.4 specifies that the home should be constructed to limit air leakage and should be blower door tested to confirm air leakage is <5 ACH 50 in Climate Zones 1-2 and <3 in Climate Zones 3-8. Table R402.4.1.1 specifies the installation of a continuous air barrier and notes specific air barrier details.

    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, 2021). 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)

    Sections R318.1 – R318.3 describe control methods including field-applied chemical treatments for soil and wood and metal or plastic barriers including shields on top of foundation walls. Section R318.4 notes that in areas indicated as having a very heavy probability of termite infestation, as shown in the termite probability map in 2009 IRC Figure R301.2(6) (R301.2(7) in 2018 IRC), rigid foam including extruded or expanded polystyrene, polyisocyanurate and other foam plastics should not be installed on the exterior face of foundation walls or under foundation walls or slabs below grade and, if foam is applied on exterior above-grade walls, there must be at least six inches of clearance between the foam and the soil surface. There are exceptions to this restriction: if all structural members of the building are made of noncombustible or pressure-preservative-treated wood, or the foam is protected by some approved method, or if the foam is installed on the interior of basement walls.

    Figure R318.4 in the 2021 IRC (R301.2(7) in 2018 IRC, R301.2(6) in 2009, 2012, and 2015 IRC) is a Termite Infestation Probability Map, determining if the home will be constructed in an area of very heavy, moderate-to-heavy, slight-to-moderate, or none-to-slight termite infestation.

    Information about the code minimum requirements for every common siding material can be found in Chapter 7 of the International Residential Code.

    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.

     

    ASTM E2925-14 Standard

    A rainscreen that meets the ASTM E2925-14 Standard Specification for Manufactured Polymeric Drainage and Ventilation Materials Used to Provide a Rainscreen Function will be a minimum of 3/16-inch or greater.

     

    2009, 2012, 2015, 2018, & 2021 International Wildland Urban Interface Code

    Section 502.1 and Section 503.1.

    The IWUIC determines the class of ignition-resistance in the wildland-urban interface in Table 503.1 by evaluating the fire hazard severity of the site using IWUIC Table 502.1, combined with evaluations of defensible space conformance, and water supply conformance.

    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  

    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.

     

    Brick Industry Association

    The Brick Industry Association provides a guide (#27) for determining the frequency of the weep holes and where and how often to compartmentalize the rain screen cavity.

     

    National Concrete Masonry Association

    The National Concrete Masonry Association provides a guide for the proper installation of manufactured stone veneers including guidance on the rainscreen size, metal lath selection, lath fastener spacing pattern, and an inspection checklist.

     

    International Masonry Institute

    The International Masonry Institute website contains hundreds of details for brick, block, and stone masonry systems that can be used in your construction project specifications.

     

    Earth Advantage

    Earth Advantage is both an above code certification organization and a standards creation body. Their Earth Advantage Residential Measures Resource Guide provides hundreds of best practices for residential single-family homes including ones for walls and siding.

    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

    Siding materials and installations that have been damaged by either a storm, natural disaster, or years of weathering should be evaluated to see whether the damage can be repaired or whether a complete replacement of the siding is necessary. Replacement of siding on an older home offers the opportunity to ensure that air sealing, insulation, flashing, and drainage plane layers are inspected and corrected for proper installation as well. Additionally, siding replacement could be an optimal opportunity to upgrade knob and tube wiring in wall cavities, remove and remediate mold, repair water damage and flashing, correct structural and framing integrity deficiencies, remove lead paint, and implement pest guards.

    A siding replacement is also an excellent time to add wall insulation to the wall cavities using blown cellulose or fiberglass and/or to the exterior of the walls using rigid foam that can serve as a continuous thermal break and air barrier as well as a drainage plane depending on the product and if the seams are taped. Consult with a rater, see your local building code, other guides in the Solution Center, and the Building America Building Science Advisor for guidance on how much and what type of insulation to add to avoid moisture condensation in the walls in your locale.

    A siding replacement can also be a very good time to upgrade windows because flashing details around the window can be properly implemented and integrated with the building’s other control layers.

    In a fire-prone area, if the home is sided with a combustible siding, regardless of the condition of the siding, recommend replacing combustible siding with non-combustible siding. If the homeowner’s budget does not allow full replacement, recommend replacing combustible siding with noncombustible siding on dormers or other vertical wall locations that abut roofs and along the lowest part of the first-story walls where woody debris is more likely to collect, and at locations where walls abut wood decks to provide protection against flame spread, until the homeowner can afford to replace all of the home’s siding (IBHS 2019).

    Please refer to Building America Solution Center pre-retrofit assessment of walls, windows, and doors guide for safety considerations when implementing these measures.

    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)
    Siding Cost Guide
    Organization(s)
    Siding Cost Guide
    Publication Date
    Description
    A starting point for ballparking and comparing the cost of different siding materials and a brief overview of the pros and cons of different siding materials.
    Author(s)
    Baechler,
    Gilbride,
    Hefty,
    Cole,
    Adams,
    Noonan,
    Love
    Organization(s)
    Pacific Northwest National Laboratory,
    Oak Ridge National Laboratory
    Publication Date
    Description
    Report describing measures that builders in mixed-humid climates can use to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.
    Author(s)
    Earth Advantage
    Organization(s)
    Earth Advantage
    Publication Date
    Description
    A guide about the above code residential home certification called Earth Advantage and required and optional measures available to meet the point requirements for certification.
    Author(s)
    City of Newberg Oregon
    Organization(s)
    City of Newberg Oregon
    Publication Date
    Description
    An example of a form a building codes department created to ensure builders are fully aware and have taken steps to provide drainage so that water doesn’t accumulate behind siding. This example is from the city of Newberg, Oregon.
    Author(s)
    Mark Parlee
    Organization(s)
    Journal of Light Construction
    Publication Date
    Description
    A story about how omission of two small but critical wall details, a kick-out flashing and a weep screed, lead to extensive water damage to a wall.
    Author(s)
    Stephen T. Peters,
    Ian N. Robertson
    Organization(s)
    University of Hawaii College of Engineering
    Publication Date
    Description
    Projectile missile testing of various wall panel configuration to understand how the different wall constructions would perform when struck with wind driven debris from a hurricane.
    Author(s)
    Richard Bennett,
    Gregg Borchelt,
    Jim Bryja,
    Bill Kjorlien
    Organization(s)
    Canadian Masonry Design Center
    Publication Date
    Description
    An impact test report from projectile missile tests against brick veneer, verifying that brick veneers perform well to resisting hurricane force wind driven debris.
    Author(s)
    Scott Kashuba,
    Marc Kuzik,
    Michael Hatzinikolas
    Organization(s)
    The Canadian Masonry Research Institute
    Publication Date
    Description
    Testing of various siding materials for their ability to resist bullets from small firearms.
    Author(s)
    International Code Council,
    Florida Building Commission
    Organization(s)
    ICC,
    FBC
    Publication Date
    Description
    Florida building code including all the amendments and additions by Florida for the wind-borne debris regions and the high-velocity hurricane zone.
    Author(s)
    Quarles,
    Pohl
    Organization(s)
    USFS,
    IBHS
    Publication Date
    Description
    Report examining the cost differences between a typical home and a home constructed using wildfire-resistant materials and design features.
    Author(s)
    CAL FIRE Fire Engineering Division
    Organization(s)
    CAL FIRE Fire Engineering Division
    Publication Date
    Description
    A list of exterior building products and materials approved for use in wildland urban interface zoned homes. These products are non-combustible or ignition-resistant.
    Author(s)
    Department of Resource Management Building Division
    Organization(s)
    County of Shasta California
    Publication Date
    Description
    An example of wildland urban interface construction requirements for new buildings built in very high fire risk zones/areas.
    Author(s)
    Marija Jelčić Rukavina,
    Milan Carević,
    Ivana Banjad Pečur
    Organization(s)
    University of Zagreb
    Publication Date
    Description
    A guide for designers, architects, engineers, and fire experts on how to design rainscreen and ventilated cavities such that they don’t contribute to the spread of a fire.
    Author(s)
    Firetherm
    Organization(s)
    Firetherm
    Publication Date
    Description
    An example of commercially available thermally expansive fire stopping products for controlling the spread of fires in a rainscreen cavity.
    Author(s)
    U.S. Forest Service
    Organization(s)
    USDA
    Publication Date
    Description
    An introduction to the insect termites.
    Author(s)
    Cassie Krejci,
    John Muncaster
    Organization(s)
    TERM Barriers by Polyguard Products
    Publication Date
    Description
    An article describing a way to protect drain and ventilation holes in brick veneer siding against pest. Selecting a fine screen mesh opening (1/55-inch or 0.5-mm) is important to guard against small insects such as subterranean termites.
    Author(s)
    Federal Emergency Management Agency
    Organization(s)
    FEMA
    Publication Date
    Description
    A guide aiming to assist local officials and community decision makers in coastal areas in adopting and implementing sound mitigation measures to lower building natural disaster vulnerability.
    Author(s)
    International Code Council
    Organization(s)
    ICC
    Publication Date
    Description
    2018 edition of code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less, bringing together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.
    Author(s)
    Florida Department of Business & Professional Regulation
    Organization(s)
    Florida Department of Business & Professional Regulation
    Publication Date
    Description
    Database of approved products that meet the requirements of the High Velocity Hurricane Zone.
    Author(s)
    University Corporation for Atmospheric Research Center for Science Education
    Organization(s)
    University Corporation for Atmospheric Research Center for Science Education
    Publication Date
    Description
    A heat map showing the average number of tornadoes per year across the United States
    Author(s)
    United States Department of Agriculture
    Organization(s)
    USDA
    Publication Date
    Description
    Webpage from USDA and U.S. Forest Service with a map of potential wildfire risk across the U.S.
    Author(s)
    Federal Emergency Management Agency
    Organization(s)
    FEMA
    Publication Date
    Description
    A address searchable geographic information system for visualizing the flood hazard of an address and its surrounding area.
    Author(s)
    U.S. Geological Survey
    Organization(s)
    USGS
    Publication Date
    Description
    Website providing a probabilistic map of the expected number of damaging earthquakes around the U.S.
    Author(s)
    Mark Parlee
    Organization(s)
    The Building Consultant
    Publication Date
    Description
    An article illustrating common errors found in fiber cement siding installations. Many of these errors and poor flashing examples apply to siding materials beyond fiber cement siding.
    Author(s)
    Todd Fratzel
    Organization(s)
    Home Construction and Improvement
    Publication Date
    Description
    A article about the best practice method of installing fiber cement siding, to install flashing at the butt joints of the siding boards, rather than face caulking the butt joints afterwards.
    Author(s)
    Don Jackson
    Organization(s)
    The Journal of Light Construction
    Publication Date
    Description
    An article written by Don Jackson of The Journal of Light Construction on how to detail brick veneer siding wall.
    Author(s)
    Bill Stephan
    Organization(s)
    Metropolitan Engineering Consulting and Forensics Services
    Publication Date
    Description
    An article about how mortar droppings during the installation of a brick veneer can clog the weep holes in the wall assembly causing moisture damage. The article also illustrates products that can be installed in the ventilated cavity to mitigate this problem.
    Author(s)
    Building Enclosure Moisture Management Institute
    Organization(s)
    Building Enclosure Moisture Management Institute
    Publication Date
    Description
    A presentation about the need for rainscreens including the damage water and moisture ingress into a home’s siding and framing can cause, and ways to design a resilient wall that drains and ventilates well.
    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)
    Metal Sales Manufacturing Corporation
    Organization(s)
    Metal Sales Manufacturing Corporation
    Publication Date
    Description
    Installation manual for installing metal panel siding.
    Author(s)
    Oak Ridge National Laboratory,
    U.S. Department of Energy
    Organization(s)
    ORNL,
    DOE
    Publication Date
    Description
    Web based tool providing decision-making guidance for selecting wall assembly components.
    Author(s)
    Cal Fire Office of the State Fire Marshal
    Organization(s)
    Cal Fire
    Publication Date
    Description
    California Office of the State Fire Marshal's homepage for the Building Materials Listing Program, providing builders, contractors, architects, and others with access to a database of fire alarm systems and fire-resistant construction materials including roof coverings, wall, ceiling, and floor...
    Author(s)
    Hammer & Hand
    Organization(s)
    Hammer & Hand
    Publication Date
    Description
    This Best Practices Manual is the product of Hammer & Hand’s ongoing work to document and internally codify our standard operating procedures for construction practice.
    Author(s)
    American Society for Testing and Materials
    Organization(s)
    ASTM
    Publication Date
    Description
    Specification describing criteria for manufactured polymetric materials used to provide a rainscreen function, a means for the drainage of liquid moisture and the ventilation of vapor moisture that enters an above-grade exterior wall assembly.
    Author(s)
    National Concrete Masonry Association
    Organization(s)
    National Concrete Masonry Association
    Publication Date
    Description
    Article providing guidance for installing manufactured stone veneer, including information on rainscreens.
    Author(s)
    International Masonry Institute
    Organization(s)
    International Masonry Institute
    Publication Date
    Description
    Webpage featuring hundreds of illustrations of masonry construction details for brick, congrete, stone, tile, stucco, etc.
    Author(s)
    Joseph Lstiburek
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Guide from Building Science Corporation on how to construct a flood and hurricane resistant home.
    *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.

    Pacific Northwest National Laboratory

    Last Updated

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