Decks are Wildfire-Resistant

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    A deck or other attached structure located at the top of a slope with vegetation underneath is at high risk of ignition during a wildfire
    Scope

    Use fire-resistant materials and consider siting and vegetation if constructing attachments to a home, such as decking, fencing, railings, balconies, porches, stairs, ramps, columns, or carports, to reduce the risk of fire damage to these attachments and subsequently to the house in the event of a wildfire.

    • Don’t site decks and other attachments to the house near heavily vegetated areas or at the tops of vegetated ravines, steep slopes, canyons, ridges, etc. Set decks back 50 feet from the tops of vegetated wildland slopes. Clear away vegetation beneath and around decks. Remove or cut back trees so branches are more than 10 feet from decks. Landscape with low-fire-risk ground covers.
    • Use heavy timber, noncombustible, or fire-resistant materials to construct the deck or other attached structures.
    • For existing decks, replace combustible materials with noncombustible or fire-resistant materials.
    • Screen or box-in areas below decks to prevent debris accumulation. Box in the area beneath the deck with noncombustible or fire-resistant siding or ≤1/8-inch metal mesh screen. 

    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

    In wildfire-prone areas, decks and other attached structures such as balconies, porches, railings, fences, columns, stairs, and ramps that are made out of combustible materials are at high risk of catching fire in a wildfire, and flames and embers from these structures can damage or destroy the home.

    During a wildfire event, structures primarily catch fire through fire brands and embers that come in direct contact with combustible materials on or around the home, wind-borne embers that enter the home through unscreened vents or open or broken windows, radiant heat transfer from structure to structure or from vegetation to structure, and in a small percentage of cases, from direct contact with the flaming front of a moving wildfire. Typically, in wildland fire situations, the flaming front passes an area in a matter of minutes. Studies conducted by the Missoula Fire Science Laboratory, as reported in the “Ignition-Resistant Construction Guide” by FireSafe Montana, show the most prominent method of initial ignition to a structure is through fire brands and embers. Additionally, research shows that homes are more likely to be ignited by the radiant heat of an approaching fire than to be ignited by direct flame contact from the actual fast-moving fire front (FireSafe Montana 2010).

    Conventional wooden decks are so combustible that when a wildfire approaches, the deck often ignites before the fire reaches the structure (CSFS 2012). Normally, decks ignite in one of three ways:  1) a burning brand lands and ignites dry deck boards, especially if there are wide gaps between the boards which allow airflow and harbor embers; 2) the deck is burned from below by direct flame from unmaintained vegetation or debris under the deck which catches fire, or 3) flames spread from combustible materials nearby. Heat from a deck fire can then cause the glass in a sliding door to break or cause combustible siding or soffits to ignite (CSFS 2012, University of California 2021).

    Homes at the tops of vegetated slopes are especially vulnerable because fire travels swiftly uphill and fire-induced updrafts will carry heat forward, preheating and drying uphill vegetation and structures in the path of an oncoming fire. Structures that project from the home such as decks, soffits, and balconies can trap flames and heat from an approaching wildfire. These are areas of intense heat, including some of the highest temperatures measured on a home during a wildfire (Milne 2021). Homes should be set 50 feet back from wildland vegetation on unmaintained canyons and slopes and any structures attached to the home should be constructed of noncombustible materials and designed, located, and landscaped in a way that minimizes the risk of catching fire in a wildfire. The decks in Figure 1 employ several fire-safe measures. The exposed parts are made of nonflammable material, the wood supports on the undersides are covered with fiber cement boards, and there is more defensible space around the home with more than 30 feet of ground cover with low likelihood of ignition (rocks, irrigated lawn, concrete sidewalk) between the decks and woody vegetation (Figure 1).

    These wildfire-resistant decks have a solid decking surface, metal railings, and the underside timber supports are covered with flame-resistant fiber cement board; also the decking is separated from the vegetated slope by more than 30 feet of low-fire-risk ground cover
    Figure 1. These wildfire-resistant decks have a solid decking surface, metal railings, and the underside timber supports are covered with flame-resistant fiber cement board; also the decking is separated from the vegetated slope by more than 30 feet of low-fire-risk ground cover (Source: Courtesy of PNNL).

    Steps to Reduce Wildfire Risk for Decks and Other Attachments

    When constructing decks and attachments, there are practices builders can employ associated with each of these steps to reduce the risks of wildfires: 1) siting, 2) choosing materials, 3) designing and constructing the deck. These recommendations, provided below, are based on guidance from the Federal Energy Management Agency (FEMA)’s Home Builder's Guide to Construction in Wildfire Zones: Technical Fact Sheet Series (FEMA P-737 2008) and the Colorado State Forest Services’ FireWise Construction: Site Design & Building Materials (CSFS 2012), among others.

    Step 1 – Siting

    Select a site for the deck that will lower the risk of fire damage to the deck and therefore to the home. Three things related to siting can impact the spread of wildfires: fuel, weather, and topography.

    Fuel - Fuel is anything that is flammable, such as vegetation, wood piles, wooden structures, fuel tanks, outdoor furniture, and debris. Any time there is a fuel path that fire can follow to reach a home or deck, there is a high risk of ignition. The area immediately around the home should be cleared of vegetation, wood piles, and other flammable materials that can serve as fuel for a wildfire. When firefighters triage an area during a wildland fire, because of limited resources, they may determine that homes that do not have defensible space are unsaveable.

    To create a “defensible space” around the home (National Fire Protection Association 2021), the immediate zone within 5 feet of the perimeter of the home and attached structures should be as free of combustibles as possible (Figure 2). The intermediate zone, within 5 to 30 feet of the home, should have minimal combustibles and the canopies of mature trees (or clusters of two or three trees) should be spaced at least 18 feet apart. In the extended zone, from 30 to 100 feet from the home, fuels should still be reduced from what might be found in surrounding woodlands. From 30 to 60 feet away from the home, trees should be minimal and canopies should be at least 12 feet apart. From 60 to 100 feet, the canopies of mature trees should be at least 6 feet apart, although more is better. In all cases, undergrowth should be minimal and lower branches should be removed up to 6 to 10 feet up from the ground depending on the tree’s height at the time of pruning. (See the website “Preparing Homes for Wildfire,” National Fire Protection Association 2021 and the guide “Design Site for Defensible Space for Protection Against Wildfires,” FEMA P-737 2008, for more information on defensible space.)

    Create defensible space around the home to protect it from wildfires.
    Figure 2. Create defensible space around the home to protect it from wildfires (Source: adapted from National Fire Protection Association 2021).

    Radiant heat from a fire can preheat and even ignite structures. Firefighters have seen radiant heat through windows ignite interior contents of the home as well. Radiant heat transfer is most pronounced in the first 10 feet from the heat source but is still perceptible at 30 feet away (see Figure 3). For this reason, fuel sources like trees should be planted at least 30 feet from structures if possible (CSFS 2012).

    Radiant heat energy from fires decreases with distance from the flames but is intense enough at close range to cause ignition
    Figure 3. Radiant heat energy from fires decreases with distance from the flames but is intense enough at close range to cause ignition (Source: CSFS 2012).

    To summarize deck construction guidance related to wildfire fuels,

    • Avoid a site on or near vegetation that cannot be cleared away.
    • Create defensible space around the home. In the immediate area around the house and deck, install a noncombustible ground cover to ensure no ground near the deck will ignite. Noncombustible ground covers include rock, gravel, pavers, and composted or heavy bark mulch.
    • If wooden fencing is planned, switch to a noncombustible fencing material for the 5 to 10 feet closest to the house.
    • Discuss landscaping choices with the homeowner. Recommend installing patios, pavers, stone paths, and gravel near the home, and maintained lawns, vegetable gardens, lower shrubs, and smaller trees within 100 feet of the home. Provide guidance to homeowners on keeping the area around the home free of weeds and debris. Direct them to resources on ignition-resistant plants that may be safer to plant near the home, such as Fire-Smart Plants - Choosing Landscaping Plants in a Fire-Prone Environment (FIRESafe Marin 2020).

    Weather – In dry, windy conditions, fuels that may have seemed well out of reach of an approaching wildfire can suddenly come within reach and under threat of ignition. Consider prevailing winds when locating structures and know that drier climates may require greater distances when creating defensible space.

    Topography - Topography deals with the steepness and direction of slopes. While many homeowners want a deck jutting out over a hillside or canyon, sites like this are very vulnerable to wildfires (Figure 4). Topographic features such as steep slopes, gullies, canyons, saddles, ridge tops, and narrow mountain passes can focus surface winds and encourage updrafts that spread fire much faster than it would spread on flat ground (see Figure 5).

    Decks that extend over vegetated slopes are very vulnerable to ignition by approaching wildfires
    Figure 4. Decks that extend over vegetated slopes are very vulnerable to ignition by approaching wildfires (Source: CSFS 2012).
    Flames spread faster on steeper slopes
    Figure 5. Flames spread faster on steeper slopes (Source: National Wildfire Coordinating Group 2021). 

    Several factors contribute to the spread of fires on slopes (National Wildfire Coordinating Group 2021):

    • Wind currents are normally uphill and this tends to push heat and flames up into new fuels.
    • Convection heat from the flames rises along the slope causing updrafts which further increase the rate of spread.
    • The rising heat and wind that precede a fire traveling uphill carry burning embers and also preheat and dry the fuel ahead of the flames.
    • On the uphill side, the fuel ahead of the flame front is closer to the flames than if the slope were flatter. 
    • Burning embers and chunks of fuel may roll downhill into unburned fuels, increasing the spread by starting new fires.
    • The steeper the slope, the faster the fire will move. The first tripling of slope increases the rate of fire spread by a factor of 2 and the second tripling of slope increases the rate of spread by a factor of 4 to 6, depending on fuel conditions; therefore, fire traveling up a 9% grade can travel 6 to 8 times as fast as fire traveling across flat ground (National Wildfire Coordinating Group 2021).
    • South-facing slopes tend to burn more readily than north-facing slopes because the vegetation (fuel) on those slopes is typically warmer and drier (Canada Northwest Territories Department of Environment and Natural Resources 2021). 

    Here are some siting considerations to keep in mind (FEMA P-737 2008):

    • Avoid selecting a construction site along a gully or in a narrow canyon, in or adjacent to a saddle or narrow mountain pass, on or adjacent to a steep slope.
    • If a ridgetop site is selected, choose an area that allows for a minimum 50-foot setback from wildland vegetation on the downslope side. Increase the setback at sites with heavier fuels such as in a forested environment.

    Step 2 – Choosing Building Materials

    After the site for the deck is chosen according to the guidelines listed above, low-fire-risk building materials should be chosen. Decks, and other projections from the home like balconies, carports, patio covers, etc., should be constructed of heavy timber, noncombustible materials like metal or concrete, or exterior-rated fire-retardant-treated wood or ignition resistant materials (NFPA 1144, FEMA P-737 2008). Although wood is a very popular deck construction material, it requires significant maintenance to keep it from drying out and splitting, which makes it very susceptible to catching embers and igniting (FireSafe Montana 2010, FEMA P-737 2008).

    • For the pier supports, if using wood, use minimum 6x6-inch timbers. Other recommended column materials are concrete block or steel posts set in concrete.
    • For floor joists and beams, use heavy timber, 3-inch to 4-inch nominal thickness, fire-retardant-treated wood, or concrete block or steel framing.
    • For deck railings, use minimum 3-inch nominal thickness fire-retardant-treated wood or instead use metal, cables, or tempered glass.
    • For decking and stair treads, use exterior fire-retardant-treated wood with minimum 3-inch nominal thickness. Other options for decking and stairs include composite decking, or brick or concrete pavers that have a suitable drainage mat under the pavers and over the wood or metal grate deck surface. Light poured concrete may also be a suitable deck covering.
      • When decks are subject to embers and fire brands, wooden deck surfaces are more easily ignited than composite decks, which tend to melt but not ignite (FireSafe Montana 2011).
      • Solid-construction composite materials have performed well under test conditions, but not as well as heavy timber. Composite decking is recommended as a significant defense against brand and ember-initiated ignition of homes by FireSafe Montana (Ignition Resistant Construction Guide 2010). IBHS also advises that higher-density deck boards including some brands of wood-plastic composite and tropical hardwood deck board, are more resistant to direct ember ignition than untreated wood boards (IBHS 2019).  
      • Do not use plastic and composite decking materials with underside channels or hollow plastic or composite materials as they have been shown to collapse or degrade quickly when exposed to fire (FEMA P-737 2008).
    • Follow the guidelines from 2021 IWUIC, Table 503.1, Ignition-Resistant Construction. See the Compliance Tab for more details.

    Flame Spread and Ignition Resistance Ratings

    Like roofing materials, building products are tested for surface burning characteristics and given a rating classification depending upon how well they resist ignition and spread of flame across the surface. The flame spread classification has three levels: Class A, Class B, and Class C, with Class A having the best performance at resisting flame spread. Most natural wood products have a Class C rating unless treated for ignition resistance. Many composite or PVC decking materials are available with a Class B rating and some have a Class A rating.

    The International Wildland Urban Interface Code (IWUIC) requires that structures constructed in WUI areas meet the requirements of Class 1, Class 2, or Class 3 ignition-resistant construction, based on the fire hazard likelihood of the location. The Uniform Building Code UBC uses the Class 1, 2, and 3 designations and the International Building Code (IBC) uses A, B, and C designations. The requirements of these ignition-resistant construction classes are based on the fire hazard severity of the site. Class 1 provides the most protection and should be used for areas of extreme fire hazard; Class 2 provides protection in areas of high fire hazard; and Class 3 provides some protection over traditional construction requirement for areas of moderate fire hazard.

    Table 1 shows the deck and attachment materials requirements of IWUIC Sections 504, 505, and 506, which define the Class 1, Class 2, and Class 3 requirements, respectively (CSFS 2012). In the table “noncombustible” refers to a material that will not ignite and burn when subjected to fire, per ASTM E-136 “Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C.”  Examples include concrete, steel, and brick masonry. Hourly fire-resistance ratings are based on ASTM E-119 “Fire Tests of Building Construction Materials.” The flame-spread categories are defined by ASTM E-84/UL 723:

    • Class A or 1: Flame-spread index of 25 or less (Fire-Retardant-Treated Wood or FRTW)
    • Class B or 2: Flame spread index of 26 to 75 (some untreated lumber)
    • Class C or 3: Flame spread index of 76 to 200 (most untreated lumber and plywood).

    Table 1. Ignition-Resistant Construction Material Requirements for Decks, based on the Fire Hazard Severity of the Location , per the IWUIC (excerpted from CSFS 2012).

    Architectural Feature

    Class 1 (Extreme Severity)

    Class 2 (High Severity)

    Class 3 (Moderate Severity)

    Appendages and projections, such as decks

    1-hour fire resistance from the exterior side, or
    Heavy timber construction, or
    Approved noncombustible materials, or
    Exterior fire-retardant-treated wood, or
    Ignition-resistant building material

    1-hour fire resistance from the exterior side, or
    Heavy timber construction, or
    Approved noncombustible materials, or
    Exterior fire-retardant-treated wood, or
    Ignition-resistant building materials

    No special requirement

     

    Step 3 – Designing and Constructing the Deck

    Before constructing the deck, consider design. Is a deck necessary? For first-floor decks, rather than climbing wooden stairs up to a wooden deck, would concrete steps down to a concrete or stone paver patio work instead?

    If a deck is desired, the safest design is one that is fully enclosed underneath, with walls made of fire-resistant cladding to completely eliminate the potential fire trap, as described in the guide FireWise Construction from the Colorado State Forest Service (CSFS 2012) (Figure 6). The deck can be enclosed vertically by installing a flame-resistant exterior siding product around the perimeter like fiber cement, stucco, stone, brick or metal, fire-retardant-treated plywood (ignition resistant), gypsum sheathing (noncombustible), or metal screen. The enclosed below deck also complies with the International Wildland-Urban Interface Code. Enclosing the deck can increase the possibility of moisture-related degradation of wood structural support members and metal fasteners if proper drainage and ventilation is not provided (CSFS 2012). The below-deck area can be enclosed with metal screening with mesh finer than 1/8 inch to keep out embers and debris while providing ventilation (IBHS 2019). Flammable products like wood lattice should not be used for enclosing decks in wildfire areas.

    Enclosing the area below the deck minimizes fire risk in several ways:

    • Minimizes airflow up through the deck, which could draw burning embers under the deck.
    • Prevents the entry of wind-blown firebrands and embers under the deck where they could lodge and catch the deck boards or supports on fire from underneath.
    • Prevents vegetation from growing under the deck. Keeps leaves, pine needles, and other potentially flammable debris from accumulating under the deck.
    • Discourages the occupants from storing flammable items under the deck, such as firewood, boxes, spare lumber, etc. (FireSafe Montana 2010). The space beneath the deck can be used for storage if it is walled in or fenced in with 1/8-inch metal mesh; 1/16-inch is preferable (CSFS 2012).
    Fully enclosing the area under the deck increases its resistance to wildfire by minimizing the space where embers can lodge
    Figure 6. Fully enclosing the area under the deck increases its resistance to wildfire by minimizing the space where embers can lodge (Source: CSFS 2012).

    For high, narrow decks that might include a doorway or walkway below, like the deck shown in Figure 1, the wood support framing can be enclosed horizontally by installing an exterior flame-resistant product like fiber cement panels to the underside of the support joists. This will minimize airflow up through the deck, which could draw burning embers up in between the deck boards. It will also minimize spaces for embers to catch in joints or cracks between wooden deck supports and deck boards. To provide drainage, ¼-inch weep holes should be drilled into the underside panel to allow water that leaks through the decking to drain out of the soffit space (FEMA P-737 2008).

    Another protective measure for decks on vegetated slopes is to construct a non-combustible patio and wall down the slope from the deck. The wall can act as a shield to deflect both the radiant and convective energy of the fire away from the deck (See Figure 7, CSFS 2012.) The wall should be made of a noncombustible material and should be located within approximately 20 feet of the deck to help deflect the flames of an uphill-burning fire. As recommended in NFPA 1144 (Standard for Reducing Structure Ignition Hazards from Wildland Fire), these walls should be about 6 feet tall (IBHS 2019).

    A patio and wall constructed of noncombustible concrete, stone, or brick helps to deflect heat protect the deck and house from approaching wildfires.
    Figure 7. A patio and wall constructed of noncombustible concrete, stone, or brick helps to deflect heat protect the deck and house from approaching wildfires. (Source: CSFS 2012).

    Another construction alternative is heavy timber construction. Like log construction, heavy timber is combustible but so thick that it burns very slowly. Posts and supports should be at least 6 inches thick and decking and railings should be at least 3 inches thick. (See Figure 8, CSFS 2012.)

    Heavy timber deck construction uses slow-burning timbers 3 inches or thicker to reduce the flammability of the deck
    Figure 8. Heavy timber deck construction uses slow-burning timbers 3 inches or thicker to reduce the flammability of the deck (Source: CSFS 2012).

    In high-fire-hazard areas, consider constructing the deck of noncombustible surfaces, fire-retardant-treated wood, and fire-resistive building materials. As described in the guide FireWise Construction from the Colorado State Forest Service (CSFS 2012) wood frame construction is permitted, but the surface should be composed of noncombustible, fire-retardant-treated, or one-hour fire-resistive materials. To build a solid-surface noncombustible deck, place a waterproof membrane over the top of the deck. Cover the membrane with fire-retardant-treated lumber decking, or use 1 to 2 inches of concrete or stone. This surface is ignition resistant and protects the deck from airborne embers but will require that the structure be strengthened to support the additional weight. Posts and railings can be built from steel. Wood posts near the ground can have stone, brick, or noncombustible coverings or be of fire-retardant-treated wood. A popular, but expensive, baluster design is steel wire. Steel pipe, usually 1 to 2 inches in diameter, is more economical and easy to work with. Square steel shapes can look like traditional wood railings (CSFS 2012).

    Fire-resistant deck construction using a solid, nonflammable deck surface and materials
    Figure 9. Fire-resistant deck construction using a solid, nonflammable deck surface and materials (Source: CSFS 2012).

    General considerations when constructing a deck in wildfire-prone areas include the following:

    • Avoid using any wood, even wood types recommended above, that is chipped or has rough edges that fire can catch onto.
    • Avoid widely spaced deck boards that facilitate airflow. (See Figure 10.)
    • Use metal railings. (See Figure 10.)
    • Install metal flashing at the deck-to-house connection to provide additional protection against ignition at this location which has increased potential for accumulation of embers and brands (see Figure 11, FireSafe Montana 2010).
    • Once a deck is constructed according to these recommendations, instruct the occupants to keep the deck clear of debris, both on top of, below, and around the deck (Sierra Club 2017).
    • Enclose soffits above decks with solid, combustion-resistant material and cover the soffit vents with ≤ 1/8-inch wire mesh or design an unvented attic so that in the event the deck does catch fire, embers will not flow up the wall and get trapped in soffit framing or enter the soffit vents (FireSafe Montana 2010).
    • Install fire-resistant coverings on the underside of any cantilevers that overhang the deck (FireSafe Montana 2010).
    • Install a spark arrester on top of the home’s chimney so that the home’s fireplace does not become a source of burning embers that could ignite the deck or other attachments (FireSafe Montana 2010).
    • Fully enclose the area below the deck with solid walls made of fire-resistant material or with 1/8-inch metal screening. (See Figure 6.)
    Reduce the wildfire risks to decks by using closely spaced heavy lumber decking, heavy timber supports, and metal railings
    Figure 10. Reduce the wildfire risks to decks by using closely spaced heavy lumber decking, heavy timber supports, and metal railings (Source: FEMA P-737 2008).
    Heavy metal flashing protects the deck timbers and separates them from the wall at the wall-deck connection which is vulnerable to both ember entrapment and water damage
    Figure 11. Heavy metal flashing protects the deck timbers and separates them from the wall at the wall-deck connection which is vulnerable to both ember entrapment and water damage (Source: FEMA P-737 2008)

    Many decks are built of medium-density softwood decking materials such as redwood and cedar, which may be acceptable in low-wildfire-risk areas. However, they can still be vulnerable to ignition from wind-blown embers. The Insurance Institute for Business & Home Safety (IBHS) conducted research to evaluate how an ember-ignited fire on a deck made of redwood or cedar can spread to the home. They found that the primary cause of fires was embers that caught between narrowly spaced deck boards and started small smoldering fires which, in the presence of light winds, traveled slowly along the spaces between the boards until they reached the house. Fires also occurred when the flames spread down to the exposed tops of the support joists. These fires spread from joist to joist and then to the house if the joists were less than 16 inches apart. Based on these findings, IBHS recommends the following for softwood decks: 1) Increase the gap between deck boards from 1/8 inch to 1/4 inch. 2) Increase the joist spacing from 16 inches to 24 inches. 3) Apply a foil-faced self-adhering adhesive flashing tape (foil-faced bitumen tape) on the top of each joist (IBHS and NFPA 2021).

    Ensuring Success

    If the home is to be located in a wildland-urban interface (WUI) area, check local building codes regarding fire-resistant construction requirements.

    Climate

    Wildfires have historically been common in the mountains and western parts of the United States during the summer and fall months. However, wildfires can occur anywhere where vegetation is plentiful. See the map of wildfire potential in the United States.

    Wildfire Risk in the United States
    Figure 1. Wildfire Risk in the United States (Source: USDA Fire Labs 2018).

     General considerations when constructing a deck in wildfire prone areas include the following:

    • Avoid using any wood, even heavy timber, that is chipped or has rough edges that fire can catch onto.
    • Use noncombustible or fire resistant materials.
    • Avoid widely spaced deck boards that facilitate airflow.
    • Use metal railings.
    • Install metal flashing at the deck-to-house connection to provide additional protection against ignition at this location which has increased potential for accumulation of embers and firebrands.
    • Enclose soffits above decks with solid, combustion-resistant material and cover soffit vents with ≤1/8-inch wire mesh or design an unvented attic, so that in the event the deck does catch fire, embers will not flow up the wall and get trapped in soffit framing or enter the soffit vents (FireSafe Montana 2010).
    • Install fire-resistant coverings on the underside of any cantilevers that overhang the deck (FireSafe Montana 2010).
    • Install a spark arrester on top of the home’s chimney so that the home’s fireplace does not become a source of burning embers that could ignite the deck or other attachments (FireSafe Montana 2010).
    • Fully enclose the area below the deck with solid walls made of fire-resistant material or with 1/8-inch metal screening.
    • Once a deck is constructed according to these recommendations, instruct the occupants to keep the deck clear of debris, both on top of, below, and around the deck (Sierra Club 2017).
    Videos
    Publication Date
    Author(s)
    California Fire Science Consortium
    Organization(s)
    California Fire Science Consortium
    Description
    Video presentation explaining how homeowners can protect their property and home from wildfire ignition through defensible space and home retrofits.
    Publication Date
    Description
    Video explaining the threats of wildfires to homes and how to design your home to have a 'defensible zone' for fire protection. Recommendations from FLASH StrongHomes.
    Publication Date
    Author(s)
    UNRExtension
    Organization(s)
    UNRExtension
    Description
    Video presentation from the University of Nevada - Reno explaining fire-safe building materials and their classifications.
    Publication Date
    Author(s)
    UNRExtension
    Organization(s)
    UNRExtension
    Description
    Video presentation from the University of Nevada - Reno explaining how wildfires typically ignite structures and specific home retrofits homeowners can do to mitigate damage to their homes.
    Publication Date
    Author(s)
    Forest Service
    Organization(s)
    USFS
    Description
    Video from the Forest Service highlighting potential weak spots on homes that could ignite the structure and how to lower the chances of ignition in these key areas.
    Publication Date
    Author(s)
    FIRESafe Marin
    Organization(s)
    FIRESafe Marin
    Description
    Video from FIRESafe Marin explaining how decks can be a major weak point for embers to ignite. Proper construction and materials shown in the video reduce the risk of ignition.
    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, 2012, 2015, 2018, 2021 International Residential Code (IRC)

    R317.4 Plastic composites – Plastic composite exterior deck boards, stair treads, guards and handrails containing wood, cellulosic or other biodegradable materials shall comply with the requirements of Section R507.2.2.

    Section R302 – Fire-Resistant Construction includes material codes for fire-retardant construction.

    R507.3 Plastic composite deck boards, stair treads, guards, or handrails. Plastic composite exterior deck boards, stair treads, guards and handrails shall comply with the requirements of ASTM D7032 and the requirements of Section 507.3.

    R507.3.2 Flame spread index. Plastic composite deck boards, stair treads, guards, and handrails shall exhibit a flame spread index not exceeding 200 when tested in accordance with ASTM E 84 or UL 723 with the test specimen remaining in place during the test.

    Exception: Plastic composites determined to be noncombustible.

    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.

     

    2018, 2021 International Wildland-Urban Interface Code (IWUIC)

    501.3 Fire-Resistance-Rated Construction. Where this code requires 1-hour fire-resistance-rated construction, the fire-resistance rating of building elements, components or assemblies shall be determined in accordance with the test procedures set forth in ASTM E119 or UL 263.

    Exceptions:

    1. The fire-resistance rating of building elements, components or assemblies based on the prescriptive designs prescribed in Section 721 of the International Building Code.
    2. The fire-resistance rating of building elements, components or assemblies based on the calculation procedures in accordance with Section 722 of the International Building Code.

    502.1 General. The fire hazard severity of building sites for buildings hereafter constructed, modified or relocated into wildland-urban interface areas shall be established in accordance with Table 502.1. See also Appendix C.

    502.2 Fire Hazard Severity Reduction. The fire hazard severity identified in Table 502.1 is allowed to be reduced by implementing a vegetation management plan in accordance with Appendix B.

    503.1 General. Buildings and structures hereafter constructed, modified or relocated into or within wildland-urban interface areas shall meet the construction requirements in accordance with Table 503.1. Class 1, Class 2 or Class 3, ignition-resistant construction shall be in accordance with Sections 504, 505 and 506, respectively. Materials required to be ignition-resistant materials shall comply with the requirements of Section 503.2.

    503.2 Ignition-Resistant Building Material. Ignition-resistant building materials shall comply with any one of the following:

    1. Material shall be tested on all sides with the extended ASTM E84 (UL 723) test or ASTM 2768, except panel products shall be permitted to test only the front and back faces. Panel products shall be tested with a ripped or cut longitudinal gap of 1/8 inch (3.2 mm). Materials that, when tested in accordance with the test procedures set forth in ASTM E84 or UL 723 for a test period of 30 minutes, or with ASTM E2768, comply with the following:
      1. Flame spread. Material shall exhibit a flame spread index not exceeding 25 and shall not show evidence of progressive combustion following the extended 30-minute test.
      2.  Flame front. Material shall exhibit a flame front that does not progress more than 10.5 feet (3200 mm) beyond what the centerline of the burner at any time during the extended 30-minute test.
      3. Weathering. Ignition-resistant building materials shall maintain their performance in accordance with this section under conditions of use. <Materials shall meet the performance requirements for weathering (including exposure to temperature, moisture and ultraviolet radiation) contained in the following standards, as applicable to the materials and conditions of use:

    1.3.1 Method A “Test Method for Accelerated Weathering of Fire-Retardant-Treated Wood for Fire Testing” in ASTM D2898, for fire-retardant-treated wood, wood-plastic composite and plastic lumber materials.

    1.3.2. ASTM D7032 for wood-plastic composite materials.

    1.3.3. ASTM D6662 for plastic lumber materials.

      1. Identification. Materials shall bear identification showing the fire test results.

    Exception: Materials composed of a combustible core and a noncombustible exterior covering made from either aluminum at a minimum 0.019 inch (0.48 mm) thickness or corrosion-resistant steel at a minimum 0.0149 inch (0.38 mm) thickness shall not be required to be tested with a ripped or cut longitudinal gap.

    1. Noncombustible material. Material that complies with the requirements for noncombustible materials in Section 202.
    2. Fire-retardant-treated wood. Fire-retardant-treated wood identified for exterior use and meeting the requirements of Section 2303.2 of the International Building Code.
    3. Fire-retardant-treated wood roof coverings. Roof assemblies containing fire-retardant-treated wood shingles and shakes that comply with the requirements of Section 1505.6 of the International Building Code and classified as Class A roof assemblies as required in Section 1505.2 of the International Building Code.

    504.7 Appendages and Projections. Unenclosed accessory structures attached to buildings with habitable spaces and projections, such as decks, shall be not less than 1-hour fire-resistance-rated construction, heavy timber construction or constructed of one of the following:

    1. Approved noncombustible materials.
    2. Fire-retardant-treated wood identified for exterior use and meeting the requirements of Section 2303.2 of the International Building Code.
    3. Ignition-resistant building materials in accordance with Section 503.2.

    2021 Exception: Coated materials shall not be used as the walking surface of decks.

    504.7.1 Underfloor Areas. Where the attached structure is located and constructed so that the structure or any portion thereof projects over a descending slope surface greater than 10 percent, the area below the structure shall have underfloor areas enclosed to within 6 inches (152 mm) of the ground, with exterior wall construction in accordance with Section 504.5.

    504.11.1 Underfloor Areas. Where the detached structure is located and constructed so that the structure or any portion thereof projects over a descending slope surface greater than 10 percent, the area below the structure shall have underfloor areas enclosed to within 6 inches (152 mm) of the ground, with exterior wall construction in accordance with Section 504.5 or underfloor protection in accordance with Section 504.6.

    Exception: The enclosure shall not be required where the underside of exposed floors and exposed structural columns, beams and supporting walls are protected as required for exterior 1-hour fire-resistance-rated construction or heavy timber construction or fire-retardant-treated wood on the exterior side. The fire-retardant-treated wood shall be labeled for exterior use and meet the requirements of Section 2303.2 of the International Building Code.

    603.2 Fuel Modification. Buildings or structures, constructed in compliance with the conforming defensible space category of Table 503.1, shall comply with the fuel modification distances contained in Table 603.2. For all other purposes the fuel modification distance shall be not less than 30 feet (9144 mm) or to the lot line, whichever is less. Distances specified in Table 603.2 shall be measured on a horizontal plane from the perimeter or projection of the building or structure as shown in Figure 603.2. Distances specified in Table 603.2 are allowed to be increased by the code official because of a site-specific analysis based on local conditions and the fire protection plan.

    603.2.1 Responsible Party. Persons owning, leasing, controlling, operating or maintaining buildings or structures requiring defensible spaces are responsible for modifying or removing nonfire-resistive vegetation on the property owned, leased or controlled by said person.

    603.2.2 Trees. Trees are allowed within the defensible space, provided that the horizontal distance between crowns of adjacent trees and crowns of trees and structures, overhead electrical facilities or unmodified fuel is not less than 10 feet (3048 mm).

    603.2.3 Ground Cover. Deadwood and litter shall be regularly removed from trees. Where ornamental vegetative fuels or cultivated ground cover, such as green grass, ivy, succulents or similar plants are used as ground cover, they are allowed to be within the designated defensible space, provided that they do not form a means of transmitting fire from the native growth to any structure.

    607.1 General. Firewood and combustible material shall not be stored in unenclosed spaces beneath buildings or structures, or on decks or under eaves, canopies or other projections or overhangs. Where required by the code official, storage of firewood and combustible material stored in the defensible space shall be located not less than 20 feet (6096 mm) from structures and separated from the crown of trees by a horizontal distance of not less than 15 feet (4572 mm).

    607.2 Storage for Off-Site Use. Firewood and combustible materials not for consumption on the premises shall be stored so as to not pose a hazard. See Appendix A.

     

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

    5.4 Overhanging Projections. Decks, and other projections from the home like balconies, carports, patio covers, etc. should be constructed of heavy timber, noncombustible materials like metal or concrete, or exterior-rated fire-retardant-treated wood or ignition resistant materials.

     

    ASTM E84 - 20 Standard Test Method for Surface Burning Characteristics of Building Materials

    Significance and Use

    4.1 This test method is intended to provide only comparative measurements of surface flame spread and smoke density measurements with that of select grade red oak and fiber-cement board surfaces under the specific fire exposure conditions described herein.

    4.2 This test method exposes a nominal 24-ft (7.32-m) long by 20-in. (508-mm) wide specimen to a controlled air flow and flaming fire exposure adjusted to spread the flame along the entire length of the select grade red oak specimen in 51/2 min.

    4.3 This test method does not provide for the following:

    4.3.1 Measurement of heat transmission through the tested surface.

    4.3.2 The effect of aggravated flame spread behavior of an assembly resulting from the proximity of combustible walls and ceilings.

    4.3.3 Classifying or defining a material as noncombustible, by means of a flame spread index by itself.

    1. Scope

    1.1 This fire-test-response standard for the comparative surface burning behavior of building materials is applicable to exposed surfaces such as walls and ceilings. The test is conducted with the specimen in the ceiling position with the surface to be evaluated exposed face down to the ignition source. The material, product, or assembly shall be capable of being mounted in the test position during the test. Thus, the specimen shall either be self-supporting by its own structural quality, held in place by added supports along the test surface, or secured from the back side.

    1.2 Test Method E84 is a 10-min fire-test response method. The following standards address testing of materials in accordance with test methods that are applications or variations of the test method or apparatus used for Test Method E84:

    1.2.1 Materials required by the user to meet an extended 30-min duration tunnel test shall be tested in accordance with Test Method E2768.

    1.2.2 Wires and cables for use in air-handling spaces shall be tested in accordance with NFPA 262.

    1.2.3 Pneumatic tubing for control systems shall be tested in accordance with UL 1820.

    1.2.4 Combustible sprinkler piping shall be tested in accordance with UL 1887.

    1.2.5 Optical fiber and communications raceways for use in air handling spaces shall be tested in accordance with UL 2024.

    1.3 The purpose of this test method is to determine the relative burning behavior of the material by observing the flame spread along the specimen. Flame spread and smoke developed index are reported. However, there is not necessarily a relationship between these two measurements.

    1.4 The use of supporting materials on the underside of the test specimen has the ability to lower the flame spread index from those which might be obtained if the specimen could be tested without such support. These test results do not necessarily relate to indices obtained by testing materials without such support.

    1.5 Testing of materials that melt, drip, or delaminate to such a degree that the continuity of the flame front is destroyed, results in low flame spread indices that do not relate directly to indices obtained by testing materials that remain in place.

    ASTM D70312

    1. Scope

    1.1 This specification covers procedures to establish a performance rating for wood-plastic composite and plastic lumber for use as exterior deck boards, stair treads, guards, and handrails. The purpose of this specification is to establish a basis for code recognition of these products or systems in exterior applications. The products addressed in this specification are considered combustible.

    NOTE 1: While wood-plastic composites contain wood or other cellulosic materials, the presence of wood or other cellulosic materials in plastic lumber is not required by this specification. Due to non-wood materials in wood-plastic composites and plastic lumber the structural, physical, fire, and other attributes may not be similar to those of wood.

    1.1.1 The plastic component of wood-plastic composites and plastic lumber covered by this specification shall consist primarily of thermoplastics.

    1.2 Deck boards, stair treads, guards, and handrails covered by this specification are permitted to be of any code compliant shape and thickness (solid or non-solid).

    1.3 Wood-plastic composites and plastic lumber are produced in a broad range of fiber and/or resin formulations. It is recognized that the performance requirements in this specification are valid for any material or combination of materials used as deck boards, stair treads, guards, or handrails.

     

    State of California Building Materials Listing Program

    For construction in the state of California, the Office of the State Fire Marshal has set up a program, called the Building Materials Listing Program (BML), which tests and approves different building materials in regards to their fire resilience. Search for fire-resistant decking products on the site’s Building Materials Listings – Search Listing Services feature.

    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

    The new home guidance applies equally to retrofit homes.

    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)
    International Code Council
    Organization(s)
    ICC
    Publication Date
    Description
    2021 edition of the code establishing regulations to safeguard life and property from the intrusion of wildland fire and to prevent structure fires from spreading to wildland fuels; regulates defensible space and provides ignition-resistant construction requirements to protect against fire exposure...
    Author(s)
    Connor McGuigan
    Organization(s)
    Sierra Club
    Publication Date
    Description
    Article from the Sierra Club explaining 5 steps to take to ensure your home's resistance to wildfires, including site maintenance and roof construction guidelines.
    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)
    Bolton
    Organization(s)
    Journal of Light Construction
    Publication Date
    Description
    Article describing codes and test methods related to fire-resistant construction of decks.
    Author(s)
    Milne
    Organization(s)
    UCLA
    Publication Date
    Description
    Wildfire resistant home checklist from Murray Milne, a professor of architecture at UCLA, who outlines seven steps to take to improve a home's chance of survival during a wildfire.
    Author(s)
    University of California Cooperative Extension
    Organization(s)
    University of California Cooperative Extension
    Publication Date
    Description
    Guidelines from the University of California Cooperative Extension on how fires spread, how homes typically burn, and what homeowners can do to prepare their homes for wildfire season.
    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)
    Bueche,
    Foley
    Organization(s)
    CSFS
    Publication Date
    Description
    Wildfire construction guidelines from the Colorado State Forest Service focusing on site design and building materials to mitigate damage to homes in wildfire-prone areas.
    Author(s)
    FireSafe Montana
    Organization(s)
    FireSafe Montana
    Publication Date
    Description
    Ignition resistant residential construction and landscaping guidelines from FireSafe Montana.
    Author(s)
    CalFire
    Organization(s)
    State of California
    Publication Date
    Description
    Webpage offering recommendations to homeowners and contractors for retrofitting a home to make it more resistant to wildfires.
    Author(s)
    National Wildfire Coordinating Group
    Organization(s)
    National Wildfire Coordinating Group
    Publication Date
    Description
    Online course describing the behavior of wildfires for firefighters.
    Author(s)
    National Fire Protection Association
    Organization(s)
    NFPA
    Publication Date
    Description
    Factsheet describing defensible space and wildfire risk reduction steps that homeowners can take to make their homes safer during a wildfire.
    Author(s)
    Insurance Institute for Business & Home Safety,
    National Fire Protection Association
    Organization(s)
    IBHS,
    NFPA
    Publication Date
    Description
    Fact sheet describing research conducted by the Insurance Institute for Business & Home Safety into how burning embers can ignite softwood decks like redwood and cedar and how to minimize the likelihood these decks will be ignited by embers.
    Author(s)
    Canada Northwest Territories Department of Environment and Natural Resources
    Organization(s)
    Canada Northwest Territories Department of Environment and Natural Resources
    Publication Date
    Description
    Website describing how wildfires spread and how fuels, weather, and topography influence fires.
    *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

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